Document and Entity Information - shares	9 Months Ended
Document and Entity Information - shares	Sep. 30, 2018	Oct. 31, 2018
Document and Entity Information [Abstract]
Entity Registrant Name	MGIC INVESTMENT CORP
Entity Central Index Key	0000876437
Current Fiscal Year End Date	--12-31
Entity Current Reporting Status	Yes
Entity Filer Category	Large Accelerated Filer
Entity Common Stock, Shares Outstanding		361,589,994
Document Fiscal Year Focus	2018
Document Fiscal Period Focus	Q3
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Sep. 30, 2018

CONSOLIDATED BALANCE SHEETS - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Investment portfolio:
Fixed income, available for sale, at fair value (amortized cost, 2018 - $5,042,011; 2017 - $4,946,278)	$ 4,969,612	$ 4,983,315
Equity securities, at fair value (cost, 2018 - $4,134; 2017 - $7,223)	7,720
Equity securities, at fair value (cost, 2018 - $4,134; 2017 - $7,223)		7,246
Other invested assets, at cost	3,100	0
Total investment portfolio	4,980,432	4,990,561
Cash and cash equivalents	266,997	99,851
Accrued investment income	45,366	46,060
Reinsurance recoverable on loss reserves	33,281	48,474
Reinsurance recoverable on paid losses	3,111	3,872
Premiums receivable	51,640	54,045
Home office and equipment, net	50,055	44,936
Deferred insurance policy acquisition costs	18,665	18,841
Deferred income taxes, net	111,613	234,381
Other assets	95,948	78,478
Total assets	5,657,108	5,619,499
Liabilities:
Loss reserves	721,046	985,635
Unearned premiums	407,614	392,934
Federal Home Loan Bank advance	155,000	155,000
Senior notes	419,425	418,560
Convertible junior subordinated debentures	256,872	256,872
Other liabilities	207,620	255,972
Total liabilities	2,167,577	2,464,973
Contingencies
Shareholders’ equity:
Common stock (one dollar par value, shares authorized 1,000,000; shares issued 2018 - 371,353; 2017 - 370,567; shares outstanding 2018 - 362,155; 2017 - 370,567)	371,353	370,567
Paid-in capital	1,857,639	1,850,582
Treasury stock at cost (shares 2018 - 9,198)	(100,059)	0
Accumulated other comprehensive loss, net of tax	(128,931)	(43,783)
Retained earnings	1,489,529	977,160
Total shareholders’ equity	3,489,531	3,154,526
Total liabilities and shareholders’ equity	$ 5,657,108	$ 5,619,499

CONSOLIDATED BALANCE SHEETS (Parenthetical) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Statement of Financial Position [Abstract]
Fixed maturities, amortized cost	$ 5,042,011	$ 4,946,278
Equity securities, cost	$ 4,134
Equity securities, cost		$ 7,223
Common stock, par value (in dollars per share)	$ 1	$ 1
Common stock, shares authorized (in shares)	1,000,000,000	1,000,000,000
Common stock, shares issued (in shares)	371,353,000	370,567,000
Common stock, shares outstanding (in shares)	362,155,000	370,567,000
Treasury stock, shares at cost (in shares)	9,198,000	0

CONSOLIDATED STATEMENTS OF OPERATIONS - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Premiums written:
Direct	$ 280,229	$ 287,918	$ 824,989	$ 828,986
Assumed	(3,020)	(91)	(843)	1,882
Ceded	(25,326)	(31,931)	(79,921)	(92,436)
Net premiums written	251,883	255,896	744,225	738,432
Increase in unearned premiums, net	(1,457)	(18,813)	(14,728)	(41,110)
Net premiums earned	250,426	237,083	729,497	697,322
Investment income, net of expenses	36,380	30,402	103,003	89,595
Net realized investment gains (losses)	1,114	(50)	(1,112)	(227)
Other revenue	2,525	2,925	6,827	7,862
Total revenues	290,445	270,360	838,215	794,552
Losses and expenses:
Losses incurred, net	(1,518)	29,747	8,877	84,705
Amortization of deferred policy acquisition costs	3,156	2,985	8,573	7,799
Other underwriting and operating expenses, net	43,655	39,888	131,587	119,164
Interest expense	13,258	13,273	39,737	43,779
Loss on debt extinguishment	0	0	0	65
Total losses and expenses	58,551	85,893	188,774	255,512
Income before tax	231,894	184,467	649,441	539,040
Provision for income taxes	49,994	64,440	137,090	210,593
Net income	$ 181,900	$ 120,027	$ 512,351	$ 328,447
Earnings per share:
Basic (in dollars per share)	$ 0.50	$ 0.32	$ 1.40	$ 0.91
Diluted (in dollars per share)	$ 0.49	$ 0.32	$ 1.36	$ 0.86
Weighted average common shares outstanding - basic (in shares)	362,180	370,586	367,190	359,613
Weighted average common shares outstanding - diluted (in shares)	382,905	391,087	387,765	395,870

CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Statement of Comprehensive Income [Abstract]
Net income	$ 181,900	$ 120,027	$ 512,351	$ 328,447
Other comprehensive (loss) income, net of tax:
Change in unrealized investment gains and losses	(12,077)	11,544	(86,452)	49,414
Benefit plan adjustments	440	(147)	1,322	(442)
Foreign currency translation adjustment	0	0	0	31
Other comprehensive (loss) income, net of tax	(11,637)	11,397	(85,130)	49,003
Comprehensive income	$ 170,263	$ 131,424	$ 427,221	$ 377,450

CONSOLIDATED STATEMENTS OF SHAREHOLDERS' EQUITY - USD ($) $ in Thousands	Total	Common stock	Paid-in capital	Treasury stock	Accumulated other comprehensive (loss) income	Retained earnings
Balance, beginning of period at Dec. 31, 2016		$ 359,400	$ 1,782,337	$ (150,359)	$ (75,100)	$ 632,717
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net common stock issued under share-based compensation plans		776	(7,558)
Issuance of common stock		10,386	60,903
Equity compensation			10,578
Repurchase of common stock				0
Reissuance of treasury stock, net				150,359		(21,740)
Other comprehensive (loss) income, net of tax	$ 49,003				49,003
Net income	328,447					328,447
Balance, end of period at Sep. 30, 2017	3,130,149	370,562	1,846,260	0	(26,097)	939,424
Balance, beginning of period at Dec. 31, 2017	3,154,526	370,567	1,850,582	0	(43,801)	977,178
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net common stock issued under share-based compensation plans		786	(8,917)
Issuance of common stock		0	0
Equity compensation			15,974
Repurchase of common stock				(100,059)
Reissuance of treasury stock, net				0		0
Other comprehensive (loss) income, net of tax	(85,130)				(85,130)
Net income	512,351					512,351
Balance, end of period at Sep. 30, 2018	$ 3,489,531	$ 371,353	$ 1,857,639	$ (100,059)	$ (128,931)	$ 1,489,529

CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017
Cash flows from operating activities:
Net income	$ 512,351	$ 328,447
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	45,267	48,882
Deferred tax expense	145,397	165,250
Net realized investment losses	1,112	227
Loss on debt extinguishment	0	65
Change in certain assets and liabilities:
Accrued investment income	694	1,145
Reinsurance recoverable on loss reserves	15,193	4,615
Reinsurance recoverable on paid losses	761	326
Premium receivable	2,405	(1,546)
Deferred insurance policy acquisition costs	176	(1,265)
Profit commission receivable	(9,098)	(3,899)
Loss reserves	(264,589)	(333,662)
Unearned premiums	14,680	41,079
Return premium accrual	(18,600)	(18,000)
Current income taxes	(75,393)	34,974
Other, net	13,191	(10,282)
Net cash provided by operating activities	383,547	256,356
Cash flows from investing activities:
Purchases of investments	(1,074,849)	(775,043)
Proceeds from sales of investments	338,939	233,198
Proceeds from maturity of fixed income securities	594,679	547,699
Net increase in payable for securities	43,679	3,738
Additions to property and equipment	(10,659)	(12,121)
Net cash used in investing activities	(108,211)	(2,529)
Cash flows from financing activities:
Proceeds from revolving credit facility	0	150,000
Repayment of revolving credit facility	0	(150,000)
Purchase or repayment of convertible senior notes	0	(145,620)
Payment of original issue discount - convertible senior notes	0	(4,504)
Repurchase of common stock	(100,059)	0
Payment of debt issuance costs	0	(1,630)
Payment of withholding taxes related to share-based compensation net share settlement	(8,131)	(6,782)
Net cash used in financing activities	(108,190)	(158,536)
Net increase in cash and cash equivalents	167,146	95,291
Cash and cash equivalents at beginning of period	99,851	155,410
Cash and cash equivalents at end of period	$ 266,997	$ 250,701

Nature of Business and Basis of Presentation	9 Months Ended
Nature of Business and Basis of Presentation	Sep. 30, 2018
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Nature of Business and Basis of Presentation	Nature of Business and Basis of Presentation MGIC Investment Corporation is a holding company which, through Mortgage Guaranty Insurance Corporation (“MGIC”), is principally engaged in the mortgage insurance business. We provide mortgage insurance to lenders throughout the United States and to government sponsored entities to protect against loss from defaults on low down payment residential mortgage loans. MGIC Assurance Corporation (“MAC”), an insurance subsidiary of MGIC, provides insurance for certain mortgages under Fannie Mae and Freddie Mac (the “GSEs”) credit risk transfer programs and is a participant in the Fannie Mae Enterprise-Paid Mortgage Insurance pilot. The accompanying unaudited consolidated financial statements of MGIC Investment Corporation and its wholly-owned subsidiaries have been prepared in accordance with the instructions to Form 10-Q as prescribed by the Securities and Exchange Commission (“SEC”) for interim reporting and do not include all of the other information and disclosures required by accounting principles generally accepted in the United States of America (“GAAP”). These statements should be read in conjunction with the consolidated financial statements and notes thereto for the year ended December 31, 2017 included in our 2017 Annual Report on Form 10-K. As used below, “we,” “our” and “us” refer to MGIC Investment Corporation’s consolidated operations or to MGIC Investment Corporation, as the context requires. In the opinion of management, the accompanying financial statements include all adjustments, consisting primarily of normal recurring accruals, necessary to fairly state our consolidated financial position and consolidated results of operations for the periods indicated. The consolidated results of operations for the interim period may not be indicative of the results that may be expected for the year ending December 31, 2018. Substantially all of our insurance written since 2008 has been for loans purchased by the GSEs. We operate under the Private Mortgage Insurer Eligibility Requirements ("PMIERs") of the GSEs that became effective December 31, 2015 and which have been amended from time to time. The financial requirements of the PMIERs require a mortgage insurer’s "Available Assets" (generally only the most liquid assets of an insurer) to equal or exceed its "Minimum Required Assets" (which are based on an insurer's book of insurance in force, calculated from tables of factors with several risk dimensions and subject to a floor amount). Based on our interpretation of the PMIERs, as of September 30, 2018, MGIC’s Available Assets are in excess of its Minimum Required Assets; and MGIC is in compliance with the financial requirements of the PMIERs and eligible to insure loans purchased by the GSEs. Reclassifications Certain reclassifications to 2017 amounts have been made in the accompanying financial statements to conform to the 2018 presentation. Subsequent events We have considered subsequent events through the date of this filing. Refer to Note 16 - “Subsequent Events” for information regarding MGIC’s execution of a fully collateralized excess of loss reinsurance agreement.

New Accounting Pronouncements

9 Months Ended

Sep. 30, 2018

New Accounting Pronouncements and Changes in Accounting Principles [Abstract]

New Accounting Pronouncements

Accounting standards effective in 2018, or early adopted, and relevant to our financial statements

Table 2.1 shows the relevant amendments to accounting standards that we implemented for the year beginning January 1, 2018; none had a material impact on our consolidated financial statements or disclosures.



	Table	2.1
Standard / Interpretation
Standard / Interpretation	Amended Standards				Effective date
	ASC 718		Compensation - Stock Compensation
			•	ASU 2017-09 - Scope of Modification Accounting	January 1, 2018
	ASC 310		Receivables - Nonrefundable Fees and Other Costs
			•	ASU 2017-08 - Premium Amortization on Purchased Callable Debt Securities	January 1, 2019
	ASC 715		Compensation - Retirement Benefits
			•	ASU 2017-07 - Improving the Presentation of Net Periodic Pension Cost and Net Periodic Postretirement Benefit Cost	January 1, 2018
	ASC 825		Financial Instruments - Overall
			•	ASU 2016-01 - Recognition and Measurement of Financial Assets and Financial Liabilities	January 1, 2018

Stock Compensation - Scope of Modification Accounting

In May 2017, the FASB issued updated guidance related to a change in the terms or conditions (modification) of a share-based award. The updated guidance provides that an entity should account for the effects of a modification unless the fair value and vesting conditions of the modified award and the classification of the award (equity or liability instrument) are the same as the original award immediately before the modification. The updated guidance is effective for annual periods beginning after December 15, 2017, including interim periods within those annual periods.


◦	Adoption impact: The adoption of this guidance had no impact on our consolidated financial statements or disclosures.

Premium Amortization on Purchased Callable Debt Securities

In March 2017, the FASB issued updated guidance to amend the amortization period for certain purchased callable debt securities held at a premium, shortening the amortization period to the earliest call date. This updated guidance aligns with how callable debt securities, in the United States, are generally quoted, priced, and traded, which incorporates consideration of calls (also referred to as “yield-to-worst” pricing). The updated guidance is effective for annual periods beginning after December 15, 2018, including interim periods within those annual periods, but allows for early adoption.


◦	Adoption impact: We adopted this guidance as of January 1, 2018 with no impact to our consolidated financial statements or disclosures as our accounting policy adhered to the updated guidance.

Improving the Presentation of Net Periodic Pension Cost and Net Periodic Postretirement Benefit Cost

In March 2017, the FASB issued updated guidance intended to improve the reporting of net benefit cost in the financial statements. The updated guidance requires that an employer report the service cost component of pension and post-retirement benefit costs in the same financial statement caption as other compensation costs arising from services rendered by employees during the period. The other components of net benefit cost are required to be presented in the statement of operations separately from the service cost component and outside a subtotal of income from operations, if one is presented. Previous guidance did not prescribe where the amount of net benefit cost should be presented in an employer’s statement of operations and did not require entities to disclose by line item the amount of net benefit cost that is included in the statement of operations. The updated guidance is effective for annual periods beginning after December 15, 2017, including interim periods within those annual periods.

◦

Adoption impact: The adoption of this guidance had no impact on our consolidated financial statements or disclosures as the service cost component is reported in the same financial statement caption as other compensation costs and we do not present a subtotal of income outside of income from operations. The service cost component of our benefit plans is disclosed in Note 10 - “Benefit Plans” to our consolidated financial statements.

Recognition and Measurement of Financial Assets and Financial Liabilities

In January 2016, the FASB issued updated guidance to address the recognition, measurement, presentation, and disclosure of certain financial instruments. The updated guidance requires equity investments, except those accounted for under the equity method of accounting, that have a readily determinable fair value to be measured at fair value with changes in fair value recognized in net income. Equity investments that do not have readily determinable fair values may be remeasured at fair value either upon the occurrence of an observable price change or upon identification of an impairment. A qualitative assessment for impairment is required for equity investments without readily determinable fair values. The updated guidance also eliminates the requirement to disclose the method and significant assumptions used to estimate the fair value of financial instruments measured at amortized cost on the balance sheet. Further, the updated guidance clarifies that entities should evaluate the need for a valuation allowance on a deferred tax asset related to available-for-sale securities in combination with the entities’ other deferred tax assets. The updated guidance is effective for annual periods beginning after December 15, 2017, including interim periods within those annual periods and requires recognition of a cumulative effect adjustment at adoption.

◦

Adoption impact: The adoption of this guidance resulted in an immaterial cumulative effect adjustment to our 2018 beginning accumulated other comprehensive (loss) income and retained earnings to recognize unrealized gains on equity investments. At December 31, 2017, equity investments were classified as available-for-sale on the consolidated balance sheet. Upon adoption, the updated guidance eliminated the available-for-sale balance sheet classification for equity securities.

In February 2018, the FASB issued a separate update for technical corrections and improvements to clarify certain aspects of the guidance described above. This update clarifies the presentation of investments in, among other things, Federal Home Loan Bank stock and prohibits those investments from being shown with equity securities.


◦	Adoption impact: At March 31, 2018, and periods subsequent, the value of our investment in Federal Home Loan Bank of Chicago (“FHLB”) stock, which is carried at cost, is presented within “Other invested assets” on our consolidated balance sheet.

Prospective Accounting Standards

Table 2.2 shows the relevant new amendments to accounting standards, which are not yet effective or adopted.



	Table	2.2
Standard / Interpretation					Effective date
Standard / Interpretation	Amended Standards
	ASC 326		Financial Instruments - Credit Losses
			•	ASU 2016-13 - Measurement of Credit Losses on Financial Instruments	January 1, 2020
	ASC 820		Fair Value Measurement
			•	ASU 2018-13 - Changes to the Disclosure Requirements for Fair Value Measurements	January 1, 2020
	ASC 715		Compensation - Retirement Benefits
			•	ASU 2018-14 - Changes to the Disclosure Requirements for Defined Benefit Plans	January 1, 2021

Measurement of Credit Losses on Financial Instruments

In June 2016, the FASB issued updated guidance that requires immediate recognition of estimated credit losses expected to occur over the remaining life of many financial instruments. Entities will be required to utilize a current expected credit losses (“CECL”) methodology that incorporates their forecast of future economic conditions into their loss estimate unless such forecast is not reasonable and supportable, in which case the entity will revert to historical loss experience. Any allowance for CECL reduces the amortized cost basis of the financial instrument to the amount an entity expects to collect. Credit losses relating to available-for-sale fixed maturity securities are to be recorded through an allowance for credit losses, rather than a write-down of the asset, with the amount of the allowance limited to the amount by which fair value is less than amortized cost. In addition, the length of time a security has been in an unrealized loss position will no longer impact the determination of whether a credit loss exists. The updated guidance is not prescriptive about certain aspects of estimating expected credit losses, including the specific methodology to use, and therefore will require significant judgment in application. The updated guidance is effective for annual periods beginning after December 15, 2019, including interim periods within those annual periods. Early adoption is permitted for annual and interim periods in fiscal years beginning after December 15, 2018. We are currently evaluating the impacts the adoption of this guidance will have on our consolidated financial statements, but do not expect it to have a material impact on our consolidated financial statements or disclosures.

