NMI (NMIH) 10-Q 3 Nov 21 2021 Q3 Quarterly report Financial data

COVER PAGE

COVER PAGE - shares	9 Months Ended
	Sep. 30, 2021	Oct. 29, 2021
Cover [Abstract]
Document Type	10-Q
Document Quarterly Report	true
Document Period End Date	Sep. 30, 2021
Document Transition Report	false
Entity File Number	001-36174
Entity Registrant Name	NMI Holdings, Inc.
Entity Incorporation, State or Country Code	DE
Entity Tax Identification Number	45-4914248
Entity Address, Address Line One	2100 Powell Street
Entity Address, City or Town	Emeryville
Entity Address, State or Province	CA
Entity Address, Postal Zip Code	94608
City Area Code	855
Local Phone Number	530-6642
Title of 12(b) Security	Class A Common Stock, par value $0.01
Trading Symbol	NMIH
Security Exchange Name	NASDAQ
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Large Accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
Entity Shell Company	false
Entity Common Stock, Shares Outstanding (in shares)		85,745,650
Entity Central Index Key	0001547903
Current Fiscal Year End Date	--12-31
Document Fiscal Year Focus	2021
Document Fiscal Period Focus	Q3
Amendment Flag	false

CONDENSED CONSOLIDATED BALANCE

CONDENSED CONSOLIDATED BALANCE SHEETS (UNAUDITED) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Assets
Fixed maturities, available-for-sale, at fair value (amortized cost of $2,024,639 and $1,730,835 as of September 30, 2021 and December 31, 2020, respectively)	$ 2,054,419	$ 1,804,286
Cash and cash equivalents (including restricted cash of $3,572 and $5,555 as of September 30, 2021 and December 31, 2020, respectively)	97,260	126,937
Premiums receivable	58,499	49,779
Accrued investment income	12,114	9,862
Prepaid expenses	4,409	3,292
Deferred policy acquisition costs, net	61,362	62,225
Software and equipment, net	32,066	29,665
Intangible assets and goodwill	3,634	3,634
Prepaid reinsurance premiums	2,969	6,190
Reinsurance recoverable	20,420	17,608
Other assets	51,162	53,188
Total assets	2,398,314	2,166,666
Liabilities
Debt	394,282	393,301
Unearned premiums	139,624	118,817
Accounts payable and accrued expenses	78,657	61,716
Reserve for insurance claims and claim expenses	104,604	90,567
Reinsurance funds withheld	6,280	8,653
Warrant liability, at fair value	3,010	4,409
Deferred tax liability, net	151,364	112,586
Other liabilities	4,267	7,026
Total liabilities	882,088	797,075
Commitments and contingencies
Shareholders' equity
Common Stock, Value, Outstanding	857	852
Additional paid-in capital	948,395	937,872
Accumulated other comprehensive income, net of tax	19,357	53,856
Retained earnings	547,617	377,011
Total shareholders' equity	1,516,226	1,369,591
Total liabilities and shareholders' equity	$ 2,398,314	$ 2,166,666

CONDENSED CONSOLIDATED BALANC_2

CONDENSED CONSOLIDATED BALANCE SHEETS (UNAUDITED) (Parenthetical) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Statement of Financial Position [Abstract]
Debt securities, amortized cost	$ 2,024,639	$ 1,730,835
Restricted cash	$ 3,572	$ 5,555
Common stock, par value (in dollars per share)	$ 0.01	$ 0.01
Common stock, issued (in shares)	85,743,638	85,163,039
Common stock, outstanding (in shares)	85,743,638	85,163,039
Common stock, authorized (in shares)	250,000,000	250,000,000

CONDENSED CONSOLIDATED STATEMEN

CONDENSED CONSOLIDATED STATEMENTS OF OPERATIONS AND COMPREHENSIVE INCOME (UNAUDITED) - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Revenues
Net premiums earned	$ 113,594	$ 98,802	$ 330,361	$ 296,463
Net investment income	9,831	8,337	28,027	23,511
Net realized investment gains (losses)	3	(4)	15	635
Other revenues	613	648	1,597	2,771
Total revenues	124,041	107,783	360,000	323,380
Expenses
Insurance claims and claim expenses	3,204	15,667	12,806	55,698
Underwriting and operating expenses	34,669	33,969	103,460	96,616
Service expenses	787	557	1,859	2,381
Interest expense	7,930	7,796	23,767	16,481
(Gain) loss from change in fair value of warrant liability	0	437	(454)	(4,286)
Total expenses	46,590	58,426	141,438	166,890
Income before income taxes	77,451	49,357	218,562	156,490
Income tax expense	17,258	11,178	47,956	33,192
Net income	$ 60,193	$ 38,179	$ 170,606	$ 123,298
Earnings per share
Basic (in dollars per share)	$ 0.70	$ 0.45	$ 1.99	$ 1.63
Diluted (in dollars per share)	$ 0.69	$ 0.45	$ 1.96	$ 1.55
Weighted average common shares outstanding
Basic (in shares)	85,721	84,805	85,563	75,695
Diluted (in shares)	86,880	85,599	86,794	76,867
Comprehensive income:
Net income	$ 60,193	$ 38,179	$ 170,606	$ 123,298
Other comprehensive income (loss), net of tax:
Unrealized (losses) gains in accumulated other comprehensive gain (loss), net of tax (benefit) expense of $(2,165) and $2,494 for the three months ended September 30, 2021 and 2020, and $(9,168) and $7,655 for the nine months ended September 30, 2021 and 2020, respectively	(8,144)	9,381	(34,487)	28,799
Reclassification adjustment for realized (gains) losses included in net income, net of tax expense (benefit) of $1 and $(1) for the three months ended September 30, 2021 and 2020, and $3 and $(258) for the nine months ended September 30, 2021 and 2020, respectively	(2)	3	(12)	972
Other comprehensive income (loss), net of tax	(8,146)	9,384	(34,499)	29,771
Comprehensive income	$ 52,047	$ 47,563	$ 136,107	$ 153,069

CONDENSED CONSOLIDATED STATEM_2

CONDENSED CONSOLIDATED STATEMENTS OF OPERATIONS AND COMPREHENSIVE INCOME (UNAUDITED) (Parenthetical) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Income Statement [Abstract]
Net unrealized (losses) gains in accumulated other comprehensive income, tax (benefit) expense	$ (2,165)	$ 2,494	$ (9,168)	$ 7,655
Reclassification adjustment for realized losses (gains) included in net income, tax expense (benefit)	$ 1	$ (1)	$ 3	$ (258)

CONDENSED CONSOLIDATED STATEM_3

CONDENSED CONSOLIDATED STATEMENTS OF CHANGES IN SHAREHOLDERS' EQUITY (UNAUDITED) - USD ($) $ in Thousands		Total	Common Stock - Class A		Additional Paid-in Capital	Accumulated Other Comprehensive Income	Retained Earnings
Beginning balance (in shares) at Dec. 31, 2019			68,358,000
Beginning balance at Dec. 31, 2019		$ 930,420	$ 684		$ 707,003	$ 17,288	$ 205,445
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Common stock: class A shares issued related to warrant exercises (in shares)	[1]		6,474
Common stock: class A shares issued related to warrant exercises		221			221
Common stock: class A shares issued under stock plans, net of shares withheld for employee taxes (in shares)			510,000
Common stock: class A shares issued under stock plans, net of shares withheld for employee taxes		(3,750)	$ 5		(3,755)
Share-based compensation expense		2,552			2,552
Change in unrealized investment gains/losses, net of tax benefit/expense		(12,824)				(12,824)
Net income		58,271					58,271
Ending balance (in shares) at Mar. 31, 2020			68,874,000
Ending balance at Mar. 31, 2020		974,890	$ 689		706,021	4,464	263,716
Beginning balance (in shares) at Dec. 31, 2019			68,358,000
Beginning balance at Dec. 31, 2019		$ 930,420	$ 684		707,003	17,288	205,445
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Common stock: class A shares issued related to warrant exercises (in shares)		6,000
Net income		$ 123,298
Ending balance (in shares) at Sep. 30, 2020			84,809,000
Ending balance at Sep. 30, 2020		1,307,556	$ 848		930,906	47,059	328,743
Beginning balance (in shares) at Mar. 31, 2020			68,874,000
Beginning balance at Mar. 31, 2020		974,890	$ 689		706,021	4,464	263,716
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Common stock: class A shares issued related to public offering (in shares)			15,870,000
Common stock: class A shares issued related to public offering		219,687	$ 159		219,528
Common stock: class A shares issued under stock plans, net of shares withheld for employee taxes (in shares)	[1]		61,226
Common stock: class A shares issued under stock plans, net of shares withheld for employee taxes		(321)			(321)
Share-based compensation expense		2,722			2,722
Change in unrealized investment gains/losses, net of tax benefit/expense		33,211				33,211
Net income		26,848					26,848
Ending balance (in shares) at Jun. 30, 2020			84,805,000
Ending balance at Jun. 30, 2020		1,257,037	$ 848		927,950	37,675	290,564
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Common stock: class A shares issued under stock plans, net of shares withheld for employee taxes (in shares)	[1]		3,750
Common stock: class A shares issued under stock plans, net of shares withheld for employee taxes		0
Share-based compensation expense		2,956			2,956
Change in unrealized investment gains/losses, net of tax benefit/expense		9,384				9,384
Net income		38,179					38,179
Ending balance (in shares) at Sep. 30, 2020			84,809,000
Ending balance at Sep. 30, 2020		1,307,556	$ 848		930,906	47,059	328,743
Beginning balance (in shares) at Dec. 31, 2020			85,163,000
Beginning balance at Dec. 31, 2020		1,369,591	$ 852		937,872	53,856	377,011
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Common stock: class A shares issued related to warrant exercises (in shares)	[2]		23,750
Common stock: class A shares issued related to warrant exercises		557			557
Common stock: class A shares issued under stock plans, net of shares withheld for employee taxes (in shares)			413,000
Common stock: class A shares issued under stock plans, net of shares withheld for employee taxes		(620)	$ 4		(624)
Share-based compensation expense		3,022			3,022
Change in unrealized investment gains/losses, net of tax benefit/expense		(45,133)				(45,133)
Net income		52,891					52,891
Ending balance (in shares) at Mar. 31, 2021			85,600,000
Ending balance at Mar. 31, 2021		1,380,308	$ 856		940,827	8,723	429,902
Beginning balance (in shares) at Dec. 31, 2020			85,163,000
Beginning balance at Dec. 31, 2020		$ 1,369,591	$ 852		937,872	53,856	377,011
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Common stock: class A shares issued related to warrant exercises (in shares)		60,000
Common stock: class A shares issued under stock plans, net of shares withheld for employee taxes (in shares)			12,436
Net income		$ 170,606
Ending balance (in shares) at Sep. 30, 2021			85,743,000
Ending balance at Sep. 30, 2021		1,516,226	$ 857		948,395	19,357	547,617
Beginning balance (in shares) at Mar. 31, 2021			85,600,000
Beginning balance at Mar. 31, 2021		1,380,308	$ 856		940,827	8,723	429,902
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Common stock: class A shares issued related to warrant exercises (in shares)	[2]		8,096
Common stock: class A shares issued related to warrant exercises		197			197
Common stock: class A shares issued under stock plans, net of shares withheld for employee taxes (in shares)			95,000
Common stock: class A shares issued under stock plans, net of shares withheld for employee taxes		(285)	$ 1		(286)
Share-based compensation expense		3,383			3,383
Change in unrealized investment gains/losses, net of tax benefit/expense		18,780				18,780
Net income		57,522					57,522
Ending balance (in shares) at Jun. 30, 2021			85,703,000
Ending balance at Jun. 30, 2021		$ 1,459,905	$ 857		944,121	27,503	487,424
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Common stock: class A shares issued related to warrant exercises (in shares)		28,000	27,715	[2]
Common stock: class A shares issued related to warrant exercises		$ 603			603
Common stock: class A shares issued under stock plans, net of shares withheld for employee taxes (in shares)	[2]		12,000
Common stock: class A shares issued under stock plans, net of shares withheld for employee taxes		(45)			(45)
Share-based compensation expense		3,716			3,716
Change in unrealized investment gains/losses, net of tax benefit/expense		(8,146)				(8,146)
Net income		60,193					60,193
Ending balance (in shares) at Sep. 30, 2021			85,743,000
Ending balance at Sep. 30, 2021		$ 1,516,226	$ 857		$ 948,395	$ 19,357	$ 547,617
[1]	During the three months ended March 31, 2020, we issued 6,474 common shares with a par value of $0.01 in connection with the exercise of warrants, which is not identifiable in this schedule due to rounding. During the three months ended June 30, 2020 and September 30, 2020, we issued 61,226 and 3,750 common shares, respectively, with a par value of $0.01 in connection with the exercise of options and vesting of restricted stock units granted under our stock plans, which are not identifiable in this schedule due to rounding.
[2]	During the three months ended March 31, 2021 and June 30, 2021, we issued 23,750 and 8,096 common shares, respectively, with a par value of $0.01 in connection with the exercise of warrants, which are not identifiable in this schedule due to rounding. During the three months ended September 30, 2021, we issued 27,715 common shares with a par value of $0.01 in connection with the exercise of warrants, and 12,436 common shares with a par value of $0.01 in connection with the exercise of options and vesting of restricted stock units granted under our stock plans, which are not identifiable in this schedule due to rounding.

CONDENSED CONSOLIDATED STATEM_4

CONDENSED CONSOLIDATED STATEMENTS OF CHANGES IN SHAREHOLDERS' EQUITY (UNAUDITED) (Parenthetical) - USD ($) $ in Thousands	3 Months Ended
	Sep. 30, 2021		Jun. 30, 2021		Mar. 31, 2021		Sep. 30, 2020		Jun. 30, 2020		Mar. 31, 2020
Change in unrealized investment gains/losses, tax expense (benefit)	$ (2,166)		$ 4,992		$ (11,997)		$ 2,494		$ 8,829		$ (3,409)
Common stock: class A shares issued related to warrant exercises (in shares)	28,000
Common stock, par value (in dollars per share)	$ 0.01
Common stock
Common stock: class A shares issued related to warrant exercises (in shares)	27,715	[1]	8,096	[1]	23,750	[1]					6,474	[2]
Common stock, par value (in dollars per share)	$ 0.01		$ 0.01		$ 0.01		$ 0.01				$ 0.01
Common stock: class A shares issued under stock plans, net of shares withheld for employee taxes (in shares)	12,000	[1]	95,000		413,000		3,750	[2]	61,226	[2]	510,000
[1]	During the three months ended March 31, 2021 and June 30, 2021, we issued 23,750 and 8,096 common shares, respectively, with a par value of $0.01 in connection with the exercise of warrants, which are not identifiable in this schedule due to rounding. During the three months ended September 30, 2021, we issued 27,715 common shares with a par value of $0.01 in connection with the exercise of warrants, and 12,436 common shares with a par value of $0.01 in connection with the exercise of options and vesting of restricted stock units granted under our stock plans, which are not identifiable in this schedule due to rounding.
[2]	During the three months ended March 31, 2020, we issued 6,474 common shares with a par value of $0.01 in connection with the exercise of warrants, which is not identifiable in this schedule due to rounding. During the three months ended June 30, 2020 and September 30, 2020, we issued 61,226 and 3,750 common shares, respectively, with a par value of $0.01 in connection with the exercise of options and vesting of restricted stock units granted under our stock plans, which are not identifiable in this schedule due to rounding.