Changes to the Disclosure Requirements for Fair Value Measurement

In August 2018, the FASB issued updated guidance that changes the disclosure requirements for fair value measurements. The updated guidance removed the requirement to disclose the amount of and reasons for transfers between Level 1 and Level 2 of the fair value hierarchy; the policy for timing of transfers between levels; and the valuation processes for Level 3 fair value measurements. The updated guidance clarifies that the measurement uncertainty disclosure is to communicate information about the uncertainty in measurements as of the reporting date. Further, the updated guidance will require disclosure of changes in unrealized gains and losses for the period included in other comprehensive income for recurring Level 3 fair value measurements held at the end of the reporting period; and the range and weighted average of significant unobservable inputs used to develop Level 3 fair value measurements. The updated guidance is effective for annual periods beginning after December 15, 2019, including interim periods within those annual periods. Early adoption was permitted upon issuance of this update. An entity is permitted to early adopt any guidance that removed or modified disclosures upon issuance of this update and to delay adoption of the additional disclosures until its effective date. We are currently evaluating the impacts the adoption of this guidance will have on our consolidated financial statement disclosures, but do not expect it to have a material impact.

Changes to the Disclosure Requirements for Defined Benefit Plans

In August 2018, the FASB issued amendments to modify the disclosure requirements for defined benefit plans. The updated guidance removed the requirements to identify amounts that are expected to be reclassified out of accumulated other comprehensive income and recognized as components of net periodic benefit cost in the coming year and the effects of a one-percentage-point change in assumed health care cost trend rates on service and interest cost and on the postretirement benefit obligation. The updated guidance added disclosures for the weighted-average interest crediting rates for cash balance plans and other plans with interest crediting rates and explanations for significant gains and losses related to changes in the benefit obligation for the period. The updated guidance is effective for annual periods beginning after December 15, 2020. Early adoption is permitted. An entity should apply the amendments on a retrospective basis to all periods presented. We are currently evaluating the impacts the adoption of this guidance will have on our consolidated financial statement disclosures, but do not expect it to have a material impact.

Debt

9 Months Ended

Sep. 30, 2018

Debt Disclosure [Abstract]

Debt

Debt obligations

The par value of our long-term debt obligations and their aggregate carrying values as of September 30, 2018 and December 31, 2017 are presented in table 3.1 below.



	Table	3.1
Long-term debt obligations	(In millions)		September 30, 2018			December 31, 2017
	FHLB Advance		$	155.0		$	155.0
	5.75% Senior Notes		425.0			425.0
	9% Convertible Junior Subordinated Debentures ⁽¹⁾		256.9			256.9
	Long-term debt, par value		836.9			836.9
	Debt issuance costs		(5.6		)	(6.5		)
	Long-term debt, carrying value		$	831.3		$	830.4

⁽¹⁾

Convertible at any time prior to maturity at the holder’s option, at an initial conversion rate, which is subject to adjustment, of 74.0741 shares per $1,000 principal amount, representing an initial conversion price of approximately $13.50 per share. If a holder elects to convert its debentures, deferred interest owed on the debentures being converted is also converted into shares of our common stock. The conversion rate for any deferred interest is based on the average price that our shares traded at during a 5-day period immediately prior to the election to convert. In lieu of issuing shares of common stock upon conversion of the debentures, we may, at our option, make a cash payment to converting holders for all or some of the shares of our common stock otherwise issuable upon conversion.

The 5.75% Senior Notes, 9% Convertible Junior Subordinated Debentures, and any amounts drawn on our revolving credit facility, are obligations of our holding company, MGIC Investment Corporation, and not of its subsidiaries. In addition to interest on amounts drawn, the unused portion of our revolving credit facility is subject to recurring commitment fees, which are reflected in interest payments. The Federal Home Loan Bank Advance (the “FHLB Advance”) is an obligation of MGIC.

Table 3.2 below presents interest payments on our debt obligations.



	Table	3.2
Interest payments on debt obligations			Nine Months Ended September 30,
	(In millions)		2018		2017
	Revolving credit facility		$	0.5	$	0.5
	FHLB Advance		2.3		2.2
	5% Convertible Senior Notes		—		3.6
	2% Convertible Senior Notes		—		2.1
	5.75% Senior Notes		24.4		25.1
	9% Convertible Junior Subordinated Debentures		11.6		11.6
	Total interest payments		$	38.8	$	45.1

Reinsurance

9 Months Ended

Sep. 30, 2018

Reinsurance Disclosures [Abstract]

Reinsurance

The reinsurance agreements to which we are a party, excluding captive agreements (which were immaterial), are discussed below. The effect of all of our reinsurance agreements on premiums earned and losses incurred is shown in table 4.1 below.



	Table	4.1
Effect of Reinsurance			Three Months Ended September 30,						Nine Months Ended September 30,
	(In thousands)		2018			2017			2018			2017
	Premiums earned:
	Direct		$	275,044		$	268,709		$	808,531		$	789,317
	Assumed		709			312			936			472
	Ceded		(25,327		)	(31,938		)	(79,970		)	(92,467		)
	Net premiums earned		$	250,426		$	237,083		$	729,497		$	697,322

	Losses incurred:
	Direct		$	(2,081	)	$	35,313		$	12,642		$	99,122
	Assumed		55			(97		)	45			69
	Ceded		508			(5,469		)	(3,810		)	(14,486		)
	Losses incurred, net		$	(1,518	)	$	29,747		$	8,877		$	84,705

Quota share reinsurance

We utilize quota share reinsurance to manage our exposure to losses resulting from our mortgage guaranty insurance policies and to provide reinsurance capital credit under the PMIERs. Each of the reinsurers under our QSR Transactions has an insurer financial strength rating of A- or better by Standard and Poor’s Rating Services, A.M. Best or both.

2018 QSR Transaction. We entered into a QSR transaction with a group of unaffiliated reinsurers with an effective date of January 1, 2018 (“2018 QSR Transaction”), which provides coverage on eligible new business written in 2018. Under the 2018 QSR Transaction, we will cede losses incurred and premiums on or after the effective date through December 31, 2029, at which time the agreement expires. Early termination of the agreement can be elected by us effective December 31, 2021, and annually thereafter, for a fee, or under specified scenarios for no fee upon prior written notice, including if we will receive less than 90% of the full credit amount under the PMIERs for the risk ceded in any required calculation period.

The structure of the 2018 QSR Transaction is a 30% quota share for all policies covered, with a 20% ceding commission as well as a profit commission. Generally, under the 2018 QSR Transaction, we will receive a profit commission provided that the loss ratio on the loans covered under the agreement remains below 62%.

2017 and 2015 QSR Transactions.

Our 2017 quota share reinsurance agreement (“2017 QSR Transaction”) provides coverage on eligible new business written January 1, 2017 through December 29, 2017. Under the 2017 QSR Transaction we cede losses incurred and premiums on or after the effective date through December 31, 2028, at which time the agreement expires. Early termination of the agreement can be elected by us effective December 31, 2021 for a fee, or under specified scenarios for no fee upon prior written notice, including if we will receive less than 90% of the full credit amount under the PMIERs for the risk ceded in any required calculation period.

Our 2015 quota share reinsurance agreement (“2015 QSR Transaction”) provides coverage on eligible business written before 2017. Under the 2015 QSR Transaction cedes losses incurred and premiums through December 31, 2024, at which time the agreement expires. Early termination of the agreement can be elected by us effective December 31, 2018 for a fee, or bi-annually thereafter, or under specified scenarios for no fee upon prior written notice, including if we will receive less than 90% of the full credit amount under the PMIERs for the risk ceded in any required calculation period.

The structure of both the 2017 QSR Transaction and 2015 QSR Transaction is a 30% quota share for all policies covered, with a 20% ceding commission as well as a profit commission. Generally, under the 2017 and 2015 QSR Transactions, we will receive a profit commission provided that the loss ratio on the loans covered under the agreement remains below 60%.

Table 4.2 below presents a summary of our quota share reinsurance agreements, excluding captive agreements (which were immaterial), for the three and nine months ended September 30, 2018 and 2017.



	Table	4.2
Quota share reinsurance			Three Months Ended September 30,					Nine Months Ended September 30,
Quota share reinsurance	(In thousands)		2018			2017		2018		2017
	Ceded premiums written and earned, net of profit commission ⁽¹⁾		$	25,248		$	30,880	$	79,716	$	88,692
	Ceded losses incurred		(522		)	5,879		3,531		14,990
	Ceding commissions ⁽²⁾		12,983			12,500		38,268		36,751
	Profit commission		39,664			31,621		111,622		95,063


⁽¹⁾	Under our QSR Transactions, premiums are ceded on an earned and received basis as defined in the agreements.


⁽²⁾	Ceding commissions are reported within Other underwriting and operating expenses, net on the consolidated statements of operations.

Under the terms of the QSR Transactions, ceded premiums, ceding commission and profit commission are settled net on a quarterly basis. The ceded premiums due after deducting the related ceding commission and profit commission is reported within “Other liabilities” on the consolidated balance sheets.

The reinsurance recoverable on loss reserves related to our QSR Transactions was $33.1 million as of September 30, 2018 and $39.3 million as of December 31, 2017. The reinsurance recoverable balance is secured by funds on deposit from the reinsurers which are based on the funding requirements of PMIERs that address ceded risk.

Excess of Loss reinsurance

Refer to Note 16 - “Subsequent Events,” for further information about our excess of loss reinsurance agreement entered into in October 2018. The excess of loss reinsurance agreement covers losses beginning August 1, 2018, but had no material impact on our consolidated financial statements as of and for the three and nine months ended September 30, 2018.

Litigation and Contingencies	9 Months Ended
Litigation and Contingencies	Sep. 30, 2018
Commitments and Contingencies Disclosure [Abstract]
Litigation and Contingencies	Litigation and Contingencies Before paying an insurance claim, we review the loan and servicing files to determine the appropriateness of the claim amount. When reviewing the files, we may determine that we have the right to rescind coverage on the loan. We refer to insurance rescissions and denials of claims collectively as “rescissions” and variations of that term. In addition, our insurance policies generally provide that we can reduce or deny a claim if the servicer did not comply with its obligations under our insurance policy. We call such reduction of claims “curtailments.” In recent quarters, an immaterial percentage of claims received in a quarter have been resolved by rescissions. In each of 2017 and the first nine months of 2018, curtailments reduced our average claim paid by approximately 5.6% and 6.3%, respectively. Our loss reserving methodology incorporates our estimates of future rescissions, curtailments, and reversals of rescissions and curtailments. A variance between ultimate actual rescission, curtailment and reversal rates and our estimates, as a result of the outcome of litigation, settlements or other factors, could materially affect our losses. When the insured disputes our right to rescind coverage or curtail claims, we generally engage in discussions in an attempt to settle the dispute. If we are unable to reach a settlement, the outcome of a dispute ultimately may be determined by legal proceedings. Under ASC 450-20, until a liability associated with settlement discussions or legal proceedings becomes probable and can be reasonably estimated, we consider our claim payment or rescission resolved for financial reporting purposes and do not accrue an estimated loss. Where we have determined that a loss is probable and can be reasonably estimated, we have recorded our best estimate of our probable loss. In addition to matters for which we have recorded a probable loss, we are involved in other discussions and/or proceedings with insureds with respect to our claims paying practices. Although it is reasonably possible that when these matters are resolved we will not prevail in all cases, we are unable to make a reasonable estimate or range of estimates of the potential liability. We estimate the maximum exposure associated with matters where a loss is reasonably possible to be approximately $286 million. This estimate of maximum exposure is based upon currently available information and is subject to significant judgment, numerous assumptions and known and unknown uncertainties. The matters underlying the estimate of maximum exposure will change from time to time. This estimate of our maximum exposure does not include interest or consequential or exemplary damages. Mortgage insurers, including MGIC, have been involved in litigation and regulatory actions related to alleged violations of the anti-referral fee provisions of the Real Estate Settlement Procedures Act, which is commonly known as RESPA, and the notice provisions of the Fair Credit Reporting Act, which is commonly known as FCRA. While these proceedings in the aggregate have not resulted in material liability for MGIC, there can be no assurance that the outcome of future proceedings, if any, under these laws would not have a material adverse affect on us. In addition, various regulators, including the CFPB, state insurance commissioners and state attorneys general may bring other actions seeking various forms of relief in connection with alleged violations of RESPA. The insurance law provisions of many states prohibit paying for the referral of insurance business and provide various mechanisms to enforce this prohibition. While we believe our practices are in conformity with applicable laws and regulations, it is not possible to predict the eventual scope, duration or outcome of any such reviews or investigations nor is it possible to predict their effect on us or the mortgage insurance industry. Through a non-insurance subsidiary, we utilize our underwriting skills to provide an outsourced underwriting service to our customers known as contract underwriting. As part of the contract underwriting activities, that subsidiary is responsible for the quality of the underwriting decisions in accordance with the terms of the contract underwriting agreements with customers. That subsidiary may be required to provide certain remedies to its customers if certain standards relating to the quality of our underwriting work are not met, and we have an established reserve for such future obligations. Claims for remedies may be made a number of years after the underwriting work was performed. The underwriting remedy expense for 2017 and the first nine months of 2018 was immaterial to our consolidated financial statements. In addition to the matters described above, we are involved in other legal proceedings in the ordinary course of business. In our opinion, based on the facts known at this time, the ultimate resolution of these ordinary course legal proceedings will not have a material adverse effect on our financial position or consolidated results of operations. See Note 11 – “Income Taxes” for a description of federal income tax contingencies.

Earnings per Share

9 Months Ended

Sep. 30, 2018

Earnings Per Share [Abstract]

Earnings per Share

Basic earnings per share (“EPS”) is calculated by dividing net income by the weighted average number of shares of common stock outstanding. For purposes of calculating basic EPS, vested restricted stock and restricted stock units (“RSUs”) are considered outstanding. Diluted EPS includes the components of basic EPS and also gives effect to dilutive common stock equivalents. We calculate diluted EPS using the treasury stock method and if-converted method. Under the treasury stock method, diluted EPS reflects the potential dilution that could occur if unvested RSUs result in the issuance of common stock. Under the if-converted method, diluted EPS reflects the potential dilution that could occur if our convertible debt instruments result in the issuance of common stock. The determination of potentially issuable shares does not consider the satisfaction of the conversion requirements and the shares are included in the determination of diluted EPS as of the beginning of the period, if dilutive. During the three and nine months ended September 30, 2018, we had 9% Debentures outstanding that could result in potentially issuable shares.

Table 6.1 reconciles the numerators and denominators used to calculate basic and diluted EPS.



	Table	6.1
Earnings per share			Three Months Ended September 30,				Nine Months Ended September 30,
Earnings per share	(In thousands, except per share data)		2018		2017		2018		2017
	Basic earnings per share:
	Net income		$	181,900	$	120,027	$	512,351	$	328,447
	Weighted average common shares outstanding - basic		362,180		370,586		367,190		359,613
	Basic earnings per share		$	0.50	$	0.32	$	1.40	$	0.91

	Diluted earnings per share:
	Net income		$	181,900	$	120,027	$	512,351	$	328,447
	Interest expense, net of tax ⁽¹⁾:
	2% Convertible Senior Notes		—		—		—		907
	5% Convertible Senior Notes		—		—		—		1,709
	9% Convertible Junior Subordinated Debentures		4,566		3,757		13,698		11,270
	Diluted income available to common shareholders		$	186,466	$	123,784	$	526,049	$	342,333

	Weighted average common shares outstanding - basic		362,180		370,586		367,190		359,613
	Effect of dilutive securities:
	Unvested RSUs		1,697		1,473		1,547		1,367
	2% Convertible Senior Notes		—		—		—		11,119
	5% Convertible Senior Notes		—		—		—		4,743
	9% Convertible Junior Subordinated Debentures		19,028		19,028		19,028		19,028
	Weighted average common shares outstanding - diluted		382,905		391,087		387,765		395,870
	Diluted earnings per share		$	0.49	$	0.32	$	1.36	$	0.86


⁽¹⁾	The periods ended September 30, 2018 and 2017 were tax-effected at a rate of 21% and 35%, respectively.

Investments

9 Months Ended

Sep. 30, 2018

Investments [Abstract]

Investments

Fixed income securities

The amortized cost, gross unrealized gains and losses, and fair value of investments in fixed income securities classified as available-for-sale at September 30, 2018 and December 31, 2017 are shown in tables 7.1a and 7.1b below.



	Table	7.1a
Details of fixed income securities by category - current year			September 30, 2018
	(In thousands)		Amortized Cost		Gross Unrealized Gains		Gross Unrealized (Losses) ⁽¹⁾			Fair Value
	U.S. Treasury securities and obligations of U.S. government corporations and agencies		$	179,395	$	174	$	(3,353	)	$	176,216
	Obligations of U.S. states and political subdivisions		1,738,417		17,797		(21,608		)	1,734,606
	Corporate debt securities		2,296,218		1,152		(42,305		)	2,255,065
	Asset backed securities (“ABS”)		71,481		—		(546		)	70,935
	Residential mortgage backed securities (“RMBS”)		166,522		35		(11,594		)	154,963
	Commercial mortgage backed securities (“CMBS”)		281,980		214		(11,974		)	270,220
	Collateralized loan obligations (“CLO”)		307,998		67		(458		)	307,607
	Total fixed income securities		5,042,011		19,439		(91,838		)	4,969,612



	Table	7.1b
Details of fixed income securities by category - prior year-end			December 31, 2017
	(In thousands)		Amortized Cost		Gross Unrealized Gains		Gross Unrealized (Losses) ⁽¹⁾			Fair Value
	U.S. Treasury securities and obligations of U.S. government corporations and agencies		$	179,850	$	274	$	(1,278	)	$	178,846
	Obligations of U.S. states and political subdivisions		2,105,063		56,210		(8,749		)	2,152,524
	Corporate debt securities		2,065,475		10,532		(9,169		)	2,066,838
	ABS		4,925		—		(2		)	4,923
	RMBS		189,153		60		(7,364		)	181,849
	CMBS		301,014		1,204		(4,906		)	297,312
	CLOs		100,798		304		(79		)	101,023
	Total fixed income securities		4,946,278		68,584		(31,547		)	4,983,315


⁽¹⁾	At September 30, 2018 and December 31, 2017, there were no other-than-temporary impairment losses recorded in other comprehensive income.

We had $13.4 million and $13.6 million of investments at fair value on deposit with various states as of September 30, 2018 and December 31, 2017, respectively, due to regulatory requirements of those state insurance departments.

The amortized cost and fair values of fixed income securities at September 30, 2018, by contractual maturity, are shown in table 7.2 below. Expected maturities will differ from contractual maturities because borrowers may have the right to call or prepay obligations with or without call or prepayment penalties. Because most ABS, RMBS, CMBS, and CLOs provide for periodic payments throughout their lives, they are listed in separate categories.