CONDENSED CONSOLIDATED STATEM_5

CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS (UNAUDITED) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020
Cash flows from operating activities
Net income	$ 170,606	$ 123,298
Adjustments to reconcile net income to net cash provided by operating activities:
Net realized investment gains	(15)	(635)
Gain from change in fair value of warrant liability	(454)	(4,286)
Depreciation and amortization	8,250	7,378
Net amortization of premium on investment securities	5,020	2,116
Amortization of debt discount and debt issuance costs	1,349	3,600
Deferred income taxes	47,949	33,178
Share-based compensation expense	10,121	8,230
Changes in operating assets and liabilities:
Premiums receivable	(8,720)	(2,074)
Accrued investment income	(2,252)	(2,935)
Prepaid expenses	(1,117)	(1,067)
Deferred policy acquisition costs, net	863	(3,222)
Other assets	(79)	(81)
Unearned premiums	20,807	(20,634)
Reserve for insurance claims and claim expenses	14,037	63,478
Reinsurance recoverable	(2,812)	(12,241)
Reinsurance balances, net	(174)	2,857
Accounts payable and accrued expenses	18,002	18,017
Net cash provided by operating activities	281,381	214,977
Cash flows from investing activities
Purchase of short-term investments	(10,640)	(41,872)
Purchase of fixed-maturity investments, available-for-sale	(390,988)	(902,524)
Proceeds from maturity of short-term investments	0	85,689
Proceeds from redemptions, maturities and sale of fixed-maturity investments, available-for-sale	100,215	346,931
Software and equipment	(9,107)	(9,102)
Net cash used in investing activities	(310,520)	(520,878)
Cash flows from financing activities
Proceeds from issuance of common stock related to public offering, net of issuance costs	0	219,687
Proceeds from issuance of common stock related to employee equity plans	4,137	3,407
Proceeds from issuance of common stock related to warrants	412	0
Taxes paid related to net share settlement of equity awards	(5,087)	(7,465)
Proceeds from senior secured notes	0	400,000
Repayments of term loan	0	(147,750)
Payments of debt issuance/modification costs	0	(8,868)
Net cash (used in) provided by financing activities	(538)	459,011
Net (decrease) increase in cash, cash equivalents and restricted cash	(29,677)	153,110
Cash, cash equivalents and restricted cash, beginning of period	126,937	41,089
Cash, cash equivalents and restricted cash, end of period	97,260	194,199
Supplemental disclosures of cash flow information
Interest paid	14,750	4,286
Income taxes refunded	$ 457	$ 76

Organization, Basis of Presenta

Organization, Basis of Presentation and Summary of Accounting Principles	9 Months Ended
	Sep. 30, 2021
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Organization, Basis of Presentation and Summary of Accounting Principles	Organization, Basis of Presentation and Summary of Accounting Principles NMI Holdings, Inc. (NMIH) is a Delaware corporation, incorporated in May 2011, to provide private mortgage guaranty insurance (which we refer to as mortgage insurance or MI) through its wholly-owned insurance subsidiaries, National Mortgage Insurance Corporation (NMIC) and National Mortgage Reinsurance Inc One (Re One). Our common stock is listed on the NASDAQ exchange under the ticker symbol "NMIH." NMIC, our primary insurance subsidiary, issued its first mortgage insurance policy in April 2013. NMIC is licensed to write mortgage insurance in all 50 states and DC. In August 2015, NMIH capitalized a wholly-owned subsidiary, NMI Services, Inc. (NMIS), through which we offer outsourced loan review services to mortgage loan originators. Basis of Presentation The accompanying unaudited condensed consolidated financial statements, which include the results of NMIH and its wholly-owned subsidiaries, have been prepared in accordance with the instructions to Form 10-Q as prescribed by the SEC for interim reporting and include other information and disclosures required by accounting principles generally accepted in the U.S. (GAAP). Our accounts are maintained in U.S. dollars. These statements should be read in conjunction with our consolidated financial statements and notes thereto for the year ended December 31, 2020, included in our 2020 10-K. All intercompany transactions have been eliminated. The preparation of financial statements in accordance with GAAP requires management to make estimates and assumptions that affect reported amounts of assets and liabilities, as well as disclosure of contingent assets and liabilities as of the balance sheet date. Estimates also affect the reported amounts of income and expenses for the reporting period. Actual results could differ from those estimates. The results of operations for the interim period may not be indicative of the results that may be expected for the full year ending December 31, 2021. COVID-19 Developments On January 30, 2020, the World Health Organization (WHO) declared the outbreak of COVID-19 a global health emergency and subsequently characterized the outbreak as a global pandemic on March 11, 2020. In an effort to stem contagion and control the COVID-19 pandemic, the population at large severely curtailed day-to-day activity and local, state and federal regulators imposed a broad set of restrictions on personal and business conduct nationwide. The COVID-19 pandemic, along with the widespread public and regulatory response, caused a dramatic slowdown in U.S. and global economic activity and a record number of Americans were furloughed or laid-off in the ensuing downturn. The global dislocation caused by COVID-19 was unprecedented. In response to the COVID-19 outbreak and uncertainty that it introduced, we activated our disaster continuity program to ensure our employees were safe and able to manage our business without interruption. We pursued a broad series of capital and reinsurance transactions to bolster our balance sheet and expand our ability to serve our customers and their borrowers, and we updated our underwriting guidelines and policy pricing in consideration of the increased level of macroeconomic volatility. While there is increased optimism that the acute economic impact of COVID-19 has begun to recede, the pandemic continues to affect communities across the U.S. and poses significant risk globally. The path and pace of global economic recovery will depend, in large part, on the course of the virus, which itself remains unknown and subject to risk. Given this uncertainty, we are not able to fully assess or estimate the ultimate impact COVID-19 will have on the mortgage insurance market, our business performance or our financial position including our new business production, default and claims experience, and investment portfolio results at this time. Significant Accounting Principles There have been no changes to our significant accounting principles as described in Item 8, " Financial Statements and Supplementary Data - Notes to Consolidated Financial Statements - Note 2 - Summary of Accounting Principles " of our 2020 10-K, except as noted in " Variable Interest Entities " and " Recent Accounting Pronouncements - Adopted " below. Variable Interest Entities NMIC is a party to reinsurance agreements with Oaktown Re Ltd., Oaktown Re II Ltd., Oaktown Re III Ltd., Oaktown Re IV Ltd. Oaktown Re V Ltd., and Oaktown Re VI Ltd. (special purpose reinsurance entities collectively referred to as the Oaktown Re Vehicles) effective May 2, 2017, July 25, 2018, July 30, 2019, July 30, 2020, October 29, 2020 and April 27, 2021, respectively. At inception of the respective reinsurance agreements, we determined that each of the Oaktown Re Vehicles were variable interest entities (VIEs), as defined under GAAP Accounting Standards Codification (ASC) 810, because they did not have sufficient equity at risk to finance their respective activities. We evaluated the VIEs at inception to determine whether NMIC was the primary beneficiary under each reinsurance transaction and, if so, whether we were required to consolidate the assets and liabilities of each VIE. The primary beneficiary of a VIE is an enterprise that (1) has the power to direct the activities of the VIE, which most significantly impact its economic performance and (2) has significant economic exposure to the VIE, i.e. , the obligation to absorb losses or receive benefits that could potentially be significant. The determination of whether an entity is the primary beneficiary of a VIE is complex and requires management judgment regarding determinative factors, including the expected results of the VIE and how those results are absorbed by beneficial interest holders, as well as which party has the power to direct activities that most significantly impact the performance of the VIE. We concluded that we are not the primary beneficiary of each VIE and, as such, we do not consolidate them in our consolidated financial statements. Recent Accounting Pronouncements - Adopted In December 2019, the Financial Accounting Standards Board (the FASB) issued ASU 2019-12, Simplifying the Accounting for Income Taxes (Topic 740). The update eliminates certain exceptions for recognizing deferred taxes for investments, performing intra-period allocations and calculating income taxes in interim periods. The ASU also includes guidance to reduce complexity in certain income tax areas, including recognizing deferred taxes for tax goodwill and allocating taxes to members of a consolidated group. We adopted this ASU on January 1, 2021 and determined it did not have a material impact on our consolidated financial statements. Recent Accounting Pronouncements - Not Yet Adopted In August 2018, the FASB issued ASU 2018-12, Targeted Improvements to the Accounting for Long-Duration Contracts (Topic 944). The update provides guidance to the existing recognition, measurement, presentation and disclosure requirements for long-duration contracts issued by an insurance entity. The FASB subsequently issued ASU 2019-09 in November 2019 and ASU 2020-11 in November 2020, which amended the effective date for this standard and provided transition relief to facilitate early application for long duration contracts. These standards will now take effect for public business entities for fiscal years, and interim periods within those fiscal years, beginning after December 15, 2022. We are currently evaluating the impact the adoption of these ASUs will have, if any, on our consolidated financial statements. In March 2020, the FASB issued ASU 2020-04, Reference Rate Reform (Topic 848). The update provides optional guidance to ease the potential burden in accounting for reference rate reform on financial reporting. Reference rate reform refers to the global transition away from referencing the London Interbank Offered Rate (LIBOR) in financial contracts, which is expected to be discontinued beginning in 2021 through 2023. The ASU includes optional expedients and exceptions for applying GAAP to contracts, hedging relationships and other transactions affected by reference rate reform if certain criteria are met. This standard may be elected and applied prospectively over time from March 12, 2020 through December 31, 2022 as reference rate reform activities occur. The adoption of, and future elections under, this ASU are not expected to have a material impact on our consolidated financial statements as the ASU will ease, if warranted, the requirements for accounting for the future effects of the rate reform. We continue to monitor the impact the discontinuance of LIBOR or another reference rate will have on our contracts and other transactions. In August 2020, the FASB issued ASU 2020-06, Debt—Debt with Conversion and Other Options (Subtopic 470-20) and Derivatives and Hedging— Contracts in Entity's Own Equity (Subtopic 815-40 ). This update simplifies the accounting for convertible instruments and contracts on an entity's own equity, including warrants, eliminating certain triggers for derivative accounting. The standard will take effect for public business entities for fiscal years, and interim periods within those fiscal years, beginning after December 15, 2021. We have evaluated the impact the adoption of this ASU and we do not expect it to have a material impact on our consolidated financial statements, including our warrant liability.

Investments

Investments	9 Months Ended
	Sep. 30, 2021
Investments, Debt and Equity Securities [Abstract]
Investments	InvestmentsWe hold all investments on an available-for-sale basis and evaluate each position quarterly for impairment. We recognize an impairment on a security through the statement of operations if (i) we intend to sell the impaired security; or (ii) it is more likely than not that we will be required to sell the impaired security prior to recovery of its amortized cost basis. If a sale is intended or likely to be required, we write down the amortized cost basis of the security to fair value and recognize the full amount of the impairment through the statement of operations as a "Net Realized Investment Loss." To the extent we determine that a security impairment is credit-related, an impairment loss is recognized through the statement of operations as a provision for credit loss expense. The portion of a security impairment attributed to other non-credit related factors is recognized in other comprehensive income, net of taxes. Fair Values and Gross Unrealized Gains and Losses on Investments Amortized Gross Unrealized Fair Gains Losses As of September 30, 2021 (In Thousands) U.S. Treasury securities and obligations of U.S. government agencies $ 29,435 $ 1,384 $ — $ 30,819 Municipal debt securities 503,615 8,114 (2,735) 508,994 Corporate debt securities 1,375,589 32,051 (10,478) 1,397,162 Asset-backed securities 104,990 1,516 (77) 106,429 Total bonds 2,013,629 43,065 (13,290) 2,043,404 Short-term investments 11,010 5 — 11,015 Total investments $ 2,024,639 $ 43,070 $ (13,290) $ 2,054,419 Amortized Gross Unrealized Fair Gains Losses As of December 31, 2020 (In Thousands) U.S. Treasury securities and obligations of U.S. government agencies $ 29,412 $ 2,186 $ — $ 31,598 Municipal debt securities 407,323 14,027 (2) 421,348 Corporate debt securities 1,165,260 55,014 (483) 1,219,791 Asset-backed securities 128,471 2,736 (27) 131,180 Total bonds 1,730,466 73,963 (512) 1,803,917 Short-term investments 369 — — 369 Total investments $ 1,730,835 $ 73,963 $ (512) $ 1,804,286 We did not own any mortgage-backed securities i n our asset-backed securities portfolio at September 30, 2021 o r December 31, 2020. The following table presents a breakdown of the fair value of our corporate debt securities by issuer industry group as of September 30, 2021 and December 31, 2020: September 30, 2021 December 31, 2020 Financial 38 % 37 % Consumer 23 23 Communications 12 10 Technology 10 10 Utilities 10 11 Industrial 7 9 Total 100 % 100 % As of September 30, 2021 and December 31, 2020, approximately $5.6 million and $5.7 million, respectively, of our cash and investments were held in the form of U.S. Treasury securities on deposit with various state insurance departments to satisfy regulatory requirements. Scheduled Maturities The amortized cost and fair value of available-for-sale securities as of September 30, 2021 and December 31, 2020, by contractual maturity, are shown below. Expected maturities will differ from contractual maturities because issuers may have the right to call or prepay obligations with or without call or prepayment penalties. Because most asset-backed securities provide for periodic payments throughout their lives, they are listed below in a separate category. As of September 30, 2021 Amortized Fair (In Thousands) Due in one year or less $ 66,077 $ 66,624 Due after one through five years 624,658 646,757 Due after five through ten years 1,165,336 1,170,933 Due after ten years 63,578 63,676 Asset-backed securities 104,990 106,429 Total investments $ 2,024,639 $ 2,054,419 As of December 31, 2020 Amortized Fair (In Thousands) Due in one year or less $ 57,429 $ 57,949 Due after one through five years 507,444 536,520 Due after five through ten years 1,016,230 1,056,098 Due after ten years 21,261 22,539 Asset-backed securities 128,471 131,180 Total investments $ 1,730,835 $ 1,804,286 Aging of Unrealized Losses As of September 30, 2021, the investment portfolio had gross unrealized losses of $13.3 million, of which $1.3 million had been in an unrealized loss position for a period of twelve months or longer. As of December 31, 2020, the investment portfolio had gross unrealized losses of $512 thousand, of which $8 thousand had been in an unrealized loss position for a period of twelve months or longer. For those securities in an unrealized loss position, the length of time the securities were in such a position is as follows: Less Than 12 Months 12 Months or Greater Total # of Securities Fair Value Unrealized Losses # of Securities Fair Value Unrealized Losses # of Securities Fair Value Unrealized Losses As of September 30, 2021 (Dollars in Thousands) Municipal debt securities 116 $ 223,105 $ (2,735) — $ — 116 $ 223,105 $ (2,735) Corporate debt securities 94 598,002 (9,258) 4 29,367 (1,220) 98 627,369 (10,478) Asset-backed securities 2 4,228 (28) 1 2,001 (49) 3 6,229 (77) Short-term investments 2 1,649 — — — — 2 1,649 — Total 214 $ 826,984 $ (12,021) 5 $ 31,368 $ (1,269) 219 $ 858,352 $ (13,290) Less Than 12 Months 12 Months or Greater Total # of Securities Fair Value Unrealized Losses # of Securities Fair Value Unrealized Losses # of Securities Fair Value Unrealized Losses As of December 31, 2020 (Dollars in Thousands) Municipal debt securities 4 3,548 (2) — — — 4 3,548 (2) Corporate debt securities 9 40,081 (483) 1 33 — 10 40,114 (483) Asset-backed securities 2 5,191 (19) 1 2,495 (8) 3 7,686 (27) Total 15 $ 48,820 $ (504) 2 $ 2,528 $ (8) 17 $ 51,348 $ (512) Allowance for credit losses As of September 30, 2021 and December 31, 2020, we did not recognize an allowance for credit loss for any security in the investment portfolio and we did not record any provision for credit loss for investment securities during the three or nine month periods ended September 30, 2021 or September 30, 2020. The increase in the number of securities in and the aggregate size of the unrealized loss position as of September 30, 2021, was primarily driven by interest rate movements following the purchase date of certain securities. Based on current facts and circumstances, we believe the unrealized losses as of September 30, 2021 are not indicative of the ultimate collectability of the current amortized cost of the securities. Net Investment Income The following table presents the components of net investment income: For the three months ended September 30, For the nine months ended September 30, 2021 2020 2021 2020 (In Thousands) Investment income $ 10,170 $ 8,624 $ 29,003 $ 24,293 Investment expenses (339) (287) (976) (782) Net investment income $ 9,831 $ 8,337 $ 28,027 $ 23,511 The following table presents the components of net realized investment losses: For the three months ended September 30, For the nine months ended September 30, 2021 2020 2021 2020 (In Thousands) Gross realized investment gains $ 3 $ — $ 15 $ 5,126 Gross realized investment losses — (4) — (4,491) Net realized investment gains (losses) $ 3 $ (4) $ 15 $ 635

Fair Value of Financial Instrum

Fair Value of Financial Instruments	9 Months Ended
	Sep. 30, 2021
Fair Value Disclosures [Abstract]
Fair Value of Financial Instruments	Fair Value of Financial Instruments The following describes the valuation techniques used by us to determine the fair value of our financial instruments: We established a fair value hierarchy by prioritizing the inputs to valuation techniques used to measure fair value. The hierarchy gives the highest priority to unadjusted quoted prices in active markets for identical assets or liabilities (Level 1 measurements) and the lowest priority to unobservable inputs (Level 3 measurements). The three levels of the fair value hierarchy under this standard are described below: Level 1 - Fair value measurements based on quoted prices in active markets that we have the ability to access for identical assets or liabilities. Market price data generally is obtained from exchange or dealer markets. We do not adjust the quoted price for such instruments. Level 2 - Fair value measurements based on inputs other than quoted prices included in Level 1 that are observable for the asset or liability, either directly or indirectly. Level 2 inputs include quoted prices for similar assets and liabilities in active markets, quoted prices for identical or similar assets or liabilities in markets that are not active, and inputs other than quoted prices that are observable for the asset or liability, such as interest rates and yield curves that are observable at commonly quoted intervals. Level 3 - Fair value measurements based on valuation techniques that use significant inputs that are unobservable. Both observable and unobservable inputs may be used to determine the fair values of positions classified in Level 3. The circumstances for using these measurements include those in which there is little, if any, market activity for the asset or liability. Therefore, we must make certain assumptions, which require significant management judgment or estimation about the inputs a hypothetical market participant would use to value that asset or liability. In certain cases, the inputs used to measure fair value may fall into different levels of the fair value hierarchy. In such cases, the level in the fair value hierarchy is determined based on the lowest level input that is significant to the fair value measurement in its entirety. Assets classified as Level 1 and Level 2 To determine the fair value of securities available-for-sale in Level 1 and Level 2 of the fair value hierarchy, independent pricing sources have been utilized. One price is provided per security based on observable market data. To ensure securities are appropriately classified in the fair value hierarchy, we review the pricing techniques and methodologies of the independent pricing sources and believe that their policies adequately consider market activity, either based on specific transactions for the issue valued or based on modeling of securities with similar credit quality, duration, yield and structure that were recently traded. A variety of inputs are utilized by the independent pricing sources including benchmark yields, reported trades, non-binding broker/dealer quotes, issuer spreads, two sided markets, benchmark securities, bids, offers and reference data including data published in market research publications. Inputs may be weighted differently for any security, and not all inputs are used for each security evaluation. Market indicators, industry and economic events are also considered. This information is evaluated using a multidimensional pricing model. Quality controls are performed by the independent pricing sources throughout this process, which include reviewing tolerance reports, trading information and data changes, and directional moves compared to market moves. This model combines all inputs to arrive at a value assigned to each security. We have not made any adjustments to the prices obtained from the independent pricing sources. Liabilities classified as Level 3 We calculate the fair value of outstanding warrants utilizing Level 3 inputs, including a Black-Scholes option-pricing model, in combination with a binomial model, and we value the pricing protection features within the warrants using a Monte-Carlo simulation model. Variables in the model include the risk-free rate of return, dividend yield, expected life and expected volatility of our stock price. The following tables present the level within the fair value hierarchy at which our financial instruments were measured: Fair Value Measurements Using Quoted Prices in Significant Other Significant Fair Value As of September 30, 2021 (In Thousands) U.S. Treasury securities and obligations of U.S. government agencies $ 30,819 $ — $ — $ 30,819 Municipal debt securities — 508,994 — 508,994 Corporate debt securities — 1,397,162 — 1,397,162 Asset-backed securities — 106,429 — 106,429 Cash, cash equivalents and short-term investments 108,275 — — 108,275 Total assets $ 139,094 $ 2,012,585 $ — $ 2,151,679 Warrant liability — — 3,010 3,010 Total liabilities $ — $ — $ 3,010 $ 3,010 Fair Value Measurements Using Quoted Prices in Significant Other Significant Fair Value As of December 31, 2020 (In Thousands) U.S. Treasury securities and obligations of U.S. government agencies $ 31,598 $ — $ — $ 31,598 Municipal debt securities — 421,348 — 421,348 Corporate debt securities — 1,219,791 — 1,219,791 Asset-backed securities — 131,180 — 131,180 Cash, cash equivalents and short-term investments 127,306 — — 127,306 Total assets $ 158,904 $ 1,772,319 $ — $ 1,931,223 Warrant liability — — 4,409 4,409 Total liabilities $ — $ — $ 4,409 $ 4,409 There were no transfers between Level 2 and Level 3 of the fair value hierarchy during the nine months ended September 30, 2021, or the year ended December 31, 2020. The following table provides a roll-forward of Level 3 liabilities measured at fair value: For the nine months ended September 30, Warrant Liability 2021 2020 (In Thousands) Balance, January 1 $ 4,409 $ 7,641 Change in fair value of warrant liability included in earnings (454) (4,286) Issuance of common stock on warrant exercise (945) (220) Balance, September 30 $ 3,010 $ 3,135 The following table outlines the key inputs and assumptions used to calculate the fair value of the warrant liability in the Black-Scholes option-pricing model as of the dates indicated. As of September 30, 2021 2020 Common stock price $ 22.61 $ 17.80 Risk free interest rate 0.05 % 0.13 % Expected life 0.56 years 1.56 years Expected volatility 34.4 % 75.3 % Dividend yield 0 % 0 % The changes in fair value of the warrant liability for the nine months ended September 30, 2021 and 2020 were driven by the exercise of outstanding warrants, as well as changes in the price of our common stock and other Black-Scholes model inputs during the respective periods. Financial Instruments not Measured at Fair Value On June 19, 2020, we issued $400.0 million aggregate principal amount of senior secured notes that mature on June 1, 2025 (the Notes) and used a portion of the proceeds from the Notes offering to repay the outstanding amount due under our $150 million term loan (2018 Term Loan). At September 30, 2021, the Notes were carried at a cost of $394.3 million, net of unamortized debt issuance costs of $5.7 million, and had a fair value of $457.0 million as assessed under our Level 2 hierarchy. At December 31, 2020, the Notes were carried at a cost of $393.3 million, net of unamortized debt issuance costs of $6.7 million, and had a fair value of $447.1 million.

Debt

Debt	9 Months Ended
	Sep. 30, 2021
Debt Disclosure [Abstract]
Debt	Debt Senior Secured Notes At September 30, 2021, we had $400.0 million aggregate principal amount of senior secured notes outstanding. The Notes were issued pursuant to an indenture dated June 19, 2020 (the Indenture) and bear interest at a rate of 7.375%, payable semi-annually on June 1 and December 1. $244.4 million of proceeds from the Notes offering were contributed to our lead operating subsidiary, NMIC and remaining proceeds were used to repay the outstanding amount due under the 2018 Term Loan due on May 24, 2023 and to pay underwriting fees incurred connection with the offering. The Notes mature on June 1, 2025. At any time, or from time to time, prior to March 1, 2025, we may elect to redeem the Notes in whole or in part at a price based on 100% of the aggregate principal amount of any Notes redeemed plus the "Applicable Premium," plus accrued and unpaid interest thereon. Applicable Premium is defined as the greater of (1) 1.0% of the principal amount of the Notes, or (2) the principal value of the Notes plus the present value of all future interest payments. At any time on or after March 1, 2025, we may elect to redeem the Notes in whole or in part at a price equal to 100% of the aggregate principal amount of the Notes to be redeemed plus accrued and unpaid interest thereon. From time to time prior to June 1, 2022, we may also elect to use proceeds raised from one or more equity offerings to redeem up to 40% of the aggregate principal amount of the Notes at a price equal to 107.375% of the aggregate principal amount thereof plus accrued and unpaid interest thereon, subject to certain exceptions. Interest expense for the Notes includes interest and the amortization of capitalized debt issuance costs. In connection with the Notes offering, we recorded capitalized debt issuance costs of $7.4 million. Such amounts will be amortized over the contractual life of the Notes using the effective interest method. At September 30, 2021 and December 31, 2020, approximately $5.7 million and $6.7 million, respectively, of unamortized debt issuance costs remained. Interest expense for the nine months ended September 30, 2020 includes $2.6 million of costs related to the extinguishment of the 2018 Term Loan and the issuance of the Notes. At September 30, 2021 and December 31, 2020, $9.8 million and $2.5 million, respectively, of accrued and unpaid interest on the Notes was included in "Accounts Payable and Accrued Expenses" on our condensed consolidated balance sheet. 2020 Revolving Credit Facility On March 20, 2020, we amended our $85 million three-year secured revolving credit facility (the 2018 Revolving Credit Facility), increasing borrowing capacity under the facility to $100 million, extending its maturity date from May 24, 2021 to February 22, 2023, and reducing the interest cost related to both undrawn commitments and drawn borrowings under the facility (as amended, the 2020 Revolving Credit Facility). Borrowings under the 2020 Revolving Credit Facility may be used for general corporate purposes, including to support the growth of our new business production and operations, and accrue interest at a variable rate equal to, at our discretion, (i) a base rate (as defined in our existing credit agreement (the Credit Agreement), subject to a floor of 1.00% per annum) plus a margin of 0.375% to 1.875% per annum or (ii) the Eurodollar Rate plus a margin of 1.375% to 2.875% per annum, based on the applicable corporate credit rating at the time. On October 30, 2020, we entered into a Joinder Agreement to the Credit Agreement, increasing the aggregate principal amount of commitments under the 2020 Revolving Credit Facility from $100 million to $110 million. All other terms remained unchanged. As of September 30, 2021, no amounts were drawn under the 2020 Revolving Credit Facility. Under the 2020 Revolving Credit Facility, we are required to pay a quarterly commitment fee on the average daily undrawn amount of 0.175% to 0.525%, based on the applicable corporate credit rating at the time. As of September 30, 2021, the applicable commitment fee was 0.35%. For the three and nine months ended September 30, 2021, we recorded $0.1 million and $0.3 million of commitment fees in interest expense, respectively. We incurred debt issuance costs of $0.8 million in connection with the 2020 Revolving Credit Facility and had $0.6 million of unamortized debt issuance costs associated with the 2018 Revolving Credit Facility remaining at the time of its amendment and replacement. Combined unamortized debt issuance will be amortized through interest expense on a straight-line basis over the contractual life of the 2020 Revolving Credit Facility. At September 30, 2021, remaining unamortized deferred debt issuance costs were $0.7 million. We are subject to certain covenants under the 2020 Revolving Credit Facility, including, but not limited to, the following: a maximum debt-to-total capitalization ratio of 35%, a minimum liquidity requirement, compliance with the PMIERs' financial requirements (subject to any GSE approved waivers), and minimum consolidated net worth and statutory capital requirements (respectively, as defined therein). We were in compliance with all covenants at September 30, 2021.