	Table	7.2
Fixed income securities maturity schedule			September 30, 2018
	(In thousands)		Amortized Cost		Fair Value
	Due in one year or less		$	511,087	$	509,952
	Due after one year through five years		1,552,123		1,526,802
	Due after five years through ten years		940,185		918,757
	Due after ten years		1,210,635		1,210,376
			$	4,214,030	$	4,165,887

	ABS		71,481		70,935
	RMBS		166,522		154,963
	CMBS		281,980		270,220
	CLOs		307,998		307,607
	Total as of September 30, 2018		$	5,042,011	$	4,969,612

Proceeds from sales of fixed income securities classified as available-for-sale were $338.9 million and $233.2 million during the nine months ended September 30, 2018 and 2017, respectively. Gross gains of $0.4 million and $0.9 million and gross losses of $3.3 million and $1.1 million were realized on those sales during the nine months ended September 30, 2018 and 2017, respectively.

During the three and nine months ended September 30, 2018, we recorded other-than-temporary impairment (“OTTI”) losses of $0.5 million and $1.8 million, respectively, due to our intent to sell certain investments. During each of the three and nine months ended September 30, 2017, there were no OTTI losses recognized.

Equity securities

The cost and fair value of investments in equity securities at September 30, 2018 and December 31, 2017 are shown in tables 7.3a and 7.3b below. As described in Note 2 - “New Accounting Pronouncements,” under updated guidance regarding the “Recognition and Measurement of Financial Assets and Financial Liabilities” which became effective on January 1, 2018, the amount of our FHLB stock investment has been reclassified and presented in “Other invested assets” on our consolidated balance sheet as of September 30, 2018.



	Table	7.3a
Details of equity security investments - current year			September 30, 2018
	(In thousands)		Cost		Gross Gains		Gross Losses			Fair Value
	Equity securities		$	4,134	$	3,667	$	(81	)	$	7,720



	Table	7.3b
Details of equity security investments - prior year-end			December 31, 2017
	(In thousands)		Cost		Gross Gains		Gross Losses			Fair Value
	Equity securities		$	7,223	$	39	$	(16	)	$	7,246

For the nine months ended September 30, 2018, we recognized $3.6 million of net gains on equity securities still held as of September 30, 2018. The net gains reflect the fair value increase in certain equity securities of a privately held entity that were re-valued in the third quarter by independent parties and subsequently sold in a transaction completed in October 2018. The net gains are reported in Net realized investment gains (losses) on our consolidated statement of operations for the three and nine months ended September 30, 2018.

Other invested assets

Other invested assets include an investment in FHLB stock that is carried at cost, which due to its nature approximates fair value. Ownership of FHLB stock provides access to a secured lending facility, and our current FHLB Advance amount is secured by eligible collateral whose fair value is maintained at a minimum of 102% of the outstanding principal balance. As of September 30, 2018, that collateral consisted of fixed income securities included in our total investment portfolio, and cash and cash equivalents, with a total fair value of $166.1 million.

Unrealized investment losses

Tables 7.4a and 7.4b below summarize, for all available-for-sale investments in an unrealized loss position at September 30, 2018 and December 31, 2017, the aggregate fair value and gross unrealized loss by the length of time those securities have been continuously in an unrealized loss position. The fair value amounts reported in tables 7.4a and 7.4b are estimated using the process described in Note 8 - “Fair Value Measurements” to these consolidated financial statements and in Note 3 - “Significant Accounting Policies” of the notes to the consolidated financial statements in our 2017 Annual Report on Form 10-K.



	Table	7.4a
Investments unrealized losses - current year			September 30, 2018
			Less Than 12 Months					12 Months or Greater					Total
	(In thousands)		Fair Value		Unrealized Losses			Fair Value		Unrealized Losses			Fair Value		Unrealized Losses
	U.S. Treasury securities and obligations of U.S. government corporations and agencies		$	89,759	$	(583	)	$	78,769	$	(2,770	)	$	168,528	$	(3,353	)
	Obligations of U.S. states and political subdivisions		643,147		(12,356		)	245,763		(9,252		)	888,910		(21,608		)
	Corporate debt securities		1,782,640		(29,184		)	299,549		(13,121		)	2,082,189		(42,305		)
	ABS		70,935		(546		)	—		—			70,935		(546		)
	RMBS		4,930		(183		)	149,648		(11,411		)	154,578		(11,594		)
	CMBS		81,972		(1,763		)	160,039		(10,211		)	242,011		(11,974		)
	CLOs		201,700		(458		)	—		—			201,700		(458		)
	Total		$	2,875,083	$	(45,073	)	$	933,768	$	(46,765	)	$	3,808,851	$	(91,838	)



	Table	7.4b
Investments unrealized losses - prior year-end			December 31, 2017
			Less Than 12 Months					12 Months or Greater					Total
	(In thousands)		Fair Value		Unrealized Losses			Fair Value		Unrealized Losses			Fair Value		Unrealized Losses
	U.S. Treasury securities and obligations of U.S. government corporations and agencies		$	144,042	$	(796	)	$	31,196	$	(482	)	$	175,238	$	(1,278	)
	Obligations of U.S. states and political subdivisions		505,311		(3,624		)	211,684		(5,125		)	716,995		(8,749		)
	Corporate debt securities		932,350		(4,288		)	200,716		(4,881		)	1,133,066		(9,169		)
	ABS		4,923		(2		)	—		—			4,923		(2		)
	RMBS		14,979		(280		)	166,329		(7,084		)	181,308		(7,364		)
	CMBS		51,096		(358		)	138,769		(4,548		)	189,865		(4,906		)
	CLOs		14,243		(7		)	3,568		(72		)	17,811		(79		)
	Equity securities		226		(2		)	431		(14		)	657		(16		)
	Total		$	1,667,170	$	(9,357	)	$	752,693	$	(22,206	)	$	2,419,863	$	(31,563	)

The unrealized losses in all categories of our investments at September 30, 2018 and December 31, 2017 were primarily caused by changes in interest rates between the time of purchase and the respective fair value measurement date. There were 810 and 586 securities in an unrealized loss position at September 30, 2018 and December 31, 2017, respectively.

Fair Value Measurements

9 Months Ended

Sep. 30, 2018

Fair Value Disclosures [Abstract]

Fair Value Measurements

Recurring fair value measurements

In accordance with fair value accounting guidance, we applied the following fair value hierarchy to measure fair value for assets and liabilities:

Level 1 - Quoted prices for identical instruments in active markets that we can access. Financial assets utilizing Level 1 inputs primarily include U.S. Treasury securities and equity securities.

Level 2 - Quoted prices for similar instruments in active markets that we can access; quoted prices for identical or similar instruments in markets that are not active; and inputs, other than quoted prices, that are observable in the marketplace for the instrument. The observable inputs are used in valuation models to calculate the fair value based on the type of instrument. Financial assets utilizing Level 2 inputs primarily include obligations of U.S. government corporations and agencies, corporate bonds, mortgage-backed securities, asset-backed securities, and most municipal bonds.

Level 3 - Valuations derived from valuation techniques in which one or more significant inputs or value drivers are unobservable. The inputs used to derive the fair value of Level 3 securities reflect our own assumptions about the assumptions a market participant would use in pricing an asset or liability, or for certain of our equity securities, independent fair market valuations provided to us. Our non-financial assets that are classified as Level 3 securities consist of real estate acquired through claim settlement. The fair value of real estate acquired is the lower of our acquisition cost or a percentage of the appraised value. The percentage applied to the appraised value is based upon our historical sales experience adjusted for current trends.

Assets measured at fair value, by hierarchy level, as of September 30, 2018 and December 31, 2017 are shown in tables 8.1a and 8.1b below. The fair value of the assets is estimated using the process described above, and more fully in Note 3 - “Significant Accounting Policies” of the notes to the consolidated financial statements in our 2017 Annual Report on Form 10-K.



	Table	8.1a
Fair value hierarchy - current year			September 30, 2018
Fair value hierarchy - current year	(In thousands)		Total Fair Value		Quoted Prices in Active Markets for Identical Assets (Level 1)		Significant Other Observable Inputs (Level 2)		Significant Unobservable Inputs (Level 3)
	U.S. Treasury securities and obligations of U.S. government corporations and agencies		$	176,216	$	29,584	$	146,632	$	—
	Obligations of U.S. states and political subdivisions		1,734,606		—		1,734,529		77
	Corporate debt securities		2,255,065		—		2,255,065		—
	ABS		70,935		—		70,935		—
	RMBS		154,963		—		154,963		—
	CMBS		270,220		—		270,220		—
	CLOs		307,607		—		307,607		—
	Total fixed income securities		4,969,612		29,584		4,939,951		77
	Equity securities		7,720		2,889		—		4,831
	Total investments at fair value		$	4,977,332	$	32,473	$	4,939,951	$	4,908
	Real estate acquired ⁽¹⁾		$	12,339	$	—	$	—	$	12,339



	Table	8.1b
Fair value hierarchy - prior year-end			December 31, 2017
Fair value hierarchy - prior year-end	(In thousands)		Total Fair Value		Quoted Prices in Active Markets for Identical Assets (Level 1)		Significant Other Observable Inputs (Level 2)		Significant Unobservable Inputs (Level 3)
	U.S. Treasury securities and obligations of U.S. government corporations and agencies		$	178,846	$	81,598	$	97,248	$	—
	Obligations of U.S. states and political subdivisions		2,152,524		—		2,152,253		271
	Corporate debt securities		2,066,838		—		2,066,838		—
	ABS		4,923		—		4,923		—
	RMBS		181,849		—		181,849		—
	CMBS		297,312		—		297,312		—
	CLOs		101,023		—		101,023		—
	Total fixed income securities		4,983,315		81,598		4,901,446		271
	Equity securities ⁽²⁾		7,246		2,978		—		4,268
	Total investments at fair value		$	4,990,561	$	84,576	$	4,901,446	$	4,539
	Real estate acquired ⁽¹⁾		$	12,713	$	—	$	—	$	12,713


⁽¹⁾	Real estate acquired through claim settlement, which is held for sale, is reported in Other assets on the consolidated balance sheets.


⁽²⁾	Equity securities in Level 3 are carried at cost, which approximates fair value. See “Reconciliations of Level 3 assets” below for information regarding a change in presentation of amounts previously included in Level 3 Equity securities.

Reconciliations of Level 3 assets

For assets measured at fair value using significant unobservable inputs (Level 3), a reconciliation of the beginning and ending balances for the three and nine months ended September 30, 2018 and 2017 is shown in tables 8.2a and 8.2b and 8.3a and 8.3b below. As described in Note 2 - “New Accounting Pronouncements,” under updated guidance regarding the Recognition and Measurement of Financial Assets and Financial Liabilities which became effective on January 1, 2018, our investment in FHLB stock is no longer presented with equity securities. Prior to the updated guidance, our FHLB stock was included in our Level 3 equity securities. As shown in table 8.3a below, for the nine months ended September 30, 2018, we have transferred our FHLB stock out of Level 3 assets, and it is carried at cost, which approximates fair value, on our consolidated balance sheet in “Other invested assets” as of September 30, 2018. There were no losses included in earnings for those periods attributable to the change in unrealized losses on assets still held at the end of the applicable period.



	Table	8.2a
Development of assets and liabilities classified within level 3 - current year quarter			Three Months Ended September 30, 2018
	(In thousands)		Debt Securities			Equity Securities		Total Investments			Real Estate Acquired
	Balance at June 30, 2018		$	192		$	1,168	$	1,360		$	13,321
	Total realized gains (losses):
	Included in earnings and reported as net realized investment gains		—			3,663		3,663			—
	Included in earnings and reported as losses incurred, net		—			—		—			(450		)
	Purchases		—			—		—			7,979
	Sales		(115		)	—		(115		)	(8,511		)
	Balance at September 30, 2018		$	77		$	4,831	$	4,908		$	12,339



	Table	8.2b
Development of assets and liabilities classified within level 3 - prior year quarter			Three Months Ended September 30, 2017
	(In thousands)		Debt Securities			Equity Securities		Total Investments			Real Estate Acquired
	Balance at June 30, 2017		$	577		$	4,268	$	4,845		$	10,271
	Total realized gains (losses):
	Included in earnings and reported as losses incurred, net		—			—		—			(592		)
	Purchases		—			—		—			8,881
	Sales		(197		)	—		(197		)	(6,832		)
	Balance at September 30, 2017		$	380		$	4,268	$	4,648		$	11,728



	Table	8.3a
Development of assets and liabilities classified within level 3 - current year to date			Nine Months Ended September 30, 2018
	(In thousands)		Debt Securities			Equity Securities			Total Investments			Real Estate Acquired
	Balance at December 31, 2017		$	271		$	4,268		$	4,539		$	12,713
	Transfers out of Level 3		—			(3,100		)	(3,100		)	—
	Total realized gains (losses):
	Included in earnings and reported as net realized investment gains		—			3,663			3,663			—
	Included in earnings and reported as losses incurred, net		—			—			—			(1,104		)
	Purchases		—			—			—			24,742
	Sales		(194		)	—			(194		)	(24,012		)
	Balance at September 30, 2018		$	77		$	4,831		$	4,908		$	12,339



	Table	8.3b
Development of assets and liabilities classified within level 3 - prior year to date			Nine Months Ended September 30, 2017
	(In thousands)		Debt Securities			Equity Securities		Total Investments			Real Estate Acquired
	Balance at December 31, 2016		$	691		$	4,268	$	4,959		$	11,748
	Total realized gains (losses):
	Included in earnings and reported as losses incurred, net		—			—		—			(818		)
	Purchases		—			—		—			26,985
	Sales		(311		)	—		(311		)	(26,187		)
	Balance at September 30, 2017		$	380		$	4,268	$	4,648		$	11,728

Certain financial instruments, including insurance contracts, are excluded from these fair value disclosure requirements. The carrying values of cash and cash equivalents (Level 1) and accrued investment income (Level 2) approximated their fair values. Additional fair value disclosures related to our investment portfolio are included in Note 7 – “Investments.”

Financial liabilities not measured at fair value

We incur financial liabilities in the normal course of our business. Table 8.4 presents the carrying value and fair value of our financial liabilities disclosed, but not carried, at fair value at September 30, 2018 and December 31, 2017. The fair values of our 5.75% Senior Notes and 9% Convertible Junior Subordinated Debentures were based on observable market prices. The fair value of the FHLB Advance was estimated using cash flows discounted at current incremental borrowing rates for similar borrowing arrangements. In all cases the fair values of the financial liabilities below are categorized as Level 2.



	Table	8.4
Fair value measurements - liabilities			September 30, 2018				December 31, 2017
	(In thousands)		Carrying Value		Fair Value		Carrying Value		Fair Value
	FHLB Advance		$	155,000	$	148,288	$	155,000	$	152,124
	5.75% Senior Notes		419,425		445,430		418,560		465,473
	9% Convertible Junior Subordinated Debentures		256,872		347,458		256,872		353,507
	Total financial liabilities		$	831,297	$	941,176	$	830,432	$	971,104

- Definition

The entire disclosure for the fair value of financial instruments (as defined), including financial assets and financial liabilities (collectively, as defined), and the measurements of those instruments as well as disclosures related to the fair value of non-financial assets and liabilities. Such disclosures about the financial instruments, assets, and liabilities would include: (1) the fair value of the required items together with their carrying amounts (as appropriate); (2) for items for which it is not practicable to estimate fair value, disclosure would include: (a) information pertinent to estimating fair value (including, carrying amount, effective interest rate, and maturity, and (b) the reasons why it is not practicable to estimate fair value; (3) significant concentrations of credit risk including: (a) information about the activity, region, or economic characteristics identifying a concentration, (b) the maximum amount of loss the entity is exposed to based on the gross fair value of the related item, (c) policy for requiring collateral or other security and information as to accessing such collateral or security, and (d) the nature and brief description of such collateral or security; (4) quantitative information about market risks and how such risks are managed; (5) for items measured on both a recurring and nonrecurring basis information regarding the inputs used to develop the fair value measurement; and (6) for items presented in the financial statement for which fair value measurement is elected: (a) information necessary to understand the reasons for the election, (b) discussion of the effect of fair value changes on earnings, (c) a description of [similar groups] items for which the election is made and the relation thereof to the balance sheet, the aggregate carrying value of items included in the balance sheet that are not eligible for the election; (7) all other required (as defined) and desired information.

+ References + Details

Other Comprehensive Income

9 Months Ended

Sep. 30, 2018

Comprehensive Income (Loss), Net of Tax, Attributable to Parent [Abstract]

Other Comprehensive Income

The pretax and related income tax (expense) benefit components of our other comprehensive income (loss) for the three and nine months ended September 30, 2018 and 2017 are included in table 9.1 below.



	Table	9.1
Components of other comprehensive (loss) income			Three Months Ended September 30,						Nine Months Ended September 30,
	(In thousands)		2018			2017			2018			2017
	Net unrealized investment (losses) gains arising during the period		$	(15,288	)	$	17,761		$	(109,433	)	$	76,022
	Income tax benefit (expense)		3,211			(6,217		)	22,981			(26,608		)
	Net of taxes		(12,077		)	11,544			(86,452		)	49,414

	Net changes in benefit plan assets and obligations		558			(226		)	1,674			(680		)
	Income tax (expense) benefit		(118		)	79			(352		)	238
	Net of taxes		440			(147		)	1,322			(442		)

	Net changes in unrealized foreign currency translation adjustment		—			—			—			45
	Income tax (expense)		—			—			—			(14		)
	Net of taxes		—			—			—			31

	Total other comprehensive (loss) income		(14,730		)	17,535			(107,759		)	75,387
	Total income tax benefit (expense)		3,093			(6,138		)	22,629			(26,384		)
	Total other comprehensive (loss) income, net of tax		$	(11,637	)	$	11,397		$	(85,130	)	$	49,003

The pretax and related income tax benefit (expense) components of the amounts reclassified from our accumulated other comprehensive loss (“AOCL”) to our consolidated statements of operations for the three and nine months ended September 30, 2018 and 2017 are included in table 9.2 below.



	Table	9.2
Reclassifications from AOCL			Three Months Ended September 30,						Nine Months Ended September 30,
	(In thousands)		2018			2017			2018			2017
	Reclassification adjustment for net realized (losses) ⁽¹⁾		$	(2,567	)	$	(427	)	$	(6,279	)	$	(2,566	)
	Income tax benefit		539			150			1,318			898
	Net of taxes		(2,028		)	(277		)	(4,961		)	(1,668		)

	Reclassification adjustment related to benefit plan assets and obligations ⁽²⁾		(558		)	226			(1,674		)	680
	Income tax benefit (expense)		118			(79		)	352			(238		)
	Net of taxes		(440		)	147			(1,322		)	442

	Total reclassifications		(3,125		)	(201		)	(7,953		)	(1,886		)
	Total income tax benefit		657			71			1,670			660
	Total reclassifications, net of tax		$	(2,468	)	$	(130	)	$	(6,283	)	$	(1,226	)


⁽¹⁾	Increases (decreases) Net realized investment (losses) gains on the consolidated statements of operations.


⁽²⁾	Decreases (increases) Other underwriting and operating expenses, net on the consolidated statements of operations.