Reinsurance

Reinsurance	9 Months Ended
	Sep. 30, 2021
Reinsurance Disclosures [Abstract]
Reinsurance	ReinsuranceWe enter into third-party reinsurance transactions to actively manage our risk, ensure compliance with PMIERs, state regulatory and other applicable capital requirements, (respectively, as defined therein), and support the growth of our business. The Wisconsin Office of the Commissioner of Insurance (Wisconsin OCI) has approved and the GSEs have indicated their non-objection to all such transactions (subject to certain conditions and ongoing review, including levels of approved capital credit). The effect of our reinsurance agreements on premiums written and earned is as follows: For the three months ended For the nine months ended September 30, 2021 September 30, 2020 September 30, 2021 September 30, 2020 (In Thousands) Net premiums written Direct $ 134,635 $ 119,323 $ 419,811 $ 331,254 Ceded (1) (22,704) (17,501) (65,423) (47,952) Net premiums written $ 111,931 $ 101,822 $ 354,388 $ 283,302 Net premiums earned Direct $ 137,159 $ 118,552 $ 399,005 $ 351,889 Ceded (1) (23,565) (19,750) (68,644) (55,426) Net premiums earned $ 113,594 $ 98,802 $ 330,361 $ 296,463 (1) Net of profit commission. Excess-of-loss reinsurance NMIC is party to reinsurance agreements with the Oaktown Re Vehicles that provide it with aggregate excess-of-loss reinsurance coverage on defined portfolios of mortgage insurance policies. Under each agreement, NMIC retains a first layer of aggregate loss exposure on covered policies and the respective Oaktown Re Vehicle then provides second layer loss protection up to a defined reinsurance coverage amount. NMIC then retains losses in excess of the respective reinsurance coverage amounts. NMIC makes risk premium payments to the Oaktown Re Vehicles for the applicable outstanding reinsurance coverage amount and pays an additional amount for anticipated operating expenses (capped at $250 thousand per year, except with respect to Oaktown Re Ltd., for which the cap is $300 thousand per year). NMIC ceded aggregate premiums to the Oaktown Re Vehicles of $10.4 million and $30.0 million during the three and nine months ended September 30, 2021, respectively, and $6.3 million and $13.4 million during the three and nine months ended September 30, 2020, respectively. The increase in premiums ceded during the respective periods year-on-year is due to the inception of the excess-of-loss reinsurance agreements that NMIC entered in with Oaktown Re IV Ltd., Oaktown Re V Ltd. and Oaktown Re VI Ltd. NMIC applies claims paid on covered policies against its first layer aggregate retained loss exposure under each excess-of-loss agreement. NMIC did not cede any incurred losses on covered policies to the Oaktown Re Vehicles during the three and nine months ended September 30, 2021 and 2020, as the aggregate first layer risk retention for each applicable agreement was not exhausted during such periods. Under the terms of each excess-of-loss reinsurance agreement, the Oaktown Re Vehicles are required to fully collateralize their outstanding reinsurance coverage amount to NMIC with funds deposited into segregated reinsurance trusts. Such trust funds are required to be invested in short-term U.S. Treasury money market funds at all times. Each Oaktown Re Vehicle financed its respective collateral requirement through the issuance of mortgage insurance-linked notes to unaffiliated investors. Such insurance-linked notes mature ten years from the inception date of each reinsurance agreement (except the notes issued by Oaktown Re VI Ltd. which have a 12.5 year maturity). We refer to NMIC's reinsurance agreements with and the insurance-linked note issuances by the Oaktown Re Vehicles individually as the 2017 ILN Transaction, 2018 ILN Transaction, 2019 ILN Transaction, 2020-1 ILN Transaction, 2020-2 ILN Transaction and 2021-1 ILN Transaction, and collectively as the ILN Transactions. The respective reinsurance coverage amounts provided by the Oaktown Re Vehicles decrease over a ten-year period as the underlying insured mortgages are amortized or repaid, and/or the mortgage insurance coverage is canceled (except the coverage provided by Oaktown Re VI Ltd., which decreases over a 12.5 year period). As the reinsurance coverage decreases, a prescribed amount of collateral held in trust by the Oaktown Re Vehicles is distributed to ILN Transaction noteholders as amortization of the outstanding insurance-linked note principal balances. The outstanding reinsurance coverage amounts stop amortizing, and the collateral distribution to ILN Transaction noteholders and amortization of insurance-linked note principal is suspended if certain credit enhancement or delinquency thresholds, as defined in each agreement, are triggered (each, a Lock-Out Event). A Lock-Out Event was deemed to have occurred, effective June 25, 2020 for each of the 2017, 2018 and 2019 ILN Transactions (related to the default experience of the underlying reference pools for each respective transaction) and at inception of the 2021-1 ILN Transaction (related to the initial build of its target credit enhancement), and the amortization of reinsurance coverage, and distribution of collateral assets and amortization of insurance-linked notes was suspended for each ILN Transaction. The amortization of reinsurance coverage, distribution of collateral assets and amortization of insurance-linked notes will remain suspended for the duration of the Lock-Out Event for each ILN Transaction, and during such period assets will be preserved in the applicable reinsurance trust account to collateralize the excess-of-loss reinsurance coverage provided to NMIC. The following table presents the inception date, covered production p eriod, initial and current reinsurance coverage amount, and initial and current first layer retained aggregate loss under each of the ILN Transactions. Current amounts are presented as of September 30, 2021. ( $ values in thousands) Inception Date Covered Production Initial Reinsurance Coverage Current Reinsurance Coverage Initial First Layer Retained Loss Current First Layer Retained Loss (1) 2017 ILN Transaction May 2, 2017 1/1/2013 - 12/31/2016 $211,320 $40,226 $126,793 $121,196 2018 ILN Transaction July 25, 2018 1/1/2017 - 5/31/2018 264,545 158,489 125,312 122,750 2019 ILN Transaction July 30, 2019 6/1/2018 - 6/30/2019 326,905 231,877 123,424 122,697 2020-1 ILN Transaction July 30, 2020 7/1/2019 - 3/31/2020 322,076 84,470 169,514 169,488 2020-2 ILN Transaction October 29, 2020 4/1/2020 - 9/30/2020 (2) 242,351 177,566 121,777 121,177 2021-1 ILN Transaction (4) April 27, 2021 10/1/2020 - 3/31/2021 (3) 367,238 367,238 163,708 163,708 (1) NMIC applies claims paid on covered policies against its first layer aggregate retained loss exposure and cedes reserves for incurred claims and claims expenses to each applicable ILN Transaction and recognizes a reinsurance recoverable if such incurred claims and claims expenses exceed its current first layer retained loss. (2) Approximately 1% of the production covered by the 2020-2 ILN Transaction has coverage reporting dates between July 1, 2019 and March 31, 2020. (3) Approximately 1% of the production covered by the 2021-1 ILN Transaction has coverage reporting dates between July 1, 2019 and September 30, 2020. (4) As of September 30, 2021, the current reinsurance coverage amount on the 2021-1 ILN transaction is equal to the initial reinsurance coverage, as the reinsurance coverage provided by Oaktown Re will not decrease until its target credit enhancement is met. NMIC holds optional termination rights under each ILN Transaction, including, among others, an optional call feature which provides NMIC the discretion to terminate the transaction on or after a prescribed date, and a clean-up call if the outstanding reinsurance coverage amount amortizes to 10% or less of the reinsurance coverage amount at inception or if NMIC reasonably determines that changes to GSE or rating agency asset requirements would cause a material and adverse effect on the capital treatment afforded to NMIC under a given agreement. In addition, there are certain events that trigger mandatory termination of an agreement, including NMIC's failure to pay premiums or consent to reductions in a trust account to make principal payments to noteholders, among others. Under the terms of the 2018, 2019 and 2020-1 ILN Transactions, we are required to maintain a certain level of restricted funds in premium deposit accounts with Bank of New York Mellon until the respective notes have been redeemed in full. "Cash and cash equivalents" on our condensed consolidated balance sheet includes restricted amounts of $3.6 million and $5.6 million as of September 30, 2021 and December 31, 2020, respectively. We are not required to deposit additional funds into the premium deposit accounts in the future and the restricted balances required under these transactions will decline over time as the outstanding principal balance of the respective insurance-linked notes are amortized. Quota share reinsurance NMIC is party to four outstanding quota share reinsurance treaties - the 2016 QSR Transaction, effective September 1, 2016, the 2018 QSR Transaction, effective January 1, 2018, the 2020 QSR Transaction, effective April 1, 2020, and the 2021 QSR Transaction, effective January 1, 2021 - which we refer to collectively as the QSR Transactions. Under each of the QSR Transactions, NMIC cedes a proportional share of its risk on eligible policies written during a discrete period to panels of third-party reinsurance providers. Each of the third-party reinsurance providers has an insurer financial strength rating of A- or better by Standard & Poor's Rating Service (S&P), A.M. Best Company, Inc. (A.M. Best) or both. Under the terms of the 2016 QSR Transaction, NMIC cedes premiums written related to 25% of the risk on eligible primary policies written for all periods through December 31, 2017 and 100% of the risk under our pool agreement with Fannie Mae. The 2016 QSR Transaction is scheduled to terminate on December 31, 2027, except with respect to the ceded pool risk, which is scheduled to terminate on August 31, 2023. NMIC has the option, based on certain conditions and subject to a termination fee, to terminate the agreement as of December 31, 2020, or at the end of any calendar quarter thereafter, which would result in NMIC recapturing the related risk. Under the terms of the 2018 QSR Transaction, NMIC cedes premiums earned related to 25% of the risk on eligible policies written in 2018 and 20% of the risk on eligible policies written in 2019. The 2018 QSR Transaction is scheduled to terminate on December 31, 2029. NMIC has the option, based on certain conditions and subject to a termination fee, to terminate the agreement as of December 31, 2022, or at the end of any calendar quarter thereafter, which would result in NMIC recapturing the related risk. Under the terms of the 2020 QSR Transaction, NMIC cedes premiums earned related to 21% of the risk on eligible policies written from April 1, 2020 to December 31, 2020. The 2020 QSR Transaction is scheduled to terminate on December 31, 2030. NMIC has the option, based on certain conditions and subject to a termination fee, to terminate the agreement as of December 31, 2023, or at the end of any calendar quarter thereafter, which would result in NMIC recapturing the related risk. Under the terms of the 2021 QSR Transaction, NMIC cedes premiums earned related to 22.5% of the risk on eligible policies written in 2021 (subject to an aggregate risk written limit). The 2021 QSR Transaction is scheduled to terminate on December 31, 2031. NMIC has the option, based on certain conditions and subject to a termination fee, to terminate the agreement as of December 31, 2024, or at the end of any calendar quarter thereafter, which would result in NMIC recapturing the related risk. NMIC may terminate any or all of the QSR Transactions without penalty if, due to a change in PMIERs requirements, it is no longer able to take full PMIERs asset credit for the risk-in-force (RIF) ceded under the respective agreements. Additionally, under the terms of the QSR Transactions, NMIC may elect to selectively terminate its engagement with individual reinsurers on a run-off basis ( i.e. , reinsurers continue providing coverage on all risk ceded prior to the termination date, with no new cessions going forward) or cut-off basis ( i.e. , the reinsurance arrangement is completely terminated with NMIC recapturing all previously ceded risk) under certain circumstances. Such selective termination rights arise when, among other reasons, a reinsurer experiences a deterioration in its capital position below a prescribed threshold and/or a reinsurer breaches (and fails to cure) its collateral posting obligations under the relevant agreement. Effective April 1, 2019, NMIC elected to terminate its engagement with one reinsurer under the 2016 QSR Transaction on a cut-off basis. In connection with the termination, NMIC recaptured approximately $500 million of previously ceded primary RIF and stopped ceding new premiums earned or written with respect to the recaptured risk. With the termination, ceded premiums written under the 2016 QSR Transaction decreased from 25% to 20.5% on eligible policies. The termination has no effect on the cession of pool risk under the 2016 QSR Transaction. The following table shows amounts related to the QSR Transactions: For the three months ended For the nine months ended September 30, 2021 September 30, 2020 September 30, 2021 September 30, 2020 (In Thousands) Ceded risk-in-force $ 7,610,870 $ 5,159,061 $ 7,610,870 $ 5,159,061 Ceded premiums earned (28,366) (24,517) (81,650) (70,738) Ceded claims and claim expenses 840 3,200 3,214 13,401 Ceding commission earned 6,142 4,798 17,265 13,739 Profit commission 15,191 11,034 42,962 28,718 Ceded premiums written under the 2016 QSR Transaction are recorded on the balance sheet as prepaid reinsurance premiums and amortized to ceded premiums earned in a manner consistent with the recognition of revenue on direct premiums. Under the 2018, 2020 and 2021 QSR Transactions, premiums are ceded on an earned basis as defined in the agreement. NMIC receives a 20% ceding commission for premiums ceded under the QSR Transactions. NMIC also receives a profit commission under each of the QSR Transactions, provided that the loss ratios on loans covered under the 2016 QSR Transaction, 2018 QSR Transaction, 2020 QSR Transaction and 2021 QSR Transaction, generally remain below 60%, 61%, 50% and 57.5%, respectively, as measured annually. Ceded claims and claim expenses under each of the QSR Transactions reduce the respective profit commission received by NMIC on a dollar-for-dollar basis. In accordance with the terms of the 2016 QSR Transaction, rather than making a cash payment or transferring investments for ceded premiums written, NMIC established a funds withheld liability, which also includes amounts due to NMIC for ceding and profit commissions. Any loss recoveries and any potential profit commission to NMIC will be realized from this account until exhausted. NMIC's reinsurance recoverable balance is further supported by trust accounts established and maintained by each reinsurer in accordance with the PMIERs funding requirements for risk ceded to non-affiliates. The reinsurance recoverable on loss reserves related to the 2016 QSR Transaction was $4.8 million as of September 30, 2021. In accordance with the terms of the 2018, 2020 and 2021 QSR Transactions, cash payments for ceded premiums earned are settled on a quarterly basis, offset by amounts due to NMIC for ceding and profit commissions. Any loss recoveries and any potential profit commission to NMIC are also recognized quarterly. NMIC's reinsurance recoverable balance is supported by trust accounts established and maintained by each reinsurer in accordance with the PMIERs funding requirements for risk ceded to non-affiliates. The aggregate reinsurance recoverable on loss reserves related to the 2018, 2020 and 2021 QSR Transactions was $15.6 million as of September 30, 2021. We remain directly liable for all claim payments if we are unable to collect reinsurance recoverable due from our reinsurers and, as such, we actively monitor and manage our counterparty credit exposure to our reinsurance providers. We establish an allowance for expected credit loss against our reinsurance recoverable if we do not expect to recover amounts due from one or more of our reinsurance counterparties, and report our reinsurance recoverable net of such allowance, if any. We actively monitor the counterparty credit profiles of our reinsurers and each is required to partially collateralize its obligations under the terms of our QSR Transactions. As of September 30, 2021, we did not recognize any allowance for credit loss with respect to our reinsurance recoverable.

Reserves for Insurance Claims a

Reserves for Insurance Claims and Claim Expenses	9 Months Ended
	Sep. 30, 2021
Insurance [Abstract]
Reserves for Insurance Claims and Claim Expenses	Reserves for Insurance Claims and Claim Expenses We hold gross reserves in an amount equal to the estimated liability for insurance claims and claim expenses related to defaults on insured mortgage loans. A loan is considered to be in "default" as of the payment date at which a borrower has missed the preceding two or more consecutive monthly payments. We establish reserves for loans that have been reported to us in default by servicers, referred to as case reserves, and additional loans that we estimate (based on actuarial review and other factors) to be in default that have not yet been reported to us by servicers, referred to as incurred but not reported (IBNR) reserves. We also establish reserves for claim expenses, which represent the estimated cost of the claim administration process, including legal and other fees, as well as other general expenses of administering the claim settlement process. As of September 30, 2021, we had 7,670 primary loans in default and held gross reserves for insurance claims and claim expenses of $104.6 million. During the nine months ended September 30, 2021, we paid 59 claims totaling $2.0 million, including 57 claims covered under the QSR Transactions representing $0.4 million of ceded claims and claim expenses. In 2013, we entered into a pool insurance transaction with Fannie Mae. The pool transaction includes a deductible, which represents the amount of claims to be absorbed by Fannie Mae before we are obligated to pay any claims. We only establish reserves for pool risk if we expect claims to exceed this deductible. At September 30, 2021, 121 loans in the pool were in default. These 121 loans represented approximately $9.9 million of RIF. Due to the size of the remaining deductible, our expectation that a limited number of loans in default will progress to a claim and the expected severity on such claim submissions (all loans in the pool had loan-to-value (LTV) ratios under 80% at origination), we did not establish any case or IBNR reserves for pool risk at September 30, 2021. In connection with the settlement of pool claims, we applied $1.0 million to the pool deductible through September 30, 2021. At September 30, 2021, the remaining pool deductible was $9.4 million. We have not paid any pool claims to date. 100% of our pool RIF is reinsured under the 2016 QSR Transaction. We had 7,670 loans in default in our primary insured portfolio as of September 30, 2021, which represented a 1.56% default rate against 490,714 to tal policies in-force. We had 13,765 loans in default in our primary insured portfolio as of September 30, 2020, which represented a 3.60% default rate against 381,899 total policies in-force. Although our default count declined from September 30, 2020 to September 30, 2021, the population remains elevated compared to our historical experience due to the continued challenges certain borrowers are facing related to the COVID-19 outbreak and their decision to access the forbearance program for federally backed loans codified under the Coronavirus Aid, Relief and Economic Security (CARES) Act or similar programs made available by private lenders. The size of the reserve we establish for each defaulted loan (and by extension our aggregate reserve for claims and claim expenses) reflects our best estimate of the future claim payment to be made for each individual loan in default. Our future claims exposure is a function of the number of defaulted loans that progress to claim payment (which we refer to as frequency) and the amount to be paid to settle such claims (which we refer to as severity). Our estimates of claims frequency and severity are not formulaic, rather they are broadly synthesized based on historical observed experience for similarly situated loans and assumptions about future macroeconomic factors. We generally observe that forbearance programs are an effective tool to bridge dislocated borrowers from a time of acute stress to a future date when they can resume timely payment of their mortgage obligations. The effectiveness of forbearance programs is enhanced by the availability of various repayment and loan modification options which allow borrowers to amortize or, in certain instances, outright defer payments otherwise due during the forbearance period over an extended length of time. In response to the COVID-19 outbreak, the Federal Housing Financing Agency (FHFA) and GSEs introduced new repayment and loan modification options to further assist borrowers with their transition out of forbearance programs and default status. Our reserve setting process considers the beneficial impact of forbearance, foreclosure moratorium and other assistance programs available to defaulted borrowers. At September 30, 2020 and 2021, we generally established lower reserves for defaults that we consider to be connected to the COVID-19 outbreak given our expectation that forbearance, repayment and modification, and other assistance programs will aid affected borrowers and drive higher cure rates on such defaults than we would otherwise expect to experience on similarly situated loans that did not benefit from broad-based assistance programs. The following table provides a reconciliation of the beginning and ending gross reserve balances for primary insurance claims and claim expenses: For the nine months ended September 30, 2021 2020 (In Thousands) Beginning balance $ 90,567 $ 23,752 Less reinsurance recoverables (1) (17,608) (4,939) Beginning balance, net of reinsurance recoverables 72,959 18,813 Add claims incurred: Claims and claim expenses incurred: Current year (2) 19,275 61,198 Prior years (3) (6,469) (5,500) Total claims and claim expenses incurred 12,806 55,698 Less claims paid: Claims and claim expenses paid: Current year (2) 15 152 Prior years (3) 1,566 4,309 Total claims and claim expenses paid 1,581 4,461 Reserve at end of period, net of reinsurance recoverables 84,184 70,050 Add reinsurance recoverables (1) 20,420 17,180 Ending balance $ 104,604 $ 87,230 (1) Related to ceded losses recoverable under the QSR Transactions. See Note 5, " Reinsurance " for additional information. (2) Related to insured loans with their most recent defaults occurring in the current year. For example, if a loan defaulted in a prior year and subsequently cured and later re-defaulted in the current year, the default would be included in the current year. Amounts are presented net of reinsurance and included $14.0 million attributed to net case reserves and $4.8 million attributed to net IBNR reserves for the nine months ended September 30, 2021 and $55.4 million attributed to net case reserves and $4.8 million attributed to net IBNR reserves for the nine months ended September 30, 2020. (3) Related to insured loans with defaults occurring in prior years, which have been continuously in default before the start of the current year. Amounts are presented net of reinsurance and included $1.8 million attributed to net case reserves and $5.0 million attributed to net IBNR reserves for the nine months ended September 30, 2021 and $4.0 million attributed to net case reserves and $1.3 million attributed to net IBNR reserves for the nine months ended September 30, 2020. The "claims incurred" section of the table above shows claims and claim expenses incurred on defaults occurring in current and prior years, including IBNR reserves and is presented net of reinsurance. We may increase or decrease our claim estimates and reserves as we learn additional information about individual defaulted loans, and continue to observe and analyze loss development trends in our portfolio. Gross reserves of $80.6 million related to prior year defaults remained as of September 30, 2021.

Earnings per Share (EPS)

Earnings per Share (EPS)	9 Months Ended
	Sep. 30, 2021
Earnings Per Share [Abstract]
Earnings per Share (EPS)	Earnings per Share (EPS) Basic EPS is based on the weighted average number of shares of common stock outstanding. Diluted EPS is based on the weighted average number of shares of common stock outstanding and common stock equivalents that would be issuable upon the vesting of service based and performance and service-based restricted stock units (RSUs), and the exercise of vested and unvested stock options and outstanding warrants. The number of shares issuable for RSUs subject to performance and service based vesting requirements are only included in diluted shares if the relevant performance measurement period has commenced and results during such period meet the necessary performance criteria. The following table reconciles the net income and the weighted average shares of common stock outstanding used in the computations of basic and diluted EPS of common stock. For the three months ended September 30, For the nine months ended September 30, 2021 2020 2021 2020 (In Thousands, except for per share data) Net income $ 60,193 $ 38,179 $ 170,606 $ 123,298 Basic weighted average shares outstanding 85,721 84,805 85,563 75,695 Basic earnings per share $ 0.70 $ 0.45 $ 1.99 $ 1.63 Net income $ 60,193 $ 38,179 $ 170,606 $ 123,298 Gain from change in fair value of warrant liability — — (454) (4,286) Diluted net income $ 60,193 $ 38,179 $ 170,152 $ 119,012 Basic weighted average shares outstanding 85,721 84,805 85,563 75,695 Dilutive effect of issuable shares 1,159 794 1,231 1,172 Diluted weighted average shares outstanding 86,880 85,599 86,794 76,867 Diluted earnings per share $ 0.69 $ 0.45 $ 1.96 $ 1.55 Anti-dilutive shares 1 420 2 91

Warrants

Warrants	9 Months Ended
	Sep. 30, 2021
Debt Disclosure [Abstract]
Warrants	Warrants We issued 992 thousand warrants in connection with a private placement of our common stock in April 2012, of which 239 thousand remained outstanding available for exercise at September 30, 2021. Each warrant gives the holder thereof the right to purchase one share of common stock at an exercise price equal to $10.00. The warrants were issued with an aggregate fair value of $5.1 million. During the three months ended September 30, 2021, 32 thousand warrants were exercised resulting in the issuance of 28 thousand shares of common stock. Upon exercise, we reclassified approximately $0.4 million of warrant fair value from warrant liability to additional paid-in capital. During the nine months ended September 30, 2021, 73 thousand warrants were exercised resulting in the issuance of 60 thousand shares of common stock. Upon exercise, we reclassified approximately $0.9 million of warrant fair value from warrant liability to additional paid-in capital. During the three months ended September 30, 2020, no warrants were exercised. During the nine months ended September 30, 2020, nine thousand warrants were exercised resulting in the issuance of six thousand shares of common stock. Upon exercise, we reclassified approximately $0.2 million of warrant fair value from warrant liability to additional paid-in capital.

Income Taxes

Income Taxes	9 Months Ended
	Sep. 30, 2021
Income Tax Disclosure [Abstract]
Income Taxes	Income Taxes We are a U.S. taxpayer and are subject to a statutory U.S. federal corporate income tax rate of 21%. NMIH files a consolidated U.S. federal and various state income tax returns on behalf of itself and its subsidiaries. Our effective tax rate on our pre-tax income was 22.3% and 21.9% for the three and nine months ended September 30, 2021, respectively, compared to 22.6% and 21.2% for the three and nine months ended September 30, 2020, respectively. Our provision for income taxes for interim reporting periods is established based on our estimated annual effective tax rate for a given year. Our effective tax rate may fluctuate between interim periods due to the impact of discrete items not included in our estimated annual effective tax rate, including the tax effects associated with the vesting of RSUs and exercise of options, and the change in fair value of our warrant liability. Such items are treated on a discrete basis in the reporting period in which they occur. As a mortgage guaranty insurance company, we are eligible to claim a tax deduction for our statutory contingency reserve balance, subject to certain limitations outlined under IRC Section 832(e), and only to the extent we acquire tax and loss bonds in an amount equal to the tax benefit derived from the claimed deduction, which is our intent. As a result, our interim provision for income taxes for the three and nine months ended September 30, 2021 represents a change in our net deferred tax

Premium Receivable

Premium Receivable	9 Months Ended
	Sep. 30, 2021
Insurance [Abstract]
Premium Receivable	Premium Receivable Premiums receivable consists of premiums due on our mortgage insurance policies. If a mortgage insurance premium is unpaid for more than 120 days, all associated receivables are written off against earned premium and the related insurance policy is canceled. We recognize an allowance for credit losses for premiums receivable based on credit losses expected to arise over the life of the receivable. Due to the nature of our insurance policies (a necessary precondition for access to mortgage credit for covered borrowers) and the short duration of the related receivables, we do not typically experience credit losses against our premium receivables and did not establish an allowance for credit loss at September 30, 2021 and December 31, 2020. Premiums receivable may be written off prior to 120 days in the ordinary course of business for non-credit events including, but not limited to, the modification or refinancing of an underlying insured loan. We establish a reserve for the write-off of premiums receivable based on historical experience. Our premium write-off reserve was not material at September 30, 2021 or December 31, 2020.

Regulatory Information

Regulatory Information	9 Months Ended
	Sep. 30, 2021
Insurance [Abstract]
Regulatory Information	Regulatory Information Statutory Requirements Our insurance subsidiaries, NMIC and Re One, file financial statements in conformity with statutory accounting principles (SAP) prescribed or permitted by the Wisconsin OCI, NMIC's principal regulator. Prescribed SAP includes state laws, regulations and general administrative rules, as well as a variety of publications of the National Association of Insurance Commissioners (NAIC). The Wisconsin OCI recognizes only statutory accounting practices prescribed or permitted by the state of Wisconsin for determining and reporting the financial condition and results of operations of an insurance company and for determining its solvency under Wisconsin insurance laws. NMIC and Re One generated combined statutory net income of $8.7 million and $23.9 million for the three and nine months ended September 30, 2021, respectively, and combined statutory net loss of $5.6 million and $22.6 million for the three and nine months ended September 30, 2020, respectively. The Wisconsin OCI has imposed a prescribed accounting practice for the treatment of statutory contingency reserves that differs from the treatment promulgated by the NAIC. Under Wisconsin OCI's prescribed practice mortgage guaranty insurers are required to reflect changes in their contingency reserves through statutory income. Such approach contrasts with the NAIC's treatment, which records changes to contingency reserves directly to unassigned funds. As a Wisconsin-domiciled insurer, NMIC's statutory net income reflects an expense associated with the change in its contingency reserve. While such treatment impacts NMIC's statutory net income, it does not have an effect on NMIC's statutory capital position. The following table presents NMIC and Re One's combined statutory surplus, contingency reserve, statutory capital and risk-to-capital (RTC) ratio: September 30, 2021 December 31, 2020 (In Thousands) Statutory surplus $ 913,471 $ 894,331 Contingency reserve 967,826 768,324 Statutory capital (1) $ 1,881,297 $ 1,662,655 Risk-to-capital 12.5:1 11.7:1 (1) Represents the total of the statutory surplus and contingency reserve. NMIH is not subject to any limitations on its ability to pay dividends except those generally applicable to corporations that are incorporated in the State of Delaware. Delaware law provides that dividends are only payable out of a corporation's capital surplus or, subject to certain limitations, recent net profits. NMIC and Re One are subject to certain rules and regulations prescribed by jurisdictions in which they are authorized to operate and the GSEs that may restrict their ability to pay dividends to NMIH. Re One has the capacity to pay $1.6 million of aggregate ordinary dividends to NMIH during the twelve-month period ending December 31, 2021. NMIC reported a statutory net loss for the year ended December 31, 2020 and does not have the capacity to pay dividends to NMIH during the twelve-month period ended December 31, 2021 without prior approval from the Wisconsin OCI. Neither Re One nor NMIC have ever paid dividends to NMIH. As an approved insurer under PMIERs, NMIC would generally be subject to prior GSE approval of its ability to pay dividends to NMIH if it failed to meet the financial requirements prescribed by PMIERs. In response to the COVID-19 pandemic, the GSEs issued temporary PMIERs guidance, effective for the period from June 30, 2020 to June 30, 2021, that requires approved insurers to secure approval from the GSEs prior to paying any dividends, even if the approved insurer otherwise satisfies the financial requirements prescribed by PMIERs. On June 30, 2021, the GSEs updated the temporary PMIERs guidance to permit approved insurers to pay dividends without securing prior approval if certain prescribed financial requirements are met during the period from July 1, 2021 to December 31, 2021.

Subsequent Event

Subsequent Event	9 Months Ended
	Sep. 30, 2021
Subsequent Events [Abstract]
Subsequent Event	Subsequent Event Excess-of-loss reinsurance On October 26, 2021, NMIC entered into a reinsurance agreement with Oaktown Re VII Ltd. (Oaktown Re VII), a Bermuda domiciled special purpose reinsurer, that provides for up to $363.6 million of aggregate excess-of-loss reinsurance coverage at inception for new delinquencies on an existing portfolio of mortgage insurance policies primarily written between April 1, 2021 and September 30, 2021. For the reinsurance coverage period, NMIC will retain the first layer of $146.2 million of aggregate losses and Oaktown Re VII will then provide second layer coverage up to the outstanding reinsurance coverage amount. NMIC will then retain losses in excess of the outstanding reinsurance coverage amount. Oaktown Re VII financed the coverage by issuing mortgage insurance-linked notes in an aggregate principal amount of $363.6 million to unaffiliated investors. The notes issued by Oaktown Re VII mature on April 25, 2034; all proceeds raised were deposited into a reinsurance trust to collateralize and fund the obligations of Oaktown Re VII to NMIC under the reinsurance agreement. Funds in the reinsurance trust account are required to be invested in high credit quality money market funds at all times. We refer to NMIC's reinsurance agreement with and the insurance-linked notes issued by Oaktown Re VII as the 2021-2 ILN Transaction. Under the terms of the 2021-2 ILN Transaction, NMIC makes risk premium payments for the applicable outstanding reinsurance coverage amount and pays Oaktown Re VII for anticipated operating expenses (capped at $250,000 per year). Quota share reinsurance In October 2021, NMIC entered into two back-to-back quota share reinsurance treaties that will provide coverage for mortgage insurance policies to be written primarily in 2022 and 2023 (the “2022 QSR Transaction” and “2023 QSR Transaction”). Under the terms of the 2022 and 2023 QSR Transactions, NMIC will cede premiums earned related to 20% of the risk on eligible policies written between January 1, 2022 and December 31, 2023, in exchange for reimbursement of ceded claims and claims expenses on covered policies, a 20% ceding commission, and a profit commission of up to 62% that varies directly and inversely with ceded claims. If NMIC exhausts the aggregate risk written limit of the 2021 QSR Transaction prior to December 31, 2021, the 2022 QSR Transaction will automatically incept and NMIC will begin to cede risk on eligible policies under the treaty prior to January 1, 2022.

Organization, Basis of Presen_2

Organization, Basis of Presentation and Summary of Accounting Principles (Policies)	9 Months Ended
	Sep. 30, 2021
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Basis of Presentation	Basis of Presentation The accompanying unaudited condensed consolidated financial statements, which include the results of NMIH and its wholly-owned subsidiaries, have been prepared in accordance with the instructions to Form 10-Q as prescribed by the SEC for interim reporting and include other information and disclosures required by accounting principles generally accepted in the U.S. (GAAP). Our accounts are maintained in U.S. dollars. These statements should be read in conjunction with our consolidated financial statements and notes thereto for the year ended December 31, 2020, included in our 2020 10-K. All intercompany transactions have been eliminated. The preparation of financial statements in accordance with GAAP requires management to make estimates and assumptions that affect reported amounts of assets and liabilities, as well as disclosure of contingent assets and liabilities as of the balance sheet date. Estimates also affect the reported amounts of income and expenses for the reporting period. Actual results could differ from those estimates. The results of operations for the interim period may not be indicative of the results that may be expected for the full year ending December 31, 2021.
Variable Interest Entities	Variable Interest Entities NMIC is a party to reinsurance agreements with Oaktown Re Ltd., Oaktown Re II Ltd., Oaktown Re III Ltd., Oaktown Re IV Ltd. Oaktown Re V Ltd., and Oaktown Re VI Ltd. (special purpose reinsurance entities collectively referred to as the Oaktown Re Vehicles) effective May 2, 2017, July 25, 2018, July 30, 2019, July 30, 2020, October 29, 2020 and April 27, 2021, respectively. At inception of the respective reinsurance agreements, we determined that each of the Oaktown Re Vehicles were variable interest entities (VIEs), as defined under GAAP Accounting Standards Codification (ASC) 810, because they did not have sufficient equity at risk to finance their respective activities. We evaluated the VIEs at inception to determine whether NMIC was the primary beneficiary under each reinsurance transaction and, if so, whether we were required to consolidate the assets and liabilities of each VIE. The primary beneficiary of a VIE is an enterprise that (1) has the power to direct the activities of the VIE, which most significantly impact its economic performance and (2) has significant economic exposure to the VIE, i.e. , the obligation to absorb losses or receive benefits that could potentially be significant. The determination of whether an entity is the primary beneficiary of a VIE is complex and requires management judgment regarding determinative factors, including the expected results of the VIE and how those results are absorbed by beneficial interest holders, as well as which party has the power to direct activities that most significantly impact the performance of the VIE. We concluded that we are not the primary beneficiary of each VIE and, as such, we do not consolidate them in our consolidated financial statements.
Recent Accounting Pronouncements	Recent Accounting Pronouncements - Adopted In December 2019, the Financial Accounting Standards Board (the FASB) issued ASU 2019-12, Simplifying the Accounting for Income Taxes (Topic 740). The update eliminates certain exceptions for recognizing deferred taxes for investments, performing intra-period allocations and calculating income taxes in interim periods. The ASU also includes guidance to reduce complexity in certain income tax areas, including recognizing deferred taxes for tax goodwill and allocating taxes to members of a consolidated group. We adopted this ASU on January 1, 2021 and determined it did not have a material impact on our consolidated financial statements. Recent Accounting Pronouncements - Not Yet Adopted In August 2018, the FASB issued ASU 2018-12, Targeted Improvements to the Accounting for Long-Duration Contracts (Topic 944). The update provides guidance to the existing recognition, measurement, presentation and disclosure requirements for long-duration contracts issued by an insurance entity. The FASB subsequently issued ASU 2019-09 in November 2019 and ASU 2020-11 in November 2020, which amended the effective date for this standard and provided transition relief to facilitate early application for long duration contracts. These standards will now take effect for public business entities for fiscal years, and interim periods within those fiscal years, beginning after December 15, 2022. We are currently evaluating the impact the adoption of these ASUs will have, if any, on our consolidated financial statements. In March 2020, the FASB issued ASU 2020-04, Reference Rate Reform (Topic 848). The update provides optional guidance to ease the potential burden in accounting for reference rate reform on financial reporting. Reference rate reform refers to the global transition away from referencing the London Interbank Offered Rate (LIBOR) in financial contracts, which is expected to be discontinued beginning in 2021 through 2023. The ASU includes optional expedients and exceptions for applying GAAP to contracts, hedging relationships and other transactions affected by reference rate reform if certain criteria are met. This standard may be elected and applied prospectively over time from March 12, 2020 through December 31, 2022 as reference rate reform activities occur. The adoption of, and future elections under, this ASU are not expected to have a material impact on our consolidated financial statements as the ASU will ease, if warranted, the requirements for accounting for the future effects of the rate reform. We continue to monitor the impact the discontinuance of LIBOR or another reference rate will have on our contracts and other transactions. In August 2020, the FASB issued ASU 2020-06, Debt—Debt with Conversion and Other Options (Subtopic 470-20) and Derivatives and Hedging— Contracts in Entity's Own Equity (Subtopic 815-40 ). This update simplifies the accounting for convertible instruments and contracts on an entity's own equity, including warrants, eliminating certain triggers for derivative accounting. The standard will take effect for public business entities for fiscal years, and interim periods within those fiscal years, beginning after December 15, 2021. We have evaluated the impact the adoption of this ASU and we do not expect it to have a material impact on our consolidated financial statements, including our warrant liability.
Earnings Per Share	Basic EPS is based on the weighted average number of shares of common stock outstanding. Diluted EPS is based on the weighted average number of shares of common stock outstanding and common stock equivalents that would be issuable upon the vesting of service based and performance and service-based restricted stock units (RSUs), and the exercise of vested and unvested stock options and outstanding warrants. The number of shares issuable for RSUs subject to performance and service based vesting requirements are only included in diluted shares if the relevant performance measurement period has commenced and results during such period meet the necessary performance criteria. The following table reconciles the net income and the weighted average shares of common stock outstanding used in the computations of basic and diluted EPS of common stock.
Premiums Receivable	Premium Receivable Premiums receivable consists of premiums due on our mortgage insurance policies. If a mortgage insurance premium is unpaid for more than 120 days, all associated receivables are written off against earned premium and the related insurance policy is canceled. We recognize an allowance for credit losses for premiums receivable based on credit losses expected to arise over the life of the receivable. Due to the nature of our insurance policies (a necessary precondition for access to mortgage credit for covered borrowers) and the short duration of the related receivables, we do not typically experience credit losses against our premium receivables and did not establish an allowance for credit loss at September 30, 2021 and December 31, 2020. Premiums receivable may be written off prior to 120 days in the ordinary course of business for non-credit events including, but not limited to, the modification or refinancing of an underlying insured loan. We establish a reserve for the write-off of premiums receivable based on historical experience. Our premium write-off reserve was not material at September 30, 2021 or December 31, 2020.

Investments (Tables)

Investments (Tables)	9 Months Ended
	Sep. 30, 2021
Investments, Debt and Equity Securities [Abstract]
Schedule of fair values and gross unrealized gains and losses	Fair Values and Gross Unrealized Gains and Losses on Investments Amortized Gross Unrealized Fair Gains Losses As of September 30, 2021 (In Thousands) U.S. Treasury securities and obligations of U.S. government agencies $ 29,435 $ 1,384 $ — $ 30,819 Municipal debt securities 503,615 8,114 (2,735) 508,994 Corporate debt securities 1,375,589 32,051 (10,478) 1,397,162 Asset-backed securities 104,990 1,516 (77) 106,429 Total bonds 2,013,629 43,065 (13,290) 2,043,404 Short-term investments 11,010 5 — 11,015 Total investments $ 2,024,639 $ 43,070 $ (13,290) $ 2,054,419 Amortized Gross Unrealized Fair Gains Losses As of December 31, 2020 (In Thousands) U.S. Treasury securities and obligations of U.S. government agencies $ 29,412 $ 2,186 $ — $ 31,598 Municipal debt securities 407,323 14,027 (2) 421,348 Corporate debt securities 1,165,260 55,014 (483) 1,219,791 Asset-backed securities 128,471 2,736 (27) 131,180 Total bonds 1,730,466 73,963 (512) 1,803,917 Short-term investments 369 — — 369 Total investments $ 1,730,835 $ 73,963 $ (512) $ 1,804,286
Schedule of investments by industry group	The following table presents a breakdown of the fair value of our corporate debt securities by issuer industry group as of September 30, 2021 and December 31, 2020: September 30, 2021 December 31, 2020 Financial 38 % 37 % Consumer 23 23 Communications 12 10 Technology 10 10 Utilities 10 11 Industrial 7 9 Total 100 % 100 %
Schedule of investments by maturity	The amortized cost and fair value of available-for-sale securities as of September 30, 2021 and December 31, 2020, by contractual maturity, are shown below. Expected maturities will differ from contractual maturities because issuers may have the right to call or prepay obligations with or without call or prepayment penalties. Because most asset-backed securities provide for periodic payments throughout their lives, they are listed below in a separate category. As of September 30, 2021 Amortized Fair (In Thousands) Due in one year or less $ 66,077 $ 66,624 Due after one through five years 624,658 646,757 Due after five through ten years 1,165,336 1,170,933 Due after ten years 63,578 63,676 Asset-backed securities 104,990 106,429 Total investments $ 2,024,639 $ 2,054,419 As of December 31, 2020 Amortized Fair (In Thousands) Due in one year or less $ 57,429 $ 57,949 Due after one through five years 507,444 536,520 Due after five through ten years 1,016,230 1,056,098 Due after ten years 21,261 22,539 Asset-backed securities 128,471 131,180 Total investments $ 1,730,835 $ 1,804,286
Schedule of aging unrealized losses	For those securities in an unrealized loss position, the length of time the securities were in such a position is as follows: Less Than 12 Months 12 Months or Greater Total # of Securities Fair Value Unrealized Losses # of Securities Fair Value Unrealized Losses # of Securities Fair Value Unrealized Losses As of September 30, 2021 (Dollars in Thousands) Municipal debt securities 116 $ 223,105 $ (2,735) — $ — 116 $ 223,105 $ (2,735) Corporate debt securities 94 598,002 (9,258) 4 29,367 (1,220) 98 627,369 (10,478) Asset-backed securities 2 4,228 (28) 1 2,001 (49) 3 6,229 (77) Short-term investments 2 1,649 — — — — 2 1,649 — Total 214 $ 826,984 $ (12,021) 5 $ 31,368 $ (1,269) 219 $ 858,352 $ (13,290) Less Than 12 Months 12 Months or Greater Total # of Securities Fair Value Unrealized Losses # of Securities Fair Value Unrealized Losses # of Securities Fair Value Unrealized Losses As of December 31, 2020 (Dollars in Thousands) Municipal debt securities 4 3,548 (2) — — — 4 3,548 (2) Corporate debt securities 9 40,081 (483) 1 33 — 10 40,114 (483) Asset-backed securities 2 5,191 (19) 1 2,495 (8) 3 7,686 (27) Total 15 $ 48,820 $ (504) 2 $ 2,528 $ (8) 17 $ 51,348 $ (512)
Schedule of components of net investment income	The following table presents the components of net investment income: For the three months ended September 30, For the nine months ended September 30, 2021 2020 2021 2020 (In Thousands) Investment income $ 10,170 $ 8,624 $ 29,003 $ 24,293 Investment expenses (339) (287) (976) (782) Net investment income $ 9,831 $ 8,337 $ 28,027 $ 23,511
Schedule of net realized investment losses	The following table presents the components of net realized investment losses: For the three months ended September 30, For the nine months ended September 30, 2021 2020 2021 2020 (In Thousands) Gross realized investment gains $ 3 $ — $ 15 $ 5,126 Gross realized investment losses — (4) — (4,491) Net realized investment gains (losses) $ 3 $ (4) $ 15 $ 635