A rollforward of AOCL for the nine months ended September 30, 2018, including amounts reclassified from AOCL, are included in table 9.3 below.



	Table	9.3
Rollforward of AOCL			Nine Months Ended September 30, 2018
Rollforward of AOCL	(In thousands)		Net unrealized gains and losses on available-for-sale securities			Net benefit plan assets and obligations recognized in shareholders' equity			Total AOCL
	Balance, December 31, 2017, net of tax		$	29,257		$	(73,058	)	$	(43,801	)
	Other comprehensive income before reclassifications		(91,413		)	—			(91,413		)
	Less: Amounts reclassified from AOCL		(4,961		)	(1,322		)	(6,283		)
	Balance, September 30, 2018, net of tax		$	(57,195	)	$	(71,736	)	$	(128,931	)

Benefit Plans

9 Months Ended

Sep. 30, 2018

Retirement Benefits [Abstract]

Benefit Plans

Tables 10.1 and 10.2 provide the components of net periodic benefit cost for our pension, supplemental executive retirement and other postretirement benefit plans for the three and nine months ended September 30, 2018 and 2017.



	Table	10.1
Components of net periodic benefit cost			Three Months Ended September 30,
Components of net periodic benefit cost			Pension and Supplemental Executive Retirement Plans						Other Postretirement Benefit Plans
	(In thousands)		2018			2017			2018			2017
	Service cost		$	2,633		$	2,389		$	290		$	203
	Interest cost		3,774			3,869			208			176
	Expected return on plan assets		(5,563		)	(5,025		)	(1,590		)	(1,312		)
	Amortization of net actuarial losses/(gains)		1,734			1,543			(62		)	—
	Amortization of prior service cost/(credit)		(88		)	(107		)	(1,026		)	(1,662		)
	Net periodic benefit cost (benefit)		$	2,490		$	2,669		$	(2,180	)	$	(2,595	)



	Table	10.2
Components of net periodic benefit cost			Nine Months Ended September 30,
Components of net periodic benefit cost			Pension and Supplemental Executive Retirement Plans						Other Postretirement Benefit Plans
	(In thousands)		2018			2017			2018			2017
	Service cost		$	7,898		$	7,167		$	870		$	610
	Interest cost		11,321			11,606			625			529
	Expected return on plan assets		(16,688		)	(15,074		)	(4,769		)	(3,936		)
	Amortization of net actuarial losses/(gains)		5,203			4,627			(187		)	—
	Amortization of prior service cost/(credit)		(263		)	(320		)	(3,078		)	(4,987		)
	Net periodic benefit cost (benefit)		$	7,471		$	8,006		$	(6,539	)	$	(7,784	)

We currently intend to make contributions totaling $11 million to our qualified pension plan and supplemental executive retirement plan in 2018.

Income Taxes	9 Months Ended
Income Taxes	Sep. 30, 2018
Income Tax Disclosure [Abstract]
Income Taxes	Income Taxes We have approximately $153.5 million of net operating loss (“NOL”) carryforwards as of September 30, 2018. Any unutilized carryforwards are scheduled to expire at the end of tax years 2032 through 2033. We evaluate the realizability of our deferred tax assets including our NOL carryforwards on a quarterly basis. Based on our analysis, we have concluded that all of our deferred tax assets are fully realizable and therefore no valuation allowance existed at September 30, 2018 and December 31, 2017. Tax Contingencies As previously disclosed, the Internal Revenue Service (“IRS”) completed examinations of our federal income tax returns for the years 2000 through 2007 and issued proposed assessments for taxes, interest and penalties related to our treatment of the flow-through income and loss from an investment in a portfolio of residual interests of Real Estate Mortgage Investment Conduits. In July 2018, we finalized an agreement with the IRS to settle all issues in the examination and related U.S. Tax Court case; the settlement has been approved by the U.S. Tax Court. The expected impact of the agreed upon settlement was previously reflected in our consolidated statements of operations. With the approval of our settlement by the U.S. Tax Court, our unrecognized tax benefits have been reduced by $144.9 million in the third quarter of 2018. As of September 30, 2018, we have no unrecognized tax benefits.

Loss Reserves

9 Months Ended

Sep. 30, 2018

Insurance Loss Reserves [Abstract]

Loss Reserves

We establish reserves to recognize the estimated liability for losses and loss adjustment expenses (“LAE”) related to defaults on insured mortgage loans. Loss reserves are established by estimating the number of loans in our inventory of delinquent loans that will result in a claim payment, which is referred to as the claim rate, and further estimating the amount of the claim payment, which is referred to as claim severity.

Estimation of losses is inherently judgmental. The conditions that affect the claim rate and claim severity include the current and future state of the domestic economy, including unemployment and the current and future strength of local housing markets; exposure on insured loans; the amount of time between default and claim filing; and curtailments and rescissions. The actual amount of the claim payments may be substantially different than our loss reserve estimates. Our estimates could be adversely affected by several factors, including a deterioration of regional or national economic conditions, including unemployment, leading to a reduction in borrowers’ income and thus their ability to make mortgage payments, and a drop in housing values which may affect borrower willingness to continue to make mortgage payments when the value of the home is below the mortgage balance. Changes to our estimates could result in a material impact to our consolidated results of operations and financial position, even in a stable economic environment.

The “Losses incurred” section of table 12.1 below shows losses incurred on delinquencies that occurred in the current year and in prior years. The amount of losses incurred relating to delinquencies that occurred in the current year represents the estimated amount to be ultimately paid on such delinquencies. The amount of losses incurred relating to delinquencies that occurred in prior years represents the difference between the actual claim rate and severity associated with those delinquencies resolved in the current year compared to the estimated claim rate and severity at the prior year-end, as well as a re-estimation of amounts to be ultimately paid on delinquencies continuing from the end of the prior year. This re-estimation of the claim rate and severity is the result of our review of current trends in the delinquent inventory, such as percentages of delinquencies that have resulted in a claim, the amount of the claims relative to the average loan exposure, changes in the relative level of delinquencies by geography and changes in average loan exposure.

Losses incurred on delinquencies that occurred in the current year decreased in the first nine months of 2018 compared to the same period in 2017, primarily due to a decrease in the number of new delinquencies, net of related cures and a decrease in the estimated claim rate on delinquencies that occurred in the current year.

For the nine months ended September 30, 2018 and 2017, we experienced favorable loss reserve development on previously received delinquencies. This was, in large part, due to the resolution of approximately 65% and 59%, respectively, of the prior year delinquent inventory, with lower claim rates due to improved cure rates. The favorable loss reserve development resulting from a reduction in the estimated claim rate was partially offset in the nine months ended September 30, 2018 by an increase in our severity assumption on previously received delinquencies.

The “Losses paid” section of table 12.1 below shows the amount of losses paid on delinquencies that occurred in the current year and losses paid on delinquencies that occurred in prior years. For several years, the average time it took to receive a claim associated with a delinquency had increased significantly from our historical experience of approximately twelve months. This was, in part, due to new loss mitigation protocols established by servicers and to changes in some state foreclosure laws that may include, for example, a requirement for additional review and/or mediation processes. In recent quarters, we have experienced a decline in the average time servicers are utilizing to process foreclosures, which has reduced the average time to receive a claim associated with new delinquent notices that do not cure. All else being equal, the longer the period between delinquency and claim filing, the greater the severity.

During the first nine months of 2018 and 2017, our losses paid included amounts paid upon commutation of coverage of pools of non-performing loans (“NPLs”) and/or amounts paid in connection with disputes concerning our claims paying practices. The impacts of these payments were as follows:


•	2018 - 1,243 items were removed from the delinquent inventory with an amount paid of $40 million.


•	2017 - 1,337 items were removed from the delinquent inventory with amount paid of $54 million.

Our estimate of premiums to be refunded on expected claim payments is accrued for separately in “Other Liabilities” on our consolidated balance sheets and approximated $44 million and $61 million at September 30, 2018 and December 31, 2017, respectively.

Table 12.1 provides a reconciliation of beginning and ending loss reserves as of and for the nine months ended September 30, 2018 and 2017.



	Table	12.1
Development of reserves for losses and loss adjustment expenses			Nine months ended September 30,
	(In thousands)		2018			2017
	Reserve at beginning of period		$	985,635		$	1,438,813
	Less reinsurance recoverable		48,474			50,493
	Net reserve at beginning of period		937,161			1,388,320

	Losses incurred:
	Losses and LAE incurred in respect of delinquency notices received in:
	Current year		155,808			219,485
	Prior years ⁽¹⁾		(146,931		)	(134,780		)
	Total losses incurred		8,877			84,705

	Losses paid:
	Losses and LAE paid in respect of delinquency notices received in:
	Current year		2,449			5,474
	Prior years		257,808			407,977
	Reinsurance terminations		(1,984		)	301
	Total losses paid		258,273			413,752
	Net reserve at end of period		687,765			1,059,273
	Plus reinsurance recoverables		33,281			45,878
	Reserve at end of period		$	721,046		$	1,105,151


⁽¹⁾	A negative number for prior year losses incurred indicates a redundancy of prior year loss reserves. See the following table for more information about prior year loss development.

The prior year development of the reserves in the first nine months of 2018 and 2017 is reflected in table 12.2 below.



	Table	12.2
Reserve development on previously received delinquencies			Nine months ended September 30,
	(in millions)		2018			2017
	Decrease in estimated claim rate on primary defaults		$	(184	)	$	(138	)
	Increase in estimated severity on primary defaults		22			(2		)
	Change in estimates related to pool reserves, LAE reserves and reinsurance		15			5
	Total prior year loss development ⁽¹⁾		$	(147	)	$	(135	)


⁽¹⁾	A negative number for prior year loss development indicates a redundancy of prior year loss reserves.

Delinquent inventory

A rollforward of our primary delinquent inventory for the three and nine months ended September 30, 2018 and 2017 appears in table 12.3 below. The information concerning new notices and cures is compiled from monthly reports received from loan servicers. The level of new notice and cure activity reported in a particular month can be influenced by, among other things, the date on which a servicer generates its report, the accuracy of the data provided by servicers, the number of business days in a month, transfers of servicing between loan servicers and whether all servicers have provided the reports in a given month.



	Table	12.3
Delinquent inventory rollforward			Three Months Ended September 30,				Nine Months Ended September 30,
			2018		2017		2018		2017
	Delinquent inventory at beginning of period		36,037		41,317		46,556		50,282
	New notices		13,569		15,950		40,351		45,352
	Cures		(14,197	)	(13,546	)	(47,620	)	(45,382	)
	Paids (including those charged to a deductible or captive)		(1,374	)	(2,195	)	(4,446	)	(7,403	)
	Rescissions and denials		(56	)	(82	)	(200	)	(277	)
	Other items removed from inventory		(581	)	(209	)	(1,243	)	(1,337	)
	Delinquent inventory at end of period		33,398		41,235		33,398		41,235

The decrease in the primary delinquent inventory experienced during 2018 and 2017 was generally across all markets and primarily in book years 2008 and prior. Historically as a default ages it becomes more likely to result in a claim.

Hurricane activity

New delinquent notice activity increased in the fourth quarter of 2017 because of hurricane activity that primarily impacted Puerto Rico, Texas, and Florida in the third quarter of 2017. As a result, the number of loans delinquent three months or less was a higher percentage of our total inventory as of December 31, 2017 than it had been as of September 30, 2017.

Table 12.4 below shows the number of consecutive months a borrower is delinquent.



	Table	12.4
Delinquent inventory - consecutive months in default			September 30, 2018			December 31, 2017			September 30, 2017
	3 months or less		9,484	28	%	17,119	37	%	11,331	27	%
	4-11 months		9,564	29	%	12,050	26	%	11,092	27	%
	12 months or more ^{(1) (2)}		14,350	43	%	17,387	37	%	18,812	46	%
	Total primary delinquent inventory		33,398	100	%	46,556	100	%	41,235	100	%

	Primary claims received inventory included in ending delinquent inventory:		766	2	%	954	2	%	1,063	3	%


⁽¹⁾	Approximately 39%, 45%, and 45% of the primary delinquent inventory delinquent for 12 consecutive months or more has been delinquent for at least 36 consecutive months as of September 30, 2018, December 31, 2017, and September 30, 2017, respectively.


⁽²⁾	The majority of items removed from our delinquent inventory due to commutations of NPLs during the nine months ended September 30, 2018 were delinquent for 12 consecutive months or more as of December 31, 2017.

The number of months a loan is in the delinquent inventory can differ from the number of payments that the borrower has not made or is considered delinquent. These differences typically result from a borrower making monthly payments that do not result in the loan becoming fully current. Table 12.5 below shows the number of payments that a borrower is delinquent.



	Table	12.5
Delinquent inventory - number of payments delinquent			September 30, 2018			December 31, 2017			September 30, 2017
	3 payments or less		14,813	44	%	21,678	46	%	16,916	41	%
	4-11 payments		9,156	28	%	12,446	27	%	10,583	26	%
	12 payments or more ^{(1) (2)}		9,429	28	%	12,432	27	%	13,736	33	%
	Total primary delinquent inventory		33,398	100	%	46,556	100	%	41,235	100	%


⁽¹⁾	Approximately 39%, 43%, and 43% of the primary delinquent inventory with 12 payments or more delinquent has at least 36 payments delinquent as of September 30, 2018, December 31, 2017, and September 30, 2017, respectively.


⁽²⁾	The majority of items removed from our delinquent inventory due to commutations of NPLs during the nine months ended September 30, 2018 had 12 or more payments delinquent as of December 31, 2017.

Pool insurance delinquent inventory decreased to 1,032 at September 30, 2018 from 1,309 at December 31, 2017, and 1,426 at September 30, 2017.

Claims paying practices

Our loss reserving methodology incorporates our estimates of future rescissions and curtailments. A variance between ultimate actual rescission and curtailment rates and our estimates, as a result of the outcome of litigation, settlements or other factors, could materially affect our losses. Our estimate of premiums to be refunded on expected future rescissions is accrued for separately and is included in “Other liabilities” on our consolidated balance sheets. For information about discussions and legal proceedings with customers with respect to our claims paying practices see Note 5 – “Litigation and Contingencies.”

Shareholders' Equity	9 Months Ended
Shareholders' Equity	Sep. 30, 2018
Stockholders' Equity Note [Abstract]
Shareholders' Equity	Shareholders’ Equity Share repurchase program On April 26, 2018, our Board of Directors authorized a share repurchase program under which we may repurchase up to $200 million of our common stock through the end of 2019. Repurchases may be made from time to time on the open market or through privately negotiated transactions. The repurchase program may be suspended for periods or discontinued at any time. During the second quarter of 2018, we repurchased approximately 9.2 million shares of our common stock at a weighted average price per share of $10.88, which included commissions. Change in accounting principle As described in Note 2 - “New Accounting Pronouncements,” during the first quarter of 2018 the updated guidance of “Recognition and Measurement of Financial Assets and Financial Liabilities” became effective. The application of this guidance resulted in an immaterial cumulative effect adjustment to our 2018 beginning accumulated other comprehensive (loss) income and retained earnings to recognize unrealized gains on equity securities. Shareholders Rights Agreement Our Amended and Restated Rights Agreement dated August 1, 2018 (“the 2018 Agreement”) seeks to diminish the risk that our ability to use our NOLs to reduce potential future federal income tax obligations may become substantially limited and to deter certain abusive takeover practices. The benefit of the NOLs would be substantially limited, and the timing of the usage of the NOLs could be substantially delayed, if we were to experience an “ownership change” as defined by Section 382 of the Internal Revenue Code. Under the 2018 Agreement, each outstanding share of our Common Stock is accompanied by one Right. The “Distribution Date” occurs on the earlier of ten days after a public announcement that a person has become an “Acquiring Person,” or ten business days after a person announces or begins a tender offer in which consummation of such offer would result in a person becoming an “Acquiring Person.” An “Acquiring Person” is any person that becomes, by itself or together with its affiliates and associates, a beneficial owner of 5% or more of the shares of our Common Stock then outstanding, but excludes, among others, certain exempt and grandfathered persons as defined in the Agreement. The Rights are not exercisable until the Distribution Date. Each Right will initially entitle shareholders to buy one-tenth of one share of our Common Stock at a Purchase Price of $45 per full share (equivalent to $4.50 for each one-tenth share), subject to adjustment. Each exercisable Right (subject to certain limitations) will entitle its holder to purchase, at the Rights’ then-current Purchase Price, a number of our shares of Common Stock (or if after the Shares Acquisition Date, we are acquired in a business combination, common shares of the acquiror) having a market value at the time equal to twice the Purchase Price. The Rights will expire on March 1, 2020, or earlier as described in the 2018 Agreement. The Rights are redeemable at a price of $0.001 per Right at any time prior to the time a person becomes an Acquiring Person. Other than certain amendments, the Board of Directors may amend the Rights in any respect without the consent of the holders of the Rights.

Share-Based Compensation

9 Months Ended

Sep. 30, 2018

Disclosure of Compensation Related Costs, Share-based Payments [Abstract]

Share-Based Compensation

We have certain share-based compensation plans. Under the fair value method, compensation cost is measured at the grant date based on the fair value of the award and is recognized over the service period which generally corresponds to the vesting period. Awards under our plans generally vest over periods ranging from one to three years.

Table 14.1 shows the number of shares granted to employees and the weighted average fair value per share during the periods presented (shares in thousands).



	Table	14.1
Restricted stock grants			Nine months ended September 30,
Restricted stock grants			2018			2017
			Shares Granted	Weighted Average Share Fair Value		Shares Granted	Weighted Average Share Fair Value
	RSUs subject to performance conditions		1,239	$	15.80	1,237	$	10.41
	RSUs subject only to service conditions		447	15.39		395	10.41

Statutory Information	9 Months Ended
Statutory Information	Sep. 30, 2018
Statutory Capital [Abstract]
Statutory Information	Statutory Information Statutory Capital Requirements The insurance laws of 16 jurisdictions, including Wisconsin, our domiciliary state, require a mortgage insurer to maintain a minimum amount of statutory capital relative to the risk in force (or a similar measure) in order for the mortgage insurer to continue to write new business. We refer to these requirements as the “State Capital Requirements.” While they vary among jurisdictions, the most common State Capital Requirements allow for a maximum risk-to-capital ratio of 25 to 1. A risk-to-capital ratio will increase if (i) the percentage decrease in capital exceeds the percentage decrease in insured risk, or (ii) the percentage increase in capital is less than the percentage increase in insured risk. Wisconsin does not regulate capital by using a risk-to-capital measure but instead requires a minimum policyholder position (“MPP”). The “policyholder position” of a mortgage insurer is its net worth or surplus, contingency reserve and a portion of the reserves for unearned premiums. At September 30, 2018, MGIC’s risk-to-capital ratio was 9.0 to 1, below the maximum allowed by the jurisdictions with State Capital Requirements, and its policyholder position was $2.5 billion above the required MPP of $1.3 billion. In calculating our risk-to-capital ratio and MPP, we are allowed full credit for the risk ceded under our reinsurance transactions with a group of unaffiliated reinsurers. It is possible that under the revised State Capital Requirements discussed below, MGIC will not be allowed full credit for the risk ceded to the reinsurers. If MGIC is not allowed an agreed level of credit under either the State Capital Requirements or the financial requirements of the PMIERs, MGIC may terminate the reinsurance transactions, without penalty. At this time, we expect MGIC to continue to comply with the current State Capital Requirements; however, matters that could negatively affect such compliance are discussed in the rest of these consolidated financial statement footnotes. At September 30, 2018, the risk-to-capital ratio of our combined insurance operations (which includes a reinsurance affiliate) was 9.8 to 1. Reinsurance agreements with an affiliate permit MGIC to write insurance with a higher coverage percentage than it could on its own under certain state-specific requirements. A higher risk-to-capital ratio on a combined basis may indicate that, in order for MGIC to continue to utilize reinsurance agreements with its affiliate, additional capital contributions to the reinsurance affiliate could be needed. The NAIC plans to revise the minimum capital and surplus requirements for mortgage insurers that are provided for in its Mortgage Guaranty Insurance Model Act. In May 2016, a working group of state regulators released an exposure draft of a risk-based capital framework to establish capital requirements for mortgage insurers, although no date has been established by which the NAIC must propose revisions to the capital requirements and certain items have not yet been completely addressed by the framework, including the treatment of ceded risk, minimum capital floors, and action level triggers. Currently, we believe that the PMIERs contain more restrictive capital requirements than the draft Mortgage Guaranty Insurance Model Act in most circumstances. While MGIC currently meets the State Capital Requirements of Wisconsin and all other jurisdictions, it could be prevented from writing new business in the future in all jurisdictions if it fails to meet the State Capital Requirements of Wisconsin, or it could be prevented from writing new business in a particular jurisdiction if it fails to meet the State Capital Requirements of that jurisdiction, and in each case MGIC does not obtain a waiver of such requirements. It is possible that regulatory action by one or more jurisdictions, including those that do not have specific State Capital Requirements, may prevent MGIC from continuing to write new insurance in such jurisdictions. If we are unable to write business in a particular jurisdiction, lenders may be unwilling to procure insurance from us anywhere. In addition, a lender’s assessment of the future ability of our insurance operations to meet the State Capital Requirements or the PMIERs may affect its willingness to procure insurance from us. A possible future failure by MGIC to meet the State Capital Requirements or the PMIERs will not necessarily mean that MGIC lacks sufficient resources to pay claims on its insurance liabilities. While we believe MGIC has sufficient claims paying resources to meet its claim obligations on its insurance in force on a timely basis, matters that could negatively affect MGIC’s claims paying resources are discussed in the rest of these consolidated financial statement footnotes. Dividend restrictions In the third quarter of 2018, MGIC paid a $60 million dividend to our holding company. MGIC is subject to statutory regulations as to payment of dividends. The maximum amount of dividends that MGIC may pay in any twelve-month period without such dividends being subject to regulatory disapproval by the OCI is the lesser of adjusted statutory net income or 10% of statutory policyholders’ surplus as of the preceding calendar year end. Adjusted statutory net income is defined for this purpose to be the greater of statutory net income, net of realized investment gains, for the calendar year preceding the date of the dividend or statutory net income, net of realized investment gains, for the three calendar years preceding the date of the dividend less dividends paid within the first two of the preceding three calendar years. The OCI recognizes only statutory accounting principles prescribed, or practices permitted by the State of Wisconsin for determining and reporting the financial condition and results of operations of an insurance company. The OCI has adopted certain prescribed accounting practices that differ from those found in other states. Specifically, Wisconsin domiciled companies record changes in their contingency reserves through their income statement as a change in underwriting deduction. As a result, in periods in which MGIC is increasing contingency reserves, statutory net income is lowered. For the year ended December 31, 2017, MGIC’s increase in contingency reserves was $473 million and statutory net income was $272 million.

Subsequent Events	9 Months Ended
Subsequent Events	Sep. 30, 2018
Subsequent Events [Abstract]
Subsequent Events	Subsequent Events On October 30, 2018, MGIC entered into a fully collateralized reinsurance agreement with Home Re 2018-1 Ltd. (“Home Re”), an unaffiliated special purpose insurer domiciled in Bermuda, that provides for up to $318.6 million of aggregate excess-of-loss reinsurance coverage as of August 1, 2018 on a portfolio of mortgage insurance policies having an insurance coverage in force date on or after July 1, 2016 and before January 1, 2018. For the reinsurance coverage period, MGIC will retain the first layer of $168.7 million of aggregate losses, and Home Re will then provide second layer coverage up to the outstanding reinsurance coverage amount. The reinsurance coverage premium due to Home Re is calculated by multiplying the outstanding reinsurance coverage amount at the beginning of a period by a coupon rate, which is the sum of one-month LIBOR plus a spread for each class of notes, and then subtracting actual investment income collected on the assets in the reinsurance trust during that period. The aggregate excess of loss reinsurance coverage decreases over a ten-year period, subject to certain conditions, as the underlying covered mortgages amortize, principal is prepaid, or mortgage insurance losses are paid. MGIC has rights to terminate the reinsurance agreement, which includes an option to terminate after seven years from the closing date. Home Re financed the coverage by issuing mortgage insurance-linked notes in an aggregate amount of $318.6 million to unaffiliated investors. The notes have ten-year legal maturities and are non-recourse to any assets of MGIC or its affiliates. The proceeds of the notes were deposited into a reinsurance trust for the benefit of MGIC that will be the source of reinsurance claim payments to MGIC and principal repayments on the mortgage insurance-linked notes. In connection with entering into the reinsurance agreement with Home Re, we concluded that the risk transfer requirements for reinsurance accounting were met as Home Re is assuming significant insurance risk and a reasonable possibility of significant loss. In addition, we assessed whether Home Re was a variable interest entity (“VIE”). A VIE is a legal entity that does not have sufficient equity at risk to finance its activities without additional subordinated financial support or is structured such that equity investors lack the ability to make sufficient decisions relating to the entity’s operations through voting rights or do not substantively participate in gains and losses of the entity. We concluded that Home Re is a VIE. However, given that MGIC (1) does not have the unilateral power to direct the activities that most significantly affect Home Re’s economic performance and (2) does not have the obligation to absorb losses or the right to receive benefits that could be potentially significant to Home Re, consolidation of Home Re is not required.

New Accounting Pronouncements (Policies)

9 Months Ended

Sep. 30, 2018

New Accounting Pronouncements and Changes in Accounting Principles [Abstract]

Prospective Accounting Standards

Accounting standards effective in 2018, or early adopted, and relevant to our financial statements



	Table	2.1
Standard / Interpretation
Standard / Interpretation	Amended Standards				Effective date
	ASC 718		Compensation - Stock Compensation
			•	ASU 2017-09 - Scope of Modification Accounting	January 1, 2018
	ASC 310		Receivables - Nonrefundable Fees and Other Costs
			•	ASU 2017-08 - Premium Amortization on Purchased Callable Debt Securities	January 1, 2019
	ASC 715		Compensation - Retirement Benefits
			•	ASU 2017-07 - Improving the Presentation of Net Periodic Pension Cost and Net Periodic Postretirement Benefit Cost	January 1, 2018
	ASC 825		Financial Instruments - Overall
			•	ASU 2016-01 - Recognition and Measurement of Financial Assets and Financial Liabilities	January 1, 2018

Stock Compensation - Scope of Modification Accounting


◦	Adoption impact: The adoption of this guidance had no impact on our consolidated financial statements or disclosures.

Premium Amortization on Purchased Callable Debt Securities


◦	Adoption impact: We adopted this guidance as of January 1, 2018 with no impact to our consolidated financial statements or disclosures as our accounting policy adhered to the updated guidance.

Improving the Presentation of Net Periodic Pension Cost and Net Periodic Postretirement Benefit Cost

◦

Recognition and Measurement of Financial Assets and Financial Liabilities

◦


◦	Adoption impact: At March 31, 2018, and periods subsequent, the value of our investment in Federal Home Loan Bank of Chicago (“FHLB”) stock, which is carried at cost, is presented within “Other invested assets” on our consolidated balance sheet.

Prospective Accounting Standards

Table 2.2 shows the relevant new amendments to accounting standards, which are not yet effective or adopted.



	Table	2.2
Standard / Interpretation					Effective date
Standard / Interpretation	Amended Standards
	ASC 326		Financial Instruments - Credit Losses
			•	ASU 2016-13 - Measurement of Credit Losses on Financial Instruments	January 1, 2020
	ASC 820		Fair Value Measurement
			•	ASU 2018-13 - Changes to the Disclosure Requirements for Fair Value Measurements	January 1, 2020
	ASC 715		Compensation - Retirement Benefits
			•	ASU 2018-14 - Changes to the Disclosure Requirements for Defined Benefit Plans	January 1, 2021

Measurement of Credit Losses on Financial Instruments

Changes to the Disclosure Requirements for Fair Value Measurement

Changes to the Disclosure Requirements for Defined Benefit Plans

New Accounting Pronouncements New Accounting Pronouncements (Tables)

9 Months Ended

Sep. 30, 2018

New Accounting Pronouncements and Changes in Accounting Principles [Abstract]

Schedule of New Accounting Pronouncements and Changes in Accounting Principles



	Table	2.1
Standard / Interpretation
Standard / Interpretation	Amended Standards				Effective date
	ASC 718		Compensation - Stock Compensation
			•	ASU 2017-09 - Scope of Modification Accounting	January 1, 2018
	ASC 310		Receivables - Nonrefundable Fees and Other Costs
			•	ASU 2017-08 - Premium Amortization on Purchased Callable Debt Securities	January 1, 2019
	ASC 715		Compensation - Retirement Benefits
			•	ASU 2017-07 - Improving the Presentation of Net Periodic Pension Cost and Net Periodic Postretirement Benefit Cost	January 1, 2018
	ASC 825		Financial Instruments - Overall
			•	ASU 2016-01 - Recognition and Measurement of Financial Assets and Financial Liabilities	January 1, 2018

Schedule of Prospective Accounting Standards, Not Yet Effective Or Adopted

Table 2.2 shows the relevant new amendments to accounting standards, which are not yet effective or adopted.



	Table	2.2
Standard / Interpretation					Effective date
Standard / Interpretation	Amended Standards
	ASC 326		Financial Instruments - Credit Losses
			•	ASU 2016-13 - Measurement of Credit Losses on Financial Instruments	January 1, 2020
	ASC 820		Fair Value Measurement
			•	ASU 2018-13 - Changes to the Disclosure Requirements for Fair Value Measurements	January 1, 2020
	ASC 715		Compensation - Retirement Benefits
			•	ASU 2018-14 - Changes to the Disclosure Requirements for Defined Benefit Plans	January 1, 2021

Debt (Tables)

9 Months Ended

Sep. 30, 2018

Debt Disclosure [Abstract]

Long-term debt

The par value of our long-term debt obligations and their aggregate carrying values as of September 30, 2018 and December 31, 2017 are presented in table 3.1 below.



	Table	3.1
Long-term debt obligations	(In millions)		September 30, 2018			December 31, 2017
	FHLB Advance		$	155.0		$	155.0
	5.75% Senior Notes		425.0			425.0
	9% Convertible Junior Subordinated Debentures ⁽¹⁾		256.9			256.9
	Long-term debt, par value		836.9			836.9
	Debt issuance costs		(5.6		)	(6.5		)
	Long-term debt, carrying value		$	831.3		$	830.4

⁽¹⁾

Interest payments made

Table 3.2 below presents interest payments on our debt obligations.



	Table	3.2
Interest payments on debt obligations			Nine Months Ended September 30,
	(In millions)		2018		2017
	Revolving credit facility		$	0.5	$	0.5
	FHLB Advance		2.3		2.2
	5% Convertible Senior Notes		—		3.6
	2% Convertible Senior Notes		—		2.1
	5.75% Senior Notes		24.4		25.1
	9% Convertible Junior Subordinated Debentures		11.6		11.6
	Total interest payments		$	38.8	$	45.1

Reinsurance (Tables)

9 Months Ended

Sep. 30, 2018

Reinsurance Disclosures [Abstract]

Effect of reinsurance agreement

The effect of all of our reinsurance agreements on premiums earned and losses incurred is shown in table 4.1 below.



	Table	4.1
Effect of Reinsurance			Three Months Ended September 30,						Nine Months Ended September 30,
	(In thousands)		2018			2017			2018			2017
	Premiums earned:
	Direct		$	275,044		$	268,709		$	808,531		$	789,317
	Assumed		709			312			936			472
	Ceded		(25,327		)	(31,938		)	(79,970		)	(92,467		)
	Net premiums earned		$	250,426		$	237,083		$	729,497		$	697,322

	Losses incurred:
	Direct		$	(2,081	)	$	35,313		$	12,642		$	99,122
	Assumed		55			(97		)	45			69
	Ceded		508			(5,469		)	(3,810		)	(14,486		)
	Losses incurred, net		$	(1,518	)	$	29,747		$	8,877		$	84,705

Effect of quota share reinsurance agreements on premiums earned and losses incurred

Table 4.2 below presents a summary of our quota share reinsurance agreements, excluding captive agreements (which were immaterial), for the three and nine months ended September 30, 2018 and 2017.



	Table	4.2
Quota share reinsurance			Three Months Ended September 30,					Nine Months Ended September 30,
Quota share reinsurance	(In thousands)		2018			2017		2018		2017
	Ceded premiums written and earned, net of profit commission ⁽¹⁾		$	25,248		$	30,880	$	79,716	$	88,692
	Ceded losses incurred		(522		)	5,879		3,531		14,990
	Ceding commissions ⁽²⁾		12,983			12,500		38,268		36,751
	Profit commission		39,664			31,621		111,622		95,063


⁽¹⁾	Under our QSR Transactions, premiums are ceded on an earned and received basis as defined in the agreements.


⁽²⁾	Ceding commissions are reported within Other underwriting and operating expenses, net on the consolidated statements of operations.

Earnings per Share (Tables)

9 Months Ended

Sep. 30, 2018

Earnings Per Share [Abstract]

Calculation of earnings (loss) per share

Table 6.1 reconciles the numerators and denominators used to calculate basic and diluted EPS.



	Table	6.1
Earnings per share			Three Months Ended September 30,				Nine Months Ended September 30,
Earnings per share	(In thousands, except per share data)		2018		2017		2018		2017
	Basic earnings per share:
	Net income		$	181,900	$	120,027	$	512,351	$	328,447
	Weighted average common shares outstanding - basic		362,180		370,586		367,190		359,613
	Basic earnings per share		$	0.50	$	0.32	$	1.40	$	0.91

	Diluted earnings per share:
	Net income		$	181,900	$	120,027	$	512,351	$	328,447
	Interest expense, net of tax ⁽¹⁾:
	2% Convertible Senior Notes		—		—		—		907
	5% Convertible Senior Notes		—		—		—		1,709
	9% Convertible Junior Subordinated Debentures		4,566		3,757		13,698		11,270
	Diluted income available to common shareholders		$	186,466	$	123,784	$	526,049	$	342,333

	Weighted average common shares outstanding - basic		362,180		370,586		367,190		359,613
	Effect of dilutive securities:
	Unvested RSUs		1,697		1,473		1,547		1,367
	2% Convertible Senior Notes		—		—		—		11,119
	5% Convertible Senior Notes		—		—		—		4,743
	9% Convertible Junior Subordinated Debentures		19,028		19,028		19,028		19,028
	Weighted average common shares outstanding - diluted		382,905		391,087		387,765		395,870
	Diluted earnings per share		$	0.49	$	0.32	$	1.36	$	0.86


⁽¹⁾	The periods ended September 30, 2018 and 2017 were tax-effected at a rate of 21% and 35%, respectively.

Investments (Tables)

9 Months Ended

Sep. 30, 2018

Investments [Abstract]

Amortized cost, gross unrealized gains and losses and fair value of fixed income securities



	Table	7.1a
Details of fixed income securities by category - current year			September 30, 2018
	(In thousands)		Amortized Cost		Gross Unrealized Gains		Gross Unrealized (Losses) ⁽¹⁾			Fair Value
	U.S. Treasury securities and obligations of U.S. government corporations and agencies		$	179,395	$	174	$	(3,353	)	$	176,216
	Obligations of U.S. states and political subdivisions		1,738,417		17,797		(21,608		)	1,734,606
	Corporate debt securities		2,296,218		1,152		(42,305		)	2,255,065
	Asset backed securities (“ABS”)		71,481		—		(546		)	70,935
	Residential mortgage backed securities (“RMBS”)		166,522		35		(11,594		)	154,963
	Commercial mortgage backed securities (“CMBS”)		281,980		214		(11,974		)	270,220
	Collateralized loan obligations (“CLO”)		307,998		67		(458		)	307,607
	Total fixed income securities		5,042,011		19,439		(91,838		)	4,969,612



	Table	7.1b
Details of fixed income securities by category - prior year-end			December 31, 2017
	(In thousands)		Amortized Cost		Gross Unrealized Gains		Gross Unrealized (Losses) ⁽¹⁾			Fair Value
	U.S. Treasury securities and obligations of U.S. government corporations and agencies		$	179,850	$	274	$	(1,278	)	$	178,846
	Obligations of U.S. states and political subdivisions		2,105,063		56,210		(8,749		)	2,152,524
	Corporate debt securities		2,065,475		10,532		(9,169		)	2,066,838
	ABS		4,925		—		(2		)	4,923
	RMBS		189,153		60		(7,364		)	181,849
	CMBS		301,014		1,204		(4,906		)	297,312
	CLOs		100,798		304		(79		)	101,023
	Total fixed income securities		4,946,278		68,584		(31,547		)	4,983,315


⁽¹⁾	At September 30, 2018 and December 31, 2017, there were no other-than-temporary impairment losses recorded in other comprehensive income.