Fair Value of Financial Instr_2

Fair Value of Financial Instruments (Tables)	9 Months Ended
	Sep. 30, 2021
Fair Value Disclosures [Abstract]
Schedule of fair value measurements of financial instruments	The following tables present the level within the fair value hierarchy at which our financial instruments were measured: Fair Value Measurements Using Quoted Prices in Significant Other Significant Fair Value As of September 30, 2021 (In Thousands) U.S. Treasury securities and obligations of U.S. government agencies $ 30,819 $ — $ — $ 30,819 Municipal debt securities — 508,994 — 508,994 Corporate debt securities — 1,397,162 — 1,397,162 Asset-backed securities — 106,429 — 106,429 Cash, cash equivalents and short-term investments 108,275 — — 108,275 Total assets $ 139,094 $ 2,012,585 $ — $ 2,151,679 Warrant liability — — 3,010 3,010 Total liabilities $ — $ — $ 3,010 $ 3,010 Fair Value Measurements Using Quoted Prices in Significant Other Significant Fair Value As of December 31, 2020 (In Thousands) U.S. Treasury securities and obligations of U.S. government agencies $ 31,598 $ — $ — $ 31,598 Municipal debt securities — 421,348 — 421,348 Corporate debt securities — 1,219,791 — 1,219,791 Asset-backed securities — 131,180 — 131,180 Cash, cash equivalents and short-term investments 127,306 — — 127,306 Total assets $ 158,904 $ 1,772,319 $ — $ 1,931,223 Warrant liability — — 4,409 4,409 Total liabilities $ — $ — $ 4,409 $ 4,409
Roll-forward of level 3 liabilities measured at fair value	The following table provides a roll-forward of Level 3 liabilities measured at fair value: For the nine months ended September 30, Warrant Liability 2021 2020 (In Thousands) Balance, January 1 $ 4,409 $ 7,641 Change in fair value of warrant liability included in earnings (454) (4,286) Issuance of common stock on warrant exercise (945) (220) Balance, September 30 $ 3,010 $ 3,135
Schedule of key inputs and assumptions in option-pricing model	The following table outlines the key inputs and assumptions used to calculate the fair value of the warrant liability in the Black-Scholes option-pricing model as of the dates indicated. As of September 30, 2021 2020 Common stock price $ 22.61 $ 17.80 Risk free interest rate 0.05 % 0.13 % Expected life 0.56 years 1.56 years Expected volatility 34.4 % 75.3 % Dividend yield 0 % 0 %

Reinsurance (Tables)

Reinsurance (Tables)	9 Months Ended
	Sep. 30, 2021
Reinsurance Disclosures [Abstract]
Schedule of effects of reinsurance	The effect of our reinsurance agreements on premiums written and earned is as follows: For the three months ended For the nine months ended September 30, 2021 September 30, 2020 September 30, 2021 September 30, 2020 (In Thousands) Net premiums written Direct $ 134,635 $ 119,323 $ 419,811 $ 331,254 Ceded (1) (22,704) (17,501) (65,423) (47,952) Net premiums written $ 111,931 $ 101,822 $ 354,388 $ 283,302 Net premiums earned Direct $ 137,159 $ 118,552 $ 399,005 $ 351,889 Ceded (1) (23,565) (19,750) (68,644) (55,426) Net premiums earned $ 113,594 $ 98,802 $ 330,361 $ 296,463 (1) Net of profit commission. The following table shows amounts related to the QSR Transactions: For the three months ended For the nine months ended September 30, 2021 September 30, 2020 September 30, 2021 September 30, 2020 (In Thousands) Ceded risk-in-force $ 7,610,870 $ 5,159,061 $ 7,610,870 $ 5,159,061 Ceded premiums earned (28,366) (24,517) (81,650) (70,738) Ceded claims and claim expenses 840 3,200 3,214 13,401 Ceding commission earned 6,142 4,798 17,265 13,739 Profit commission 15,191 11,034 42,962 28,718
Schedule of ILN transactions	The following table presents the inception date, covered production p eriod, initial and current reinsurance coverage amount, and initial and current first layer retained aggregate loss under each of the ILN Transactions. Current amounts are presented as of September 30, 2021. ( $ values in thousands) Inception Date Covered Production Initial Reinsurance Coverage Current Reinsurance Coverage Initial First Layer Retained Loss Current First Layer Retained Loss (1) 2017 ILN Transaction May 2, 2017 1/1/2013 - 12/31/2016 $211,320 $40,226 $126,793 $121,196 2018 ILN Transaction July 25, 2018 1/1/2017 - 5/31/2018 264,545 158,489 125,312 122,750 2019 ILN Transaction July 30, 2019 6/1/2018 - 6/30/2019 326,905 231,877 123,424 122,697 2020-1 ILN Transaction July 30, 2020 7/1/2019 - 3/31/2020 322,076 84,470 169,514 169,488 2020-2 ILN Transaction October 29, 2020 4/1/2020 - 9/30/2020 (2) 242,351 177,566 121,777 121,177 2021-1 ILN Transaction (4) April 27, 2021 10/1/2020 - 3/31/2021 (3) 367,238 367,238 163,708 163,708 (1) NMIC applies claims paid on covered policies against its first layer aggregate retained loss exposure and cedes reserves for incurred claims and claims expenses to each applicable ILN Transaction and recognizes a reinsurance recoverable if such incurred claims and claims expenses exceed its current first layer retained loss. (2) Approximately 1% of the production covered by the 2020-2 ILN Transaction has coverage reporting dates between July 1, 2019 and March 31, 2020. (3) Approximately 1% of the production covered by the 2021-1 ILN Transaction has coverage reporting dates between July 1, 2019 and September 30, 2020. (4) As of September 30, 2021, the current reinsurance coverage amount on the 2021-1 ILN transaction is equal to the initial reinsurance coverage, as the reinsurance coverage provided by Oaktown Re will not decrease until its target credit enhancement is met.

Reserves for Insurance Claims_2

Reserves for Insurance Claims and Claim Expenses (Tables)	9 Months Ended
	Sep. 30, 2021
Insurance [Abstract]
Reconciliation of liability for insurance claims and claim expenses	The following table provides a reconciliation of the beginning and ending gross reserve balances for primary insurance claims and claim expenses: For the nine months ended September 30, 2021 2020 (In Thousands) Beginning balance $ 90,567 $ 23,752 Less reinsurance recoverables (1) (17,608) (4,939) Beginning balance, net of reinsurance recoverables 72,959 18,813 Add claims incurred: Claims and claim expenses incurred: Current year (2) 19,275 61,198 Prior years (3) (6,469) (5,500) Total claims and claim expenses incurred 12,806 55,698 Less claims paid: Claims and claim expenses paid: Current year (2) 15 152 Prior years (3) 1,566 4,309 Total claims and claim expenses paid 1,581 4,461 Reserve at end of period, net of reinsurance recoverables 84,184 70,050 Add reinsurance recoverables (1) 20,420 17,180 Ending balance $ 104,604 $ 87,230 (1) Related to ceded losses recoverable under the QSR Transactions. See Note 5, " Reinsurance " for additional information. (2) Related to insured loans with their most recent defaults occurring in the current year. For example, if a loan defaulted in a prior year and subsequently cured and later re-defaulted in the current year, the default would be included in the current year. Amounts are presented net of reinsurance and included $14.0 million attributed to net case reserves and $4.8 million attributed to net IBNR reserves for the nine months ended September 30, 2021 and $55.4 million attributed to net case reserves and $4.8 million attributed to net IBNR reserves for the nine months ended September 30, 2020. (3) Related to insured loans with defaults occurring in prior years, which have been continuously in default before the start of the current year. Amounts are presented net of reinsurance and included $1.8 million attributed to net case reserves and $5.0 million attributed to net IBNR reserves for the nine months ended September 30, 2021 and $4.0 million attributed to net case reserves and $1.3 million attributed to net IBNR reserves for the nine months ended September 30, 2020.

Earnings per Share (EPS) (Table

Earnings per Share (EPS) (Tables)	9 Months Ended
	Sep. 30, 2021
Earnings Per Share [Abstract]
Schedule of earnings per share, basic and diluted	For the three months ended September 30, For the nine months ended September 30, 2021 2020 2021 2020 (In Thousands, except for per share data) Net income $ 60,193 $ 38,179 $ 170,606 $ 123,298 Basic weighted average shares outstanding 85,721 84,805 85,563 75,695 Basic earnings per share $ 0.70 $ 0.45 $ 1.99 $ 1.63 Net income $ 60,193 $ 38,179 $ 170,606 $ 123,298 Gain from change in fair value of warrant liability — — (454) (4,286) Diluted net income $ 60,193 $ 38,179 $ 170,152 $ 119,012 Basic weighted average shares outstanding 85,721 84,805 85,563 75,695 Dilutive effect of issuable shares 1,159 794 1,231 1,172 Diluted weighted average shares outstanding 86,880 85,599 86,794 76,867 Diluted earnings per share $ 0.69 $ 0.45 $ 1.96 $ 1.55 Anti-dilutive shares 1 420 2 91

Regulatory Information (Tables)

Regulatory Information (Tables)	9 Months Ended
	Sep. 30, 2021
Insurance [Abstract]
Schedule of statutory net income (loss), surplus, contingency reserve and risk-to-capital ratio	The following table presents NMIC and Re One's combined statutory surplus, contingency reserve, statutory capital and risk-to-capital (RTC) ratio: September 30, 2021 December 31, 2020 (In Thousands) Statutory surplus $ 913,471 $ 894,331 Contingency reserve 967,826 768,324 Statutory capital (1) $ 1,881,297 $ 1,662,655 Risk-to-capital 12.5:1 11.7:1 (1) Represents the total of the statutory surplus and contingency reserve.

Organization, Basis of Presen_3

Organization, Basis of Presentation and Summary of Accounting Principles - Narrative (Details)	Sep. 30, 2021state
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Number of states in which the entity operates	50

Investments - Fair Values and G

Investments - Fair Values and Gross Unrealized Gains and Losses (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	$ 2,024,639	$ 1,730,835
Gross unrealized gains	43,070	73,963
Gross unrealized losses	(13,290)	(512)
Fair Value	2,054,419	1,804,286
U.S. Treasury securities and obligations of U.S. government agencies
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	29,435	29,412
Gross unrealized gains	1,384	2,186
Gross unrealized losses	0	0
Fair Value	30,819	31,598
Municipal debt securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	503,615	407,323
Gross unrealized gains	8,114	14,027
Gross unrealized losses	(2,735)	(2)
Fair Value	508,994	421,348
Corporate debt securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	1,375,589	1,165,260
Gross unrealized gains	32,051	55,014
Gross unrealized losses	(10,478)	(483)
Fair Value	1,397,162	1,219,791
Asset-backed securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	104,990	128,471
Gross unrealized gains	1,516	2,736
Gross unrealized losses	(77)	(27)
Fair Value	106,429	131,180
Total bonds
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	2,013,629	1,730,466
Gross unrealized gains	43,065	73,963
Gross unrealized losses	(13,290)	(512)
Fair Value	2,043,404	1,803,917
Short-term investments
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	11,010	369
Gross unrealized gains	5	0
Gross unrealized losses	0	0
Fair Value	$ 11,015	$ 369

Investments - Narrative (Detail

Investments - Narrative (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Debt Securities, Available-for-sale [Line Items]
Unrealized loss position, accumulated loss	$ 13,290	$ 512
Unrealized loss position, 12 months or greater	1,269	8
U.S. Treasury securities and obligations of U.S. government agencies
Debt Securities, Available-for-sale [Line Items]
Cash and investments held with various state insurance departments	$ 5,600	$ 5,700

Investments - Corporate Debt Se

Investments - Corporate Debt Securities by Industry Group (Details)	Sep. 30, 2021	Dec. 31, 2020
Debt Securities By Industry [Line Items]
Corporate debt securities as component of total (percent)	100.00%	100.00%
Financial
Debt Securities By Industry [Line Items]
Corporate debt securities as component of total (percent)	38.00%	37.00%
Consumer
Debt Securities By Industry [Line Items]
Corporate debt securities as component of total (percent)	23.00%	23.00%
Communications
Debt Securities By Industry [Line Items]
Corporate debt securities as component of total (percent)	12.00%	10.00%
Technology
Debt Securities By Industry [Line Items]
Corporate debt securities as component of total (percent)	10.00%	10.00%
Utilities
Debt Securities By Industry [Line Items]
Corporate debt securities as component of total (percent)	10.00%	11.00%
Industrial
Debt Securities By Industry [Line Items]
Corporate debt securities as component of total (percent)	7.00%	9.00%

Investments - Scheduled Maturit

Investments - Scheduled Maturities (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Amortized Cost
Due in one year or less	$ 66,077	$ 57,429
Due after one through five years	624,658	507,444
Due after five through ten years	1,165,336	1,016,230
Due after ten years	63,578	21,261
Asset-backed securities	104,990	128,471
Amortized Cost	2,024,639	1,730,835
Fair Value
Due in one year or less	66,624	57,949
Due after one through five years	646,757	536,520
Due after five through ten years	1,170,933	1,056,098
Due after ten years	63,676	22,539
Asset-backed securities	106,429	131,180
Fair Value	$ 2,054,419	$ 1,804,286