Amortized cost and fair values of fixed income securities by contractual maturity



	Table	7.2
Fixed income securities maturity schedule			September 30, 2018
	(In thousands)		Amortized Cost		Fair Value
	Due in one year or less		$	511,087	$	509,952
	Due after one year through five years		1,552,123		1,526,802
	Due after five years through ten years		940,185		918,757
	Due after ten years		1,210,635		1,210,376
			$	4,214,030	$	4,165,887

	ABS		71,481		70,935
	RMBS		166,522		154,963
	CMBS		281,980		270,220
	CLOs		307,998		307,607
	Total as of September 30, 2018		$	5,042,011	$	4,969,612

Cost and fair value of investments in equity securities



	Table	7.3a
Details of equity security investments - current year			September 30, 2018
	(In thousands)		Cost		Gross Gains		Gross Losses			Fair Value
	Equity securities		$	4,134	$	3,667	$	(81	)	$	7,720



	Table	7.3b
Details of equity security investments - prior year-end			December 31, 2017
	(In thousands)		Cost		Gross Gains		Gross Losses			Fair Value
	Equity securities		$	7,223	$	39	$	(16	)	$	7,246

Aging of the fair values of securities in an unrealized loss position



	Table	7.4a
Investments unrealized losses - current year			September 30, 2018
			Less Than 12 Months					12 Months or Greater					Total
	(In thousands)		Fair Value		Unrealized Losses			Fair Value		Unrealized Losses			Fair Value		Unrealized Losses
	U.S. Treasury securities and obligations of U.S. government corporations and agencies		$	89,759	$	(583	)	$	78,769	$	(2,770	)	$	168,528	$	(3,353	)
	Obligations of U.S. states and political subdivisions		643,147		(12,356		)	245,763		(9,252		)	888,910		(21,608		)
	Corporate debt securities		1,782,640		(29,184		)	299,549		(13,121		)	2,082,189		(42,305		)
	ABS		70,935		(546		)	—		—			70,935		(546		)
	RMBS		4,930		(183		)	149,648		(11,411		)	154,578		(11,594		)
	CMBS		81,972		(1,763		)	160,039		(10,211		)	242,011		(11,974		)
	CLOs		201,700		(458		)	—		—			201,700		(458		)
	Total		$	2,875,083	$	(45,073	)	$	933,768	$	(46,765	)	$	3,808,851	$	(91,838	)



	Table	7.4b
Investments unrealized losses - prior year-end			December 31, 2017
			Less Than 12 Months					12 Months or Greater					Total
	(In thousands)		Fair Value		Unrealized Losses			Fair Value		Unrealized Losses			Fair Value		Unrealized Losses
	U.S. Treasury securities and obligations of U.S. government corporations and agencies		$	144,042	$	(796	)	$	31,196	$	(482	)	$	175,238	$	(1,278	)
	Obligations of U.S. states and political subdivisions		505,311		(3,624		)	211,684		(5,125		)	716,995		(8,749		)
	Corporate debt securities		932,350		(4,288		)	200,716		(4,881		)	1,133,066		(9,169		)
	ABS		4,923		(2		)	—		—			4,923		(2		)
	RMBS		14,979		(280		)	166,329		(7,084		)	181,308		(7,364		)
	CMBS		51,096		(358		)	138,769		(4,548		)	189,865		(4,906		)
	CLOs		14,243		(7		)	3,568		(72		)	17,811		(79		)
	Equity securities		226		(2		)	431		(14		)	657		(16		)
	Total		$	1,667,170	$	(9,357	)	$	752,693	$	(22,206	)	$	2,419,863	$	(31,563	)

Fair Value Measurements (Tables)

9 Months Ended

Sep. 30, 2018

Fair Value Disclosures [Abstract]

Fair value measurements for items measured at fair value



	Table	8.1a
Fair value hierarchy - current year			September 30, 2018
Fair value hierarchy - current year	(In thousands)		Total Fair Value		Quoted Prices in Active Markets for Identical Assets (Level 1)		Significant Other Observable Inputs (Level 2)		Significant Unobservable Inputs (Level 3)
	U.S. Treasury securities and obligations of U.S. government corporations and agencies		$	176,216	$	29,584	$	146,632	$	—
	Obligations of U.S. states and political subdivisions		1,734,606		—		1,734,529		77
	Corporate debt securities		2,255,065		—		2,255,065		—
	ABS		70,935		—		70,935		—
	RMBS		154,963		—		154,963		—
	CMBS		270,220		—		270,220		—
	CLOs		307,607		—		307,607		—
	Total fixed income securities		4,969,612		29,584		4,939,951		77
	Equity securities		7,720		2,889		—		4,831
	Total investments at fair value		$	4,977,332	$	32,473	$	4,939,951	$	4,908
	Real estate acquired ⁽¹⁾		$	12,339	$	—	$	—	$	12,339



	Table	8.1b
Fair value hierarchy - prior year-end			December 31, 2017
Fair value hierarchy - prior year-end	(In thousands)		Total Fair Value		Quoted Prices in Active Markets for Identical Assets (Level 1)		Significant Other Observable Inputs (Level 2)		Significant Unobservable Inputs (Level 3)
	U.S. Treasury securities and obligations of U.S. government corporations and agencies		$	178,846	$	81,598	$	97,248	$	—
	Obligations of U.S. states and political subdivisions		2,152,524		—		2,152,253		271
	Corporate debt securities		2,066,838		—		2,066,838		—
	ABS		4,923		—		4,923		—
	RMBS		181,849		—		181,849		—
	CMBS		297,312		—		297,312		—
	CLOs		101,023		—		101,023		—
	Total fixed income securities		4,983,315		81,598		4,901,446		271
	Equity securities ⁽²⁾		7,246		2,978		—		4,268
	Total investments at fair value		$	4,990,561	$	84,576	$	4,901,446	$	4,539
	Real estate acquired ⁽¹⁾		$	12,713	$	—	$	—	$	12,713


⁽¹⁾	Real estate acquired through claim settlement, which is held for sale, is reported in Other assets on the consolidated balance sheets.


⁽²⁾	Equity securities in Level 3 are carried at cost, which approximates fair value. See “Reconciliations of Level 3 assets” below for information regarding a change in presentation of amounts previously included in Level 3 Equity securities.

Reconciliation of beginning and ending balance for assets and liabilities measured at fair value with significant unobservable inputs (level 3)



	Table	8.2a
Development of assets and liabilities classified within level 3 - current year quarter			Three Months Ended September 30, 2018
	(In thousands)		Debt Securities			Equity Securities		Total Investments			Real Estate Acquired
	Balance at June 30, 2018		$	192		$	1,168	$	1,360		$	13,321
	Total realized gains (losses):
	Included in earnings and reported as net realized investment gains		—			3,663		3,663			—
	Included in earnings and reported as losses incurred, net		—			—		—			(450		)
	Purchases		—			—		—			7,979
	Sales		(115		)	—		(115		)	(8,511		)
	Balance at September 30, 2018		$	77		$	4,831	$	4,908		$	12,339



	Table	8.2b
Development of assets and liabilities classified within level 3 - prior year quarter			Three Months Ended September 30, 2017
	(In thousands)		Debt Securities			Equity Securities		Total Investments			Real Estate Acquired
	Balance at June 30, 2017		$	577		$	4,268	$	4,845		$	10,271
	Total realized gains (losses):
	Included in earnings and reported as losses incurred, net		—			—		—			(592		)
	Purchases		—			—		—			8,881
	Sales		(197		)	—		(197		)	(6,832		)
	Balance at September 30, 2017		$	380		$	4,268	$	4,648		$	11,728



	Table	8.3a
Development of assets and liabilities classified within level 3 - current year to date			Nine Months Ended September 30, 2018
	(In thousands)		Debt Securities			Equity Securities			Total Investments			Real Estate Acquired
	Balance at December 31, 2017		$	271		$	4,268		$	4,539		$	12,713
	Transfers out of Level 3		—			(3,100		)	(3,100		)	—
	Total realized gains (losses):
	Included in earnings and reported as net realized investment gains		—			3,663			3,663			—
	Included in earnings and reported as losses incurred, net		—			—			—			(1,104		)
	Purchases		—			—			—			24,742
	Sales		(194		)	—			(194		)	(24,012		)
	Balance at September 30, 2018		$	77		$	4,831		$	4,908		$	12,339



	Table	8.3b
Development of assets and liabilities classified within level 3 - prior year to date			Nine Months Ended September 30, 2017
	(In thousands)		Debt Securities			Equity Securities		Total Investments			Real Estate Acquired
	Balance at December 31, 2016		$	691		$	4,268	$	4,959		$	11,748
	Total realized gains (losses):
	Included in earnings and reported as losses incurred, net		—			—		—			(818		)
	Purchases		—			—		—			26,985
	Sales		(311		)	—		(311		)	(26,187		)
	Balance at September 30, 2017		$	380		$	4,268	$	4,648		$	11,728

Carrying value and fair value of debt

Table 8.4 presents the carrying value and fair value of our financial liabilities disclosed, but not carried, at fair value at September 30, 2018 and December 31, 2017. The fair values of our 5.75% Senior Notes and 9% Convertible Junior Subordinated Debentures were based on observable market prices. The fair value of the FHLB Advance was estimated using cash flows discounted at current incremental borrowing rates for similar borrowing arrangements. In all cases the fair values of the financial liabilities below are categorized as Level 2.



	Table	8.4
Fair value measurements - liabilities			September 30, 2018				December 31, 2017
	(In thousands)		Carrying Value		Fair Value		Carrying Value		Fair Value
	FHLB Advance		$	155,000	$	148,288	$	155,000	$	152,124
	5.75% Senior Notes		419,425		445,430		418,560		465,473
	9% Convertible Junior Subordinated Debentures		256,872		347,458		256,872		353,507
	Total financial liabilities		$	831,297	$	941,176	$	830,432	$	971,104

Other Comprehensive Income (Tables)

9 Months Ended

Sep. 30, 2018

Comprehensive Income (Loss), Net of Tax, Attributable to Parent [Abstract]

Other comprehensive income



	Table	9.1
Components of other comprehensive (loss) income			Three Months Ended September 30,						Nine Months Ended September 30,
	(In thousands)		2018			2017			2018			2017
	Net unrealized investment (losses) gains arising during the period		$	(15,288	)	$	17,761		$	(109,433	)	$	76,022
	Income tax benefit (expense)		3,211			(6,217		)	22,981			(26,608		)
	Net of taxes		(12,077		)	11,544			(86,452		)	49,414

	Net changes in benefit plan assets and obligations		558			(226		)	1,674			(680		)
	Income tax (expense) benefit		(118		)	79			(352		)	238
	Net of taxes		440			(147		)	1,322			(442		)

	Net changes in unrealized foreign currency translation adjustment		—			—			—			45
	Income tax (expense)		—			—			—			(14		)
	Net of taxes		—			—			—			31

	Total other comprehensive (loss) income		(14,730		)	17,535			(107,759		)	75,387
	Total income tax benefit (expense)		3,093			(6,138		)	22,629			(26,384		)
	Total other comprehensive (loss) income, net of tax		$	(11,637	)	$	11,397		$	(85,130	)	$	49,003

Reclassification out of accumulated other comprehensive income



	Table	9.2
Reclassifications from AOCL			Three Months Ended September 30,						Nine Months Ended September 30,
	(In thousands)		2018			2017			2018			2017
	Reclassification adjustment for net realized (losses) ⁽¹⁾		$	(2,567	)	$	(427	)	$	(6,279	)	$	(2,566	)
	Income tax benefit		539			150			1,318			898
	Net of taxes		(2,028		)	(277		)	(4,961		)	(1,668		)

	Reclassification adjustment related to benefit plan assets and obligations ⁽²⁾		(558		)	226			(1,674		)	680
	Income tax benefit (expense)		118			(79		)	352			(238		)
	Net of taxes		(440		)	147			(1,322		)	442

	Total reclassifications		(3,125		)	(201		)	(7,953		)	(1,886		)
	Total income tax benefit		657			71			1,670			660
	Total reclassifications, net of tax		$	(2,468	)	$	(130	)	$	(6,283	)	$	(1,226	)


⁽¹⁾	Increases (decreases) Net realized investment (losses) gains on the consolidated statements of operations.


⁽²⁾	Decreases (increases) Other underwriting and operating expenses, net on the consolidated statements of operations.

Accumulated other comprehensive income (loss)

A rollforward of AOCL for the nine months ended September 30, 2018, including amounts reclassified from AOCL, are included in table 9.3 below.



	Table	9.3
Rollforward of AOCL			Nine Months Ended September 30, 2018
Rollforward of AOCL	(In thousands)		Net unrealized gains and losses on available-for-sale securities			Net benefit plan assets and obligations recognized in shareholders' equity			Total AOCL
	Balance, December 31, 2017, net of tax		$	29,257		$	(73,058	)	$	(43,801	)
	Other comprehensive income before reclassifications		(91,413		)	—			(91,413		)
	Less: Amounts reclassified from AOCL		(4,961		)	(1,322		)	(6,283		)
	Balance, September 30, 2018, net of tax		$	(57,195	)	$	(71,736	)	$	(128,931	)

Benefit Plans (Tables)

9 Months Ended

Sep. 30, 2018

Retirement Benefits [Abstract]

Components of net periodic benefit cost



	Table	10.1
Components of net periodic benefit cost			Three Months Ended September 30,
Components of net periodic benefit cost			Pension and Supplemental Executive Retirement Plans						Other Postretirement Benefit Plans
	(In thousands)		2018			2017			2018			2017
	Service cost		$	2,633		$	2,389		$	290		$	203
	Interest cost		3,774			3,869			208			176
	Expected return on plan assets		(5,563		)	(5,025		)	(1,590		)	(1,312		)
	Amortization of net actuarial losses/(gains)		1,734			1,543			(62		)	—
	Amortization of prior service cost/(credit)		(88		)	(107		)	(1,026		)	(1,662		)
	Net periodic benefit cost (benefit)		$	2,490		$	2,669		$	(2,180	)	$	(2,595	)



	Table	10.2
Components of net periodic benefit cost			Nine Months Ended September 30,
Components of net periodic benefit cost			Pension and Supplemental Executive Retirement Plans						Other Postretirement Benefit Plans
	(In thousands)		2018			2017			2018			2017
	Service cost		$	7,898		$	7,167		$	870		$	610
	Interest cost		11,321			11,606			625			529
	Expected return on plan assets		(16,688		)	(15,074		)	(4,769		)	(3,936		)
	Amortization of net actuarial losses/(gains)		5,203			4,627			(187		)	—
	Amortization of prior service cost/(credit)		(263		)	(320		)	(3,078		)	(4,987		)
	Net periodic benefit cost (benefit)		$	7,471		$	8,006		$	(6,539	)	$	(7,784	)

Loss Reserves (Tables)

9 Months Ended

Sep. 30, 2018

Insurance Loss Reserves [Abstract]

Reconciliation of beginning and ending loss reserves

Table 12.1 provides a reconciliation of beginning and ending loss reserves as of and for the nine months ended September 30, 2018 and 2017.



	Table	12.1
Development of reserves for losses and loss adjustment expenses			Nine months ended September 30,
	(In thousands)		2018			2017
	Reserve at beginning of period		$	985,635		$	1,438,813
	Less reinsurance recoverable		48,474			50,493
	Net reserve at beginning of period		937,161			1,388,320

	Losses incurred:
	Losses and LAE incurred in respect of delinquency notices received in:
	Current year		155,808			219,485
	Prior years ⁽¹⁾		(146,931		)	(134,780		)
	Total losses incurred		8,877			84,705

	Losses paid:
	Losses and LAE paid in respect of delinquency notices received in:
	Current year		2,449			5,474
	Prior years		257,808			407,977
	Reinsurance terminations		(1,984		)	301
	Total losses paid		258,273			413,752
	Net reserve at end of period		687,765			1,059,273
	Plus reinsurance recoverables		33,281			45,878
	Reserve at end of period		$	721,046		$	1,105,151


⁽¹⁾	A negative number for prior year losses incurred indicates a redundancy of prior year loss reserves. See the following table for more information about prior year loss development.

Prior year development of the reserves

The prior year development of the reserves in the first nine months of 2018 and 2017 is reflected in table 12.2 below.



	Table	12.2
Reserve development on previously received delinquencies			Nine months ended September 30,
	(in millions)		2018			2017
	Decrease in estimated claim rate on primary defaults		$	(184	)	$	(138	)
	Increase in estimated severity on primary defaults		22			(2		)
	Change in estimates related to pool reserves, LAE reserves and reinsurance		15			5
	Total prior year loss development ⁽¹⁾		$	(147	)	$	(135	)


⁽¹⁾	A negative number for prior year loss development indicates a redundancy of prior year loss reserves.

Rollforward of primary delinquent inventory



	Table	12.3
Delinquent inventory rollforward			Three Months Ended September 30,				Nine Months Ended September 30,
			2018		2017		2018		2017
	Delinquent inventory at beginning of period		36,037		41,317		46,556		50,282
	New notices		13,569		15,950		40,351		45,352
	Cures		(14,197	)	(13,546	)	(47,620	)	(45,382	)
	Paids (including those charged to a deductible or captive)		(1,374	)	(2,195	)	(4,446	)	(7,403	)
	Rescissions and denials		(56	)	(82	)	(200	)	(277	)
	Other items removed from inventory		(581	)	(209	)	(1,243	)	(1,337	)
	Delinquent inventory at end of period		33,398		41,235		33,398		41,235

Aging of the primary delinquent inventory

Table 12.4 below shows the number of consecutive months a borrower is delinquent.



	Table	12.4
Delinquent inventory - consecutive months in default			September 30, 2018			December 31, 2017			September 30, 2017
	3 months or less		9,484	28	%	17,119	37	%	11,331	27	%
	4-11 months		9,564	29	%	12,050	26	%	11,092	27	%
	12 months or more ^{(1) (2)}		14,350	43	%	17,387	37	%	18,812	46	%
	Total primary delinquent inventory		33,398	100	%	46,556	100	%	41,235	100	%

	Primary claims received inventory included in ending delinquent inventory:		766	2	%	954	2	%	1,063	3	%


⁽¹⁾	Approximately 39%, 45%, and 45% of the primary delinquent inventory delinquent for 12 consecutive months or more has been delinquent for at least 36 consecutive months as of September 30, 2018, December 31, 2017, and September 30, 2017, respectively.


⁽²⁾	The majority of items removed from our delinquent inventory due to commutations of NPLs during the nine months ended September 30, 2018 were delinquent for 12 consecutive months or more as of December 31, 2017.

Number of payments delinquent

Table 12.5 below shows the number of payments that a borrower is delinquent.



	Table	12.5
Delinquent inventory - number of payments delinquent			September 30, 2018			December 31, 2017			September 30, 2017
	3 payments or less		14,813	44	%	21,678	46	%	16,916	41	%
	4-11 payments		9,156	28	%	12,446	27	%	10,583	26	%
	12 payments or more ^{(1) (2)}		9,429	28	%	12,432	27	%	13,736	33	%
	Total primary delinquent inventory		33,398	100	%	46,556	100	%	41,235	100	%


⁽¹⁾	Approximately 39%, 43%, and 43% of the primary delinquent inventory with 12 payments or more delinquent has at least 36 payments delinquent as of September 30, 2018, December 31, 2017, and September 30, 2017, respectively.


⁽²⁾	The majority of items removed from our delinquent inventory due to commutations of NPLs during the nine months ended September 30, 2018 had 12 or more payments delinquent as of December 31, 2017.

Share-Based Compensation (Tables)

9 Months Ended

Sep. 30, 2018

Disclosure of Compensation Related Costs, Share-based Payments [Abstract]

Schedule of stock-based compensation, activity

Table 14.1 shows the number of shares granted to employees and the weighted average fair value per share during the periods presented (shares in thousands).



	Table	14.1
Restricted stock grants			Nine months ended September 30,
Restricted stock grants			2018			2017
			Shares Granted	Weighted Average Share Fair Value		Shares Granted	Weighted Average Share Fair Value
	RSUs subject to performance conditions		1,239	$	15.80	1,237	$	10.41
	RSUs subject only to service conditions		447	15.39		395	10.41

Debt - Summary of Debt Obligations (Details) - USD ($) $ in Millions	Sep. 30, 2018	Dec. 31, 2017
Debt Instrument [Line Items]
Long-term debt, par value	$ 836.9	$ 836.9
Debt issuance costs	(5.6)	(6.5)
Long-term debt, carrying value	831.3	830.4
FHLB Advance
Debt Instrument [Line Items]
Long-term debt, par value	155.0	155.0
Senior Notes \| 5.75% Senior Notes Due 2023
Debt Instrument [Line Items]
Long-term debt, par value	$ 425.0	425.0
Stated interest rate	5.75%
9% Convertible Junior Subordinated Debentures
Debt Instrument [Line Items]
Long-term debt, par value	$ 256.9	$ 256.9
Stated interest rate	9.00%

Debt - Narrative (Details)	9 Months Ended
Debt - Narrative (Details)	Sep. 30, 2018 $ / shares
9% Convertible Junior Subordinated Debentures
Debt Instrument [Line Items]
Conversion rate (in shares per $1,000 note)	0.0740741
Convertible debt, conversion price (in dollars per share)	$ 13.50
Period preceding election to convert (in days)	5 days
Stated interest rate	9.00%
Senior Notes \| 5.75% Senior Notes Due 2023
Debt Instrument [Line Items]
Stated interest rate	5.75%

Debt - Summary of Interest Paid (Details) - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017
Debt Instrument [Line Items]
Total interest payments	$ 38.8	$ 45.1
Line of Credit \| Revolving Credit Facility
Debt Instrument [Line Items]
Total interest payments	0.5	0.5
FHLB Advance
Debt Instrument [Line Items]
Total interest payments	2.3	2.2
5% Convertible Senior Notes
Debt Instrument [Line Items]
Total interest payments	0.0	$ 3.6
Stated interest rate		5.00%
2% Convertible Senior Notes
Debt Instrument [Line Items]
Total interest payments	0.0	$ 2.1
Stated interest rate		2.00%
Senior Notes \| 5.75% Senior Notes Due 2023
Debt Instrument [Line Items]
Total interest payments	$ 24.4	$ 25.1
Stated interest rate	5.75%
9% Convertible Junior Subordinated Debentures
Debt Instrument [Line Items]
Total interest payments	$ 11.6	$ 11.6
Stated interest rate	9.00%

Reinsurance - Summary of Premiums Earned and Losses Incurred (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Premiums earned:
Direct	$ 275,044	$ 268,709	$ 808,531	$ 789,317
Assumed	709	312	936	472
Ceded	(25,327)	(31,938)	(79,970)	(92,467)
Net premiums earned	250,426	237,083	729,497	697,322
Losses incurred:
Direct	(2,081)	35,313	12,642	99,122
Assumed	55	(97)	45	69
Ceded	508	(5,469)	(3,810)	(14,486)
Losses incurred, net	$ (1,518)	$ 29,747	$ 8,877	$ 84,705

Reinsurance - Narrative (Details) - USD ($)	9 Months Ended
Reinsurance - Narrative (Details) - USD ($)	Sep. 30, 2018	Dec. 31, 2017	Sep. 30, 2017	Dec. 31, 2016
Effects of Reinsurance [Line Items]
Reinsurance recoverable on loss reserves	$ 33,281,000	$ 48,474,000	$ 45,878,000	$ 50,493,000
Quota Share Reinsurance Agreement, 2018
Effects of Reinsurance [Line Items]
Contingent termination fee	$ 0
Threshold for private mortgage insurer eligibility requirements for termination election (less than) (as a percent)	90.00%
Quota share for all policies covered (as a percent)	30.00%
Ceding commission, percentage (as a percent)	20.00%
Loss ratio threshold for profit commissions (as a percent)	62.00%
Quota Share Reinsurance Agreement, 2017
Effects of Reinsurance [Line Items]
Contingent termination fee	$ 0
Threshold for private mortgage insurer eligibility requirements for termination election (less than) (as a percent)	90.00%
Quota share for all policies covered (as a percent)	30.00%
Ceding commission, percentage (as a percent)	20.00%
Loss ratio threshold for profit commissions (as a percent)	60.00%
Quota Share Reinsurance Agreement, 2015
Effects of Reinsurance [Line Items]
Contingent termination fee	$ 0
Threshold for private mortgage insurer eligibility requirements for termination election (less than) (as a percent)	90.00%
Quota share for all policies covered (as a percent)	30.00%
Ceding commission, percentage (as a percent)	20.00%
Loss ratio threshold for profit commissions (as a percent)	60.00%
Quota Share Reinsurance Agreements, Excluding Captive Agreements
Effects of Reinsurance [Line Items]
Reinsurance recoverable on loss reserves	$ 33,100,000	$ 39,300,000

Reinsurance - Summary of Quota Reinsurance Arrangements (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Effects of Reinsurance [Line Items]
Ceded losses incurred	$ (508)	$ 5,469	$ 3,810	$ 14,486
Quota Share Reinsurance Agreements, Excluding Captive Agreements
Effects of Reinsurance [Line Items]
Ceded premiums written and earned, net of profit commission	25,248	30,880	79,716	88,692
Ceded losses incurred	(522)	5,879	3,531	14,990
Ceding commissions	12,983	12,500	38,268	36,751
Profit commission	$ 39,664	$ 31,621	$ 111,622	$ 95,063

Litigation and Contingencies (Details) - USD ($) $ in Millions	9 Months Ended	12 Months Ended
	Sep. 30, 2018	Dec. 31, 2017
Commitments and Contingencies Disclosure [Abstract]
Average paid claim reduction due to curtailments (as a percent)	6.30%	5.60%
Maximum exposure associated with other discussions and legal proceedings	$ 286

Earnings per Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Basic earnings per share:
Net income	$ 181,900	$ 120,027	$ 512,351	$ 328,447
Weighted average common shares outstanding - basic (in shares)	362,180	370,586	367,190	359,613
Basic earnings per share (in dollars per share)	$ 0.50	$ 0.32	$ 1.40	$ 0.91
Diluted earnings per share:
Net income	$ 181,900	$ 120,027	$ 512,351	$ 328,447
Diluted income available to common shareholders	$ 186,466	$ 123,784	$ 526,049	$ 342,333
Weighted average common shares outstanding - basic (in shares)	362,180	370,586	367,190	359,613
Effect of dilutive securities:
Weighted average common shares outstanding - diluted (in shares)	382,905	391,087	387,765	395,870
Diluted earnings per share (in dollars per share)	$ 0.49	$ 0.32	$ 1.36	$ 0.86
Effective income tax rate			21.00%	35.00%
2% Convertible Senior Notes
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Stated interest rate		2.00%		2.00%
Diluted earnings per share:
Dilutive securities	$ 0	$ 0	$ 0	$ 907
Effect of dilutive securities:
Dilutive securities (in shares)	0	0	0	11,119
5% Convertible Senior Notes
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Stated interest rate		5.00%		5.00%
Diluted earnings per share:
Dilutive securities	$ 0	$ 0	$ 0	$ 1,709
Effect of dilutive securities:
Dilutive securities (in shares)	0	0	0	4,743
9% Convertible Junior Subordinated Debentures
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Stated interest rate	9.00%		9.00%
Diluted earnings per share:
Dilutive securities	$ 4,566	$ 3,757	$ 13,698	$ 11,270
Effect of dilutive securities:
Dilutive securities (in shares)	19,028	19,028	19,028	19,028
Unvested RSUs
Effect of dilutive securities:
Unvested RSUs (in shares)	1,697	1,473	1,547	1,367

Investments (Details)	3 Months Ended		9 Months Ended		12 Months Ended
Investments (Details)	Sep. 30, 2018 USD ($) security	Sep. 30, 2017 USD ($)	Sep. 30, 2018 USD ($) security	Sep. 30, 2017 USD ($)	Dec. 31, 2017 USD ($) security
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	$ 5,042,011,000		$ 5,042,011,000		$ 4,946,278,000
Fair Value	4,969,612,000		4,969,612,000		4,983,315,000
Other than Temporary Impairment Losses, Portion in Other Comprehensive Income			0		0
Assets held by insurance regulators	13,400,000		13,400,000		$ 13,600,000
Proceeds from sales of fixed income securities			338,900,000	$ 233,200,000
Gross realized gains			400,000	900,000
Gross realized losses			3,300,000	1,100,000
Net impairment losses recognized in earnings	500,000	$ 0	$ 1,800,000	$ 0
Federal Home Loan Bank advances, collateral, value of principal, percent (as a percent)			102.00%
FHLB advance collateral	$ 166,100,000		$ 166,100,000
Number of securities in unrealized loss position (in securities) \| security	810		810		586
Total fixed income securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	$ 5,042,011,000		$ 5,042,011,000		$ 4,946,278,000
Gross Unrealized Gains	19,439,000		19,439,000		68,584,000
Gross Unrealized Losses	(91,838,000)		(91,838,000)		(31,547,000)
Fair Value	4,969,612,000		4,969,612,000		4,983,315,000
U.S. Treasury securities and obligations of U.S. government corporations and agencies
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	179,395,000		179,395,000		179,850,000
Gross Unrealized Gains	174,000		174,000		274,000
Gross Unrealized Losses	(3,353,000)		(3,353,000)		(1,278,000)
Fair Value	176,216,000		176,216,000		178,846,000
Obligations of U.S. states and political subdivisions
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	1,738,417,000		1,738,417,000		2,105,063,000
Gross Unrealized Gains	17,797,000		17,797,000		56,210,000
Gross Unrealized Losses	(21,608,000)		(21,608,000)		(8,749,000)
Fair Value	1,734,606,000		1,734,606,000		2,152,524,000
Corporate debt securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	2,296,218,000		2,296,218,000		2,065,475,000
Gross Unrealized Gains	1,152,000		1,152,000		10,532,000
Gross Unrealized Losses	(42,305,000)		(42,305,000)		(9,169,000)
Fair Value	2,255,065,000		2,255,065,000		2,066,838,000
Asset backed securities (“ABS”)
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	71,481,000		71,481,000		4,925,000
Gross Unrealized Gains	0		0		0
Gross Unrealized Losses	(546,000)		(546,000)		(2,000)
Fair Value	70,935,000		70,935,000		4,923,000
Residential mortgage backed securities (“RMBS”)
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	166,522,000		166,522,000		189,153,000
Gross Unrealized Gains	35,000		35,000		60,000
Gross Unrealized Losses	(11,594,000)		(11,594,000)		(7,364,000)
Fair Value	154,963,000		154,963,000		181,849,000
Commercial mortgage backed securities (“CMBS”)
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	281,980,000		281,980,000		301,014,000
Gross Unrealized Gains	214,000		214,000		1,204,000
Gross Unrealized Losses	(11,974,000)		(11,974,000)		(4,906,000)
Fair Value	270,220,000		270,220,000		297,312,000
Collateralized loan obligations (“CLO”)
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	307,998,000		307,998,000		100,798,000
Gross Unrealized Gains	67,000		67,000		304,000
Gross Unrealized Losses	(458,000)		(458,000)		(79,000)
Fair Value	$ 307,607,000		$ 307,607,000		$ 101,023,000

Investments - Amortized Cost and Fair Values of Debt Securities (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Amortized Cost
Due in one year or less	$ 511,087
Due after one year through five years	1,552,123
Due after five years through ten years	940,185
Due after ten years	1,210,635
Total debt securities with single maturity date, amortized cost	4,214,030
Amortized Cost	5,042,011	$ 4,946,278
Fair Value
Due in one year or less	509,952
Due after one year through five years	1,526,802
Due after five years through ten years	918,757
Due after ten years	1,210,376
Total debt securities with single maturity date, fair value	4,165,887
Total at end of period	4,969,612	4,983,315
Asset backed securities (“ABS”)
Amortized Cost
Total debt securities without single maturity date, amortized cost	71,481
Amortized Cost	71,481	4,925
Fair Value
Total debt securities without single maturity date, fair value	70,935
Total at end of period	70,935	4,923
Residential mortgage backed securities (“RMBS”)
Amortized Cost
Total debt securities without single maturity date, amortized cost	166,522
Amortized Cost	166,522	189,153
Fair Value
Total debt securities without single maturity date, fair value	154,963
Total at end of period	154,963	181,849
Commercial mortgage backed securities (“CMBS”)
Amortized Cost
Total debt securities without single maturity date, amortized cost	281,980
Amortized Cost	281,980	301,014
Fair Value
Total debt securities without single maturity date, fair value	270,220
Total at end of period	270,220	297,312
Collateralized loan obligations (“CLO”)
Amortized Cost
Total debt securities without single maturity date, amortized cost	307,998
Amortized Cost	307,998	100,798
Fair Value
Total debt securities without single maturity date, fair value	307,607
Total at end of period	$ 307,607	$ 101,023

Investments - Equity Securities (Details) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2018	Dec. 31, 2017
Equity Securities, FV-NI, Gain (Loss) [Abstract]
Cost	$ 4,134
Gross Gains	3,667
Gross Losses	(81)
Fair Value	7,720
Unrealized Gain (Loss) on Equity Securities [Abstract]
Cost		$ 7,223
Gross Gains		39
Gross Losses		(16)
Fair Value		$ 7,246
Recognized net gains on equity securities still held	$ 3,600

Investments - Securities In Unrealized Loss Position (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Continuous Unrealized Loss Portion, Fair Value [Abstract]
Less Than 12 Months	$ 2,875,083
12 Months or Greater	933,768
Total	3,808,851
Continuous Unrealized Loss Portion, Unrealized Loses [Abstract]
Less Than 12 Months	(45,073)
12 Months or Greater	(46,765)
Total	(91,838)
Available-for-sale Securities, Continuous Unrealized Loss Position [Abstract]
Less Than 12 Months		$ 1,667,170
12 Months or Greater		752,693
Total		2,419,863
Other than Temporary Impairment Losses, Investments, Available-for-sale Securities, Reportable Items [Abstract]
Less Than 12 Months		(9,357)
12 Months or Greater		(22,206)
Total		(31,563)
U.S. Treasury securities and obligations of U.S. government corporations and agencies
Continuous Unrealized Loss Portion, Fair Value [Abstract]
Less Than 12 Months	89,759
12 Months or Greater	78,769
Total	168,528
Continuous Unrealized Loss Portion, Unrealized Loses [Abstract]
Less Than 12 Months	(583)
12 Months or Greater	(2,770)
Total	(3,353)
Available-for-sale Securities, Continuous Unrealized Loss Position [Abstract]
Less Than 12 Months		144,042
12 Months or Greater		31,196
Total		175,238
Other than Temporary Impairment Losses, Investments, Available-for-sale Securities, Reportable Items [Abstract]
Less Than 12 Months		(796)
12 Months or Greater		(482)
Total		(1,278)
Obligations of U.S. states and political subdivisions
Continuous Unrealized Loss Portion, Fair Value [Abstract]
Less Than 12 Months	643,147
12 Months or Greater	245,763
Total	888,910
Continuous Unrealized Loss Portion, Unrealized Loses [Abstract]
Less Than 12 Months	(12,356)
12 Months or Greater	(9,252)
Total	(21,608)
Available-for-sale Securities, Continuous Unrealized Loss Position [Abstract]
Less Than 12 Months		505,311
12 Months or Greater		211,684
Total		716,995
Other than Temporary Impairment Losses, Investments, Available-for-sale Securities, Reportable Items [Abstract]
Less Than 12 Months		(3,624)
12 Months or Greater		(5,125)
Total		(8,749)
Corporate debt securities
Continuous Unrealized Loss Portion, Fair Value [Abstract]
Less Than 12 Months	1,782,640
12 Months or Greater	299,549
Total	2,082,189
Continuous Unrealized Loss Portion, Unrealized Loses [Abstract]
Less Than 12 Months	(29,184)
12 Months or Greater	(13,121)
Total	(42,305)
Available-for-sale Securities, Continuous Unrealized Loss Position [Abstract]
Less Than 12 Months		932,350
12 Months or Greater		200,716
Total		1,133,066
Other than Temporary Impairment Losses, Investments, Available-for-sale Securities, Reportable Items [Abstract]
Less Than 12 Months		(4,288)
12 Months or Greater		(4,881)
Total		(9,169)
Asset backed securities (“ABS”)
Continuous Unrealized Loss Portion, Fair Value [Abstract]
Less Than 12 Months	70,935
12 Months or Greater	0
Total	70,935
Continuous Unrealized Loss Portion, Unrealized Loses [Abstract]
Less Than 12 Months	(546)
12 Months or Greater	0
Total	(546)
Available-for-sale Securities, Continuous Unrealized Loss Position [Abstract]
Less Than 12 Months		4,923
12 Months or Greater		0
Total		4,923
Other than Temporary Impairment Losses, Investments, Available-for-sale Securities, Reportable Items [Abstract]
Less Than 12 Months		(2)
12 Months or Greater		0
Total		(2)
Residential mortgage backed securities (“RMBS”)
Continuous Unrealized Loss Portion, Fair Value [Abstract]
Less Than 12 Months	4,930
12 Months or Greater	149,648
Total	154,578
Continuous Unrealized Loss Portion, Unrealized Loses [Abstract]
Less Than 12 Months	(183)
12 Months or Greater	(11,411)
Total	(11,594)
Available-for-sale Securities, Continuous Unrealized Loss Position [Abstract]
Less Than 12 Months		14,979
12 Months or Greater		166,329
Total		181,308
Other than Temporary Impairment Losses, Investments, Available-for-sale Securities, Reportable Items [Abstract]
Less Than 12 Months		(280)
12 Months or Greater		(7,084)
Total		(7,364)
Commercial mortgage backed securities (“CMBS”)
Continuous Unrealized Loss Portion, Fair Value [Abstract]
Less Than 12 Months	81,972
12 Months or Greater	160,039
Total	242,011
Continuous Unrealized Loss Portion, Unrealized Loses [Abstract]
Less Than 12 Months	(1,763)
12 Months or Greater	(10,211)
Total	(11,974)
Available-for-sale Securities, Continuous Unrealized Loss Position [Abstract]
Less Than 12 Months		51,096
12 Months or Greater		138,769
Total		189,865
Other than Temporary Impairment Losses, Investments, Available-for-sale Securities, Reportable Items [Abstract]
Less Than 12 Months		(358)
12 Months or Greater		(4,548)
Total		(4,906)
Collateralized loan obligations (“CLO”)
Continuous Unrealized Loss Portion, Fair Value [Abstract]
Less Than 12 Months	201,700
12 Months or Greater	0
Total	201,700
Continuous Unrealized Loss Portion, Unrealized Loses [Abstract]
Less Than 12 Months	(458)
12 Months or Greater	0
Total	$ (458)
Available-for-sale Securities, Continuous Unrealized Loss Position [Abstract]
Less Than 12 Months		14,243
12 Months or Greater		3,568
Total		17,811
Other than Temporary Impairment Losses, Investments, Available-for-sale Securities, Reportable Items [Abstract]
Less Than 12 Months		(7)
12 Months or Greater		(72)
Total		(79)
Equity securities
Available-for-sale Securities, Continuous Unrealized Loss Position [Abstract]
Less Than 12 Months		226
12 Months or Greater		431
Total		657
Other than Temporary Impairment Losses, Investments, Available-for-sale Securities, Reportable Items [Abstract]
Less Than 12 Months		(2)
12 Months or Greater		(14)
Total		$ (16)