Investments - Aging of Unrealiz

Investments - Aging of Unrealized Losses (Details) $ in Thousands	Sep. 30, 2021USD ($)security	Dec. 31, 2020USD ($)security
Debt Securities, Available-for-sale [Line Items]
Number of securities, less than 12 months | security	214	15
Fair value, less than 12 months	$ 826,984	$ 48,820
Unrealized losses, less than 12 months	$ (12,021)	$ (504)
Number of securities,12 months or greater | security	5	2
Fair value, 12 months or greater	$ 31,368	$ 2,528
Unrealized losses, 12 months or greater	$ (1,269)	$ (8)
Number of securities, total | security	219	17
Fair Value	$ 858,352	$ 51,348
Unrealized Losses	$ (13,290)	$ (512)
Municipal debt securities
Debt Securities, Available-for-sale [Line Items]
Number of securities, less than 12 months | security	116	4
Fair value, less than 12 months	$ 223,105	$ 3,548
Unrealized losses, less than 12 months	$ (2,735)	$ (2)
Number of securities,12 months or greater | security	0	0
Fair value, 12 months or greater	$ 0	$ 0
Unrealized losses, 12 months or greater		$ 0
Number of securities, total | security	116	4
Fair Value	$ 223,105	$ 3,548
Unrealized Losses	$ (2,735)	$ (2)
Corporate debt securities
Debt Securities, Available-for-sale [Line Items]
Number of securities, less than 12 months | security	94	9
Fair value, less than 12 months	$ 598,002	$ 40,081
Unrealized losses, less than 12 months	$ (9,258)	$ (483)
Number of securities,12 months or greater | security	4	1
Fair value, 12 months or greater	$ 29,367	$ 33
Unrealized losses, 12 months or greater	$ (1,220)	$ 0
Number of securities, total | security	98	10
Fair Value	$ 627,369	$ 40,114
Unrealized Losses	$ (10,478)	$ (483)
Asset-backed securities
Debt Securities, Available-for-sale [Line Items]
Number of securities, less than 12 months | security	2	2
Fair value, less than 12 months	$ 4,228	$ 5,191
Unrealized losses, less than 12 months	$ (28)	$ (19)
Number of securities,12 months or greater | security	1	1
Fair value, 12 months or greater	$ 2,001	$ 2,495
Unrealized losses, 12 months or greater	$ (49)	$ (8)
Number of securities, total | security	3	3
Fair Value	$ 6,229	$ 7,686
Unrealized Losses	$ (77)	$ (27)
Short-term investments
Debt Securities, Available-for-sale [Line Items]
Number of securities, less than 12 months | security	2
Fair value, less than 12 months	$ 1,649
Unrealized losses, less than 12 months	$ 0
Number of securities,12 months or greater | security	0
Fair value, 12 months or greater	$ 0
Unrealized losses, 12 months or greater	$ 0
Number of securities, total | security	2
Fair Value	$ 1,649
Unrealized Losses	$ 0

Investments - Net Investment In

Investments - Net Investment Income (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Investment Income, Net [Abstract]
Investment income	$ 10,170	$ 8,624	$ 29,003	$ 24,293
Investment expenses	(339)	(287)	(976)	(782)
Net investment income	$ 9,831	$ 8,337	$ 28,027	$ 23,511

Investments - Net Realized Inve

Investments - Net Realized Investment Gains (Losses) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Investments, Debt and Equity Securities [Abstract]
Gross realized investment gains	$ 3	$ 0	$ 15	$ 5,126
Gross realized investment losses	0	(4)	0	(4,491)
Net realized investment gains (losses)	$ 3	$ (4)	$ 15	$ 635

Fair Value of Financial Instr_3

Fair Value of Financial Instruments - Assets and Liabilities at Fair Value (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value of securities	$ 2,054,419	$ 1,804,286
U.S. Treasury securities and obligations of U.S. government agencies
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value of securities	30,819	31,598
Municipal debt securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value of securities	508,994	421,348
Corporate debt securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value of securities	1,397,162	1,219,791
Asset-backed securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value of securities	106,429	131,180
Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash, cash equivalents and short-term investments	108,275	127,306
Total assets	2,151,679	1,931,223
Warrant liability	3,010	4,409
Total liabilities	3,010	4,409
Recurring | U.S. Treasury securities and obligations of U.S. government agencies
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value of securities	30,819	31,598
Recurring | Municipal debt securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value of securities	508,994	421,348
Recurring | Corporate debt securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value of securities	1,397,162	1,219,791
Recurring | Asset-backed securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value of securities	106,429	131,180
Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash, cash equivalents and short-term investments	108,275	127,306
Total assets	139,094	158,904
Warrant liability	0	0
Total liabilities	0	0
Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1) | U.S. Treasury securities and obligations of U.S. government agencies
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value of securities	30,819	31,598
Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1) | Municipal debt securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value of securities	0	0
Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1) | Corporate debt securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value of securities	0	0
Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1) | Asset-backed securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value of securities	0	0
Recurring | Significant Other Observable Inputs (Level 2)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash, cash equivalents and short-term investments	0	0
Total assets	2,012,585	1,772,319
Warrant liability	0	0
Total liabilities	0	0
Recurring | Significant Other Observable Inputs (Level 2) | U.S. Treasury securities and obligations of U.S. government agencies
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value of securities	0	0
Recurring | Significant Other Observable Inputs (Level 2) | Municipal debt securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value of securities	508,994	421,348
Recurring | Significant Other Observable Inputs (Level 2) | Corporate debt securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value of securities	1,397,162	1,219,791
Recurring | Significant Other Observable Inputs (Level 2) | Asset-backed securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value of securities	106,429	131,180
Recurring | Significant Unobservable Inputs (Level 3)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash, cash equivalents and short-term investments	0	0
Total assets	0	0
Warrant liability	3,010	4,409
Total liabilities	3,010	4,409
Recurring | Significant Unobservable Inputs (Level 3) | U.S. Treasury securities and obligations of U.S. government agencies
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value of securities	0	0
Recurring | Significant Unobservable Inputs (Level 3) | Municipal debt securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value of securities	0	0
Recurring | Significant Unobservable Inputs (Level 3) | Corporate debt securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value of securities	0	0
Recurring | Significant Unobservable Inputs (Level 3) | Asset-backed securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value of securities	$ 0	$ 0

Fair Value of Financial Instr_4

Fair Value of Financial Instruments - Rollforward of Level 3 Liabilities (Details) - Significant Unobservable Inputs (Level 3) - Warrant liability - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020
Roll-forward of Level 3 liabilities:
Beginning balance	$ 4,409	$ 7,641
Change in fair value of warrant liability included in earnings	(454)	(4,286)
Issuance of common stock on warrant exercise	(945)	(220)
Ending balance	$ 3,010	$ 3,135

Fair Value of Financial Instr_5

Fair Value of Financial Instruments - Valuation Assumptions for Warrant Liabilities (Details) - Significant Unobservable Inputs (Level 3) - Valuation technique, option pricing model	Sep. 30, 2021$ / shares	Sep. 30, 2020$ / shares
Common stock price
Key Inputs and Assumptions, Valuation Techniques
Warrant liability, measurement input	22.61	17.80
Risk free interest rate
Key Inputs and Assumptions, Valuation Techniques
Warrant liability, measurement input	0.0005	0.0013
Expected life
Key Inputs and Assumptions, Valuation Techniques
Warrant liability, expected life	6 months 21 days	1 year 6 months 21 days
Expected volatility
Key Inputs and Assumptions, Valuation Techniques
Warrant liability, measurement input	0.344	0.753
Dividend yield
Key Inputs and Assumptions, Valuation Techniques
Warrant liability, measurement input	0	0

Fair Value of Financial Instr_6

Fair Value of Financial Instruments - Narrative (Details) - Secured Debt - USD ($)	Sep. 30, 2021	Dec. 31, 2020	Jun. 19, 2020	Jan. 19, 2020
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt instrument face amount			$ 400,000,000
Debt	$ 394,300,000	$ 393,300,000
Debt issuance costs	5,700,000	6,700,000	$ 7,400,000
2018 Term loan
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt instrument face amount				$ 150,000,000
Significant Other Observable Inputs (Level 2)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value of long term debt	$ 457,000,000	$ 447,100,000

Debt - Narrative (Details)

Debt - Narrative (Details) - USD ($)	Jun. 19, 2020	Mar. 20, 2020	Mar. 19, 2020	Sep. 30, 2021	Sep. 30, 2021	Sep. 30, 2020	Dec. 31, 2020	Oct. 30, 2020	Jan. 19, 2020
Debt Instrument [Line Items]
Proceeds from senior secured notes					$ 0	$ 400,000,000
Revolving credit facility
Debt Instrument [Line Items]
Commitment fees in interest expense				$ 100,000	300,000
2018 Term loan
Debt Instrument [Line Items]
Loss on extinguishment of debt						$ 2,600,000
Interest payable				9,800,000	9,800,000		$ 2,500,000
2018 Revolving credit facility
Debt Instrument [Line Items]
Debt issuance costs			$ 600,000
2018 Revolving credit facility | Revolving credit facility
Debt Instrument [Line Items]
Credit facility borrowing capacity			$ 85,000,000
Debt instrument term (years)			3 years
2020 Revolving credit facility | Revolving credit facility
Debt Instrument [Line Items]
Credit facility borrowing capacity		$ 100,000,000						$ 110,000,000
Borrowings outstanding				0	$ 0
Commitment fee (in percent)					0.35%
Debt Issuance costs		$ 800,000
Remaining deferred issuance costs, net of accumulated amortization				$ 700,000	$ 700,000
Debt instrument covenant, maximum debt-to-total capitalization ratio					35.00%
2020 Revolving credit facility | Revolving credit facility | Minimum
Debt Instrument [Line Items]
Commitment fee (in percent)		0.175%
2020 Revolving credit facility | Revolving credit facility | Maximum
Debt Instrument [Line Items]
Commitment fee (in percent)		0.525%
2020 Revolving credit facility | Revolving credit facility | Base rate
Debt Instrument [Line Items]
Variable rate floor (in percent)		1.00%
2020 Revolving credit facility | Revolving credit facility | Base rate | Minimum
Debt Instrument [Line Items]
Basis spread on variable rate (in percent)		0.375%
2020 Revolving credit facility | Revolving credit facility | Base rate | Maximum
Debt Instrument [Line Items]
Basis spread on variable rate (in percent)		1.875%
2020 Revolving credit facility | Revolving credit facility | Eurodollar | Minimum
Debt Instrument [Line Items]
Basis spread on variable rate (in percent)		1.375%
2020 Revolving credit facility | Revolving credit facility | Eurodollar | Maximum
Debt Instrument [Line Items]
Basis spread on variable rate (in percent)		2.875%
General corporate purposes
Debt Instrument [Line Items]
Proceeds from senior secured notes	$ 244,400,000
Secured Debt
Debt Instrument [Line Items]
Debt instrument face amount	$ 400,000,000
Stated interest rate (in percent)				7.375%	7.375%
Applicable premium	1.00%
Percent of aggregate balance redeemable with equity offerings	40.00%
Debt issuance costs	$ 7,400,000			$ 5,700,000	$ 5,700,000		$ 6,700,000
Senior secured notes				$ 400,000,000	$ 400,000,000
Secured Debt | 2018 Term loan
Debt Instrument [Line Items]
Debt instrument face amount									$ 150,000,000
Secured Debt | Prior to March 1, 2025
Debt Instrument [Line Items]
Redemption price (in percent)	100.00%
Secured Debt | After March 1, 2025
Debt Instrument [Line Items]
Redemption price (in percent)	100.00%
Secured Debt | Prior to June 1, 2022
Debt Instrument [Line Items]
Redemption price (in percent)	107.375%

Reinsurance - Effect of Reinsur

Reinsurance - Effect of Reinsurance Agreements on Premiums Written and Earned (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Net premiums written
Direct	$ 134,635	$ 119,323	$ 419,811	$ 331,254
Ceded	(22,704)	(17,501)	(65,423)	(47,952)
Net premiums written	111,931	101,822	354,388	283,302
Net premiums earned
Direct	137,159	118,552	399,005	351,889
Ceded	(23,565)	(19,750)	(68,644)	(55,426)
Net premiums earned	$ 113,594	$ 98,802	$ 330,361	$ 296,463

Reinsurance - Narrative (Detail

Reinsurance - Narrative (Details) - USD ($) $ in Thousands	Apr. 01, 2019	Mar. 31, 2019	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020	Dec. 31, 2020	Dec. 31, 2019
Ceded Credit Risk [Line Items]
Restricted cash			$ 3,572		$ 3,572		$ 5,555
Reinsurance recoverable on unpaid claims			$ 20,420	$ 17,180	$ 20,420	$ 17,180	$ 17,608	$ 4,939
ILN transactions
Ceded Credit Risk [Line Items]
Reinsurance coverage amount amortized (as a percent)			10.00%		10.00%
2018 QSR transaction
Ceded Credit Risk [Line Items]
Reinsurance recoverable on unpaid claims			$ 15,600		$ 15,600
2020 QSR transaction
Ceded Credit Risk [Line Items]
Reinsurance recoverable on unpaid claims			15,600		15,600
2021 QSR Transaction
Ceded Credit Risk [Line Items]
Reinsurance recoverable on unpaid claims			15,600		15,600
Third-party reinsurers | 2017 ILN transaction
Ceded Credit Risk [Line Items]
Risk premiums paid			10,400	$ 6,300	$ 30,000	$ 13,400
Third-party reinsurers | QSR transactions
Ceded Credit Risk [Line Items]
Percentage of ceding commission received					20.00%
Third-party reinsurers | Eligible policies, pool one
Ceded Credit Risk [Line Items]
Percent of premiums ceded under QSR Transaction	20.50%	25.00%
Third-party reinsurers | Fannie Mae
Ceded Credit Risk [Line Items]
Percent of premiums ceded under QSR Transaction					100.00%
Third-party reinsurers | Risk written policies in 2018
Ceded Credit Risk [Line Items]
Percent of premiums earned under 2018 QSR Transaction					25.00%
Third-party reinsurers | Risk written policies in 2019
Ceded Credit Risk [Line Items]
Percent of premiums ceded under QSR Transaction					20.00%
Third-party reinsurers | Risk written policies in 2020
Ceded Credit Risk [Line Items]
Percent of premiums earned under 2018 QSR Transaction					21.00%
Third-party reinsurers | Eligible Policies, Pool Seven
Ceded Credit Risk [Line Items]
Percent of premiums earned under 2018 QSR Transaction					22.50%
Third-party reinsurers | 2016 QSR transaction
Ceded Credit Risk [Line Items]
Previously ceded primary RIF recaptured	$ 500,000
Threshold for loss ratio on loans to qualify for profit commission					60.00%
Reinsurance recoverable on unpaid claims			$ 4,800		$ 4,800
Third-party reinsurers | 2018 QSR transaction
Ceded Credit Risk [Line Items]
Threshold for loss ratio on loans to qualify for profit commission					61.00%
Third-party reinsurers | 2020 QSR transaction
Ceded Credit Risk [Line Items]
Threshold for loss ratio on loans to qualify for profit commission					50.00%
Third-party reinsurers | 2021 QSR Transaction
Ceded Credit Risk [Line Items]
Threshold for loss ratio on loans to qualify for profit commission					57.50%
Maximum
Ceded Credit Risk [Line Items