Fair Value Measurements (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
U.S. Treasury securities and obligations of U.S. government corporations and agencies	$ 176,216	$ 178,846
Obligations of U.S. states and political subdivisions	1,734,606	2,152,524
Corporate debt securities	2,255,065	2,066,838
ABS	70,935	4,923
RMBS	154,963	181,849
CMBS	270,220	297,312
CLOs	307,607	101,023
Total fixed income securities	4,969,612	4,983,315
Equity securities	7,720	7,246
Total investments at fair value	4,977,332	4,990,561
Real estate acquired	12,339	12,713
Quoted Prices in Active Markets for Identical Assets (Level 1)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
U.S. Treasury securities and obligations of U.S. government corporations and agencies	29,584	81,598
Obligations of U.S. states and political subdivisions	0	0
Corporate debt securities	0	0
ABS	0	0
RMBS	0	0
CMBS	0	0
CLOs	0	0
Total fixed income securities	29,584	81,598
Equity securities	2,889	2,978
Total investments at fair value	32,473	84,576
Real estate acquired	0	0
Significant Other Observable Inputs (Level 2)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
U.S. Treasury securities and obligations of U.S. government corporations and agencies	146,632	97,248
Obligations of U.S. states and political subdivisions	1,734,529	2,152,253
Corporate debt securities	2,255,065	2,066,838
ABS	70,935	4,923
RMBS	154,963	181,849
CMBS	270,220	297,312
CLOs	307,607	101,023
Total fixed income securities	4,939,951	4,901,446
Equity securities	0	0
Total investments at fair value	4,939,951	4,901,446
Real estate acquired	0	0
Significant Unobservable Inputs (Level 3)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
U.S. Treasury securities and obligations of U.S. government corporations and agencies	0	0
Obligations of U.S. states and political subdivisions	77	271
Corporate debt securities	0	0
ABS	0	0
RMBS	0	0
CMBS	0	0
CLOs	0	0
Total fixed income securities	77	271
Equity securities	4,831	4,268
Total investments at fair value	4,908	4,539
Real estate acquired	$ 12,339	$ 12,713

Fair Value Measurements - Unobservable Input Reconciliation (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Total Investments
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance at beginning of period	$ 1,360	$ 4,845	$ 4,539	$ 4,959
Transfers out of Level 3			(3,100)
Total realized gains (losses):
Included in earnings and reported as net realized investment gains	3,663		3,663
Included in earnings and reported as losses incurred, net	0	0	0	0
Purchases	0	0	0	0
Sales	(115)	(197)	(194)	(311)
Balance at end of period	4,908	4,648	4,908	4,648
Debt Securities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance at beginning of period	192	577	271	691
Transfers out of Level 3			0
Total realized gains (losses):
Included in earnings and reported as net realized investment gains	0		0
Included in earnings and reported as losses incurred, net	0	0	0	0
Purchases	0	0	0	0
Sales	(115)	(197)	(194)	(311)
Balance at end of period	77	380	77	380
Equity securities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance at beginning of period	1,168	4,268	4,268	4,268
Transfers out of Level 3			(3,100)
Total realized gains (losses):
Included in earnings and reported as net realized investment gains	3,663		3,663
Included in earnings and reported as losses incurred, net	0	0	0	0
Purchases	0	0	0	0
Sales	0	0	0	0
Balance at end of period	4,831	4,268	4,831	4,268
Real Estate Acquired
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance at beginning of period	13,321	10,271	12,713	11,748
Transfers out of Level 3			0
Total realized gains (losses):
Included in earnings and reported as net realized investment gains	0		0
Included in earnings and reported as losses incurred, net	(450)	(592)	(1,104)	(818)
Purchases	7,979	8,881	24,742	26,985
Sales	(8,511)	(6,832)	(24,012)	(26,187)
Balance at end of period	$ 12,339	$ 11,728	$ 12,339	$ 11,728

Fair Value Measurements - Liabilities Not Measured at Fair Value (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Carrying Value
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
FHLB Advance	$ 155,000	$ 155,000
5.75% Senior Notes	419,425	418,560
9% Convertible Junior Subordinated Debentures	256,872	256,872
Total financial liabilities	831,297	830,432
Fair Value \| Significant Other Observable Inputs (Level 2)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
FHLB Advance	148,288	152,124
5.75% Senior Notes	445,430	465,473
9% Convertible Junior Subordinated Debentures	347,458	353,507
Total financial liabilities	$ 941,176	$ 971,104
Senior Notes \| 5.75% Senior Notes Due 2023
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Stated interest rate	5.75%
9% Convertible Junior Subordinated Debentures
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Stated interest rate	9.00%

Other Comprehensive Income (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Total other comprehensive (loss) income	$ (14,730)	$ 17,535	$ (107,759)	$ 75,387
Income tax benefit (expense)	3,093	(6,138)	22,629	(26,384)
Other comprehensive (loss) income, net of tax	(11,637)	11,397	(85,130)	49,003
Amounts Reclassified From Accumulated Other Comprehensive Income [Abstract]
Net realized investment gains (losses)	1,114	(50)	(1,112)	(227)
Other underwriting and operating expenses, net	(43,655)	(39,888)	(131,587)	(119,164)
Income before tax	231,894	184,467	649,441	539,040
Income tax benefit (expense)	(49,994)	(64,440)	(137,090)	(210,593)
Net income	181,900	120,027	512,351	328,447
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance, beginning of period			3,154,526
Other comprehensive income before reclassifications			(91,413)
Less: Amounts reclassified from AOCL			(6,283)
Balance, end of period	3,489,531	3,130,149	3,489,531	3,130,149
Reclassification from Accumulated Other Comprehensive Income
Amounts Reclassified From Accumulated Other Comprehensive Income [Abstract]
Income before tax	(3,125)	(201)	(7,953)	(1,886)
Income tax benefit (expense)	657	71	1,670	660
Net income	(2,468)	(130)	(6,283)	(1,226)
Accumulated other comprehensive (loss) income
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Other comprehensive (loss) income, net of tax			(85,130)	49,003
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance, beginning of period			(43,801)	(75,100)
Balance, end of period	(128,931)	(26,097)	(128,931)	(26,097)
Net unrealized gains and losses on available-for-sale securities
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Total other comprehensive (loss) income	(15,288)	17,761	(109,433)	76,022
Income tax benefit (expense)	3,211	(6,217)	22,981	(26,608)
Other comprehensive (loss) income, net of tax	(12,077)	11,544	(86,452)	49,414
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance, beginning of period			29,257
Other comprehensive income before reclassifications			(91,413)
Less: Amounts reclassified from AOCL			(4,961)
Balance, end of period	(57,195)		(57,195)
Net unrealized gains and losses on available-for-sale securities \| Reclassification from Accumulated Other Comprehensive Income
Amounts Reclassified From Accumulated Other Comprehensive Income [Abstract]
Net realized investment gains (losses)	(2,567)	(427)	(6,279)	(2,566)
Income tax benefit (expense)	539	150	1,318	898
Net income	(2,028)	(277)	(4,961)	(1,668)
Net benefit plan assets and obligations recognized in shareholders' equity
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Total other comprehensive (loss) income	558	(226)	1,674	(680)
Income tax benefit (expense)	(118)	79	(352)	238
Other comprehensive (loss) income, net of tax	440	(147)	1,322	(442)
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance, beginning of period			(73,058)
Other comprehensive income before reclassifications			0
Less: Amounts reclassified from AOCL			(1,322)
Balance, end of period	(71,736)		(71,736)
Net benefit plan assets and obligations recognized in shareholders' equity \| Reclassification from Accumulated Other Comprehensive Income
Amounts Reclassified From Accumulated Other Comprehensive Income [Abstract]
Other underwriting and operating expenses, net	(558)	226	(1,674)	680
Income tax benefit (expense)	118	(79)	352	(238)
Net income	(440)	147	(1,322)	442
Net unrealized foreign currency translation
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Total other comprehensive (loss) income	0	0	0	45
Income tax benefit (expense)	0	0	0	(14)
Other comprehensive (loss) income, net of tax	$ 0	$ 0	$ 0	$ 31

Benefit Plans (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
Benefit Plans (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Pension and Supplemental Executive Retirement Plans
Components of Net Periodic Benefit Cost [Abstract]
Service cost	$ 2,633	$ 2,389	$ 7,898	$ 7,167
Interest cost	3,774	3,869	11,321	11,606
Expected return on plan assets	(5,563)	(5,025)	(16,688)	(15,074)
Amortization of net actuarial losses/(gains)	1,734	1,543	5,203	4,627
Amortization of prior service cost/(credit)	(88)	(107)	(263)	(320)
Net periodic benefit cost (benefit)	2,490	2,669	7,471	8,006
Estimated future employer contributions in current fiscal year	11,000		11,000
Other Postretirement Benefit Plans
Components of Net Periodic Benefit Cost [Abstract]
Service cost	290	203	870	610
Interest cost	208	176	625	529
Expected return on plan assets	(1,590)	(1,312)	(4,769)	(3,936)
Amortization of net actuarial losses/(gains)	(62)	0	(187)	0
Amortization of prior service cost/(credit)	(1,026)	(1,662)	(3,078)	(4,987)
Net periodic benefit cost (benefit)	$ (2,180)	$ (2,595)	$ (6,539)	$ (7,784)

Income Taxes (Details) - USD ($)	3 Months Ended
Income Taxes (Details) - USD ($)	Sep. 30, 2018	Dec. 31, 2017
Income Tax Disclosure [Abstract]
Net operating loss carryforwards	$ 153,500,000
Valuation allowance	0	$ 0
Information regarding income tax examinations [Abstract]
Decrease in unrecognized tax benefits upon settlement of IRS dispute	144,900,000
Total amount of unrecognized tax benefits	$ 0

Loss Reserves - Reconciliation of Beginning and Ending Balances (Details) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017
Loss Reserve [Roll Forward]
Reserve at beginning of period	$ 985,635	$ 1,438,813
Less reinsurance recoverable	48,474	50,493
Net reserve at beginning of period	937,161	1,388,320
Losses and LAE incurred in respect of delinquency notices received in:
Current year	155,808	219,485
Prior years	(146,931)	(134,780)
Total losses incurred	8,877	84,705
Losses and LAE paid in respect of delinquency notices received in:
Current year	2,449	5,474
Prior years	257,808	407,977
Reinsurance terminations	(1,984)	301
Total losses paid	258,273	413,752
Net reserve at end of period	687,765	1,059,273
Plus reinsurance recoverables	33,281	45,878
Reserve at end of period	$ 721,046	$ 1,105,151

Loss Reserves (Details) $ in Thousands	3 Months Ended		9 Months Ended
Loss Reserves (Details) $ in Thousands	Sep. 30, 2018 USD ($) loan	Sep. 30, 2017 loan	Sep. 30, 2018 USD ($) loan	Sep. 30, 2017 USD ($) loan	Dec. 31, 2017 USD ($)
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Percentage of prior year delinquent inventory resolved (as a percent)			65.00%	59.00%
Prior years \| $			$ 257,808	$ 407,977
Premium refund liability, expected claim payments \| $	$ 44,000		44,000		$ 61,000
Prior years \| $			$ (146,931)	$ (134,780)
Primary Delinquent Inventory [Roll Forward]
Delinquent inventory at the beginning of period (in loans) \| loan	36,037	41,317	46,556	50,282
New notices (in loans) \| loan	13,569	15,950	40,351	45,352
Cures (in loans) \| loan	(14,197)	(13,546)	(47,620)	(45,382)
Paids (including those charged to a deductible or captive) (in loans) \| loan	(1,374)	(2,195)	(4,446)	(7,403)
Rescissions and denials (in loans) \| loan	(56)	(82)	(200)	(277)
Other items removed from inventory (in loans) \| loan	(581)	(209)	(1,243)	(1,337)
Delinquent inventory at end of period (in loans) \| loan	33,398	41,235	33,398	41,235
Settlements for commutations of coverage, pools of nonperforming loans, and claims paying practices
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Prior years \| $			$ 40,000	$ 54,000
Decrease in estimated claim rate on primary defaults
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Prior years \| $			(184,000)	(138,000)
Increase in estimated severity on primary defaults
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Prior years \| $			22,000	(2,000)
Change in estimates related to pool reserves, LAE reserves and reinsurance
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Prior years \| $			$ 15,000	$ 5,000

Loss Reserves - Delinquent Items (Details) - loan	Sep. 30, 2018	Jun. 30, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Dec. 31, 2016
Aging of the Primary Delinquent Inventory [Abstract]
3 months or less (in loans)	9,484		17,119	11,331
3 months or less (as a percent)	28.00%		37.00%	27.00%
4 - 11 months (in loans)	9,564		12,050	11,092
4 - 11 months (as a percent)	29.00%		26.00%	27.00%
12 months or more (in loans)	14,350		17,387	18,812
12 months or more (as a percent)	43.00%		37.00%	46.00%
Total primary delinquent inventory (in loans)	33,398	36,037	46,556	41,235	41,317	50,282
Total primary delinquent inventory (as a percent)	100.00%		100.00%	100.00%
Primary claims received inventory included in ending delinquent inventory (in loans)	766		954	1,063
Primary claims received inventory included in ending delinquent inventory (as a percent)	2.00%		2.00%	3.00%
Percent of 12 months or more delinquent inventory, delinquent for more than 36 months (as a percent)	39.00%		45.00%	45.00%
Number of payments delinquent [Abstract]
3 payments or less (in loans)	14,813		21,678	16,916
3 payments or less (as a percent)	44.00%		46.00%	41.00%
4 - 11 payments (in loans)	9,156		12,446	10,583
4 - 11 payments (as a percent)	28.00%		27.00%	26.00%
12 payments or more (in loans)	9,429		12,432	13,736
12 payments or more (as a percent)	28.00%		27.00%	33.00%
Total primary delinquent inventory (in loans)	33,398	36,037	46,556	41,235	41,317	50,282
Total primary delinquent inventory (as a percent)	100.00%		100.00%	100.00%
Percent of 12 payments or more delinquent inventory, 36 payments or more delinquent (as a percent)	39.00%		43.00%	43.00%
Pool insurance delinquent inventory (in loans)	1,032		1,309	1,426

Shareholders' Equity (Details) - USD ($)		3 Months Ended
Shareholders' Equity (Details) - USD ($)	Aug. 01, 2018	Jun. 30, 2018	Apr. 26, 2018
Class of Warrant or Right [Line Items]
Stock repurchase program, authorized amount			$ 200,000,000
Shares repurchased during period (in shares)		9,200,000
Shares repurchased, weighted average price per share		$ 10.88
Common stock, beneficial ownership threshold to be considered an Acquiring Person (as a percent)	5.00%
Common shares purchasable per Right (in shares)	0.1
Shareholder rights accompanying each outstanding share of the company's common stock (in number of Rights)	1
Purchase price (in dollars per share)	$ 45
Purchase price, one-tenth share (in dollars per share)	4.50
Redemption price (in dollars per Right)	$ 0.001
Rights
Class of Warrant or Right [Line Items]
Number of rights per outstanding share of common stock (in shares)	1
Period after public announcement that a person has become an acquirer (in days)	10 days
Period after a person announces a tender offer which would make them an acquirer (in days)	10 days

Share-Based Compensation (Details) - $ / shares shares in Thousands	9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017
RSUs subject to performance conditions
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Granted (in shares)	1,239	1,237
Weighted Average Share Fair Value (in dollars per share)	$ 15.80	$ 10.41
RSUs subject only to service conditions
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Granted (in shares)	447	395
Weighted Average Share Fair Value (in dollars per share)	$ 15.39	$ 10.41
Minimum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award vesting period (in years)	1 year
Maximum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award vesting period (in years)	3 years

Statutory Information (Details) $ in Millions	3 Months Ended	9 Months Ended	12 Months Ended
Statutory Information (Details) $ in Millions	Sep. 30, 2018 USD ($) jurisdiction	Sep. 30, 2018 USD ($) jurisdiction	Dec. 31, 2017 USD ($)
Statutory capital requirements [Abstract]
Number of jurisdictions with risk-to-capital requirements (in jurisdictions) \| jurisdiction	16	16
Maximum permitted risk-to-capital ratio commonly applied		25 to 1
Risk to capital ratio of combined insurance operations, including reinsurance affiliates, at end of period		9.8 to 1
Risk-to-capital ratio for combined insurance operations	9.8	9.8
Percentage of statutory policyholders surplus used to determine maximum allowable dividends (as a percent)	10.00%	10.00%
Mortgage Guaranty Insurance Corporation
Statutory capital requirements [Abstract]
Maximum risk-to-capital ratio		25
Risk to capital ratio at end of period		9.0 to 1
Risk-to-capital ratio	9.0	9.0
Amount of policyholders position above or below required MPP	$ 2,500	$ 2,500
Amount of required MPP	1,300	$ 1,300
Dividends paid to the parent company	$ 60
Adjusted statutory net income measurement period (in years)		3 years
Adjusted statutory net income dividend payment measurement period (in years)		2 years
Reduction in statutory net income due to increase in contingency reserve			$ 473
Statutory net income			$ 272

Subsequent Events Subsequent Events (Details) - Subsequent event	Oct. 30, 2018 USD ($)
Subsequent Event [Line Items]
Aggregate excess of loss reinsurance coverage	$ 318,600,000
Amortization period excess of loss reinsurance coverage	10 years
Mortgage Guaranty Insurance Corporation
Subsequent Event [Line Items]
Aggregate excess of loss reinsurance retained by company	$ 168,700,000
Excess of loss reinsurance coverage, option to terminate period	7 years
Home Re \| Mortgage insurance-linked notes
Subsequent Event [Line Items]
Debt instrument, face amount	$ 318,600,000.0
Term of mortgage insurance-linked notes	10 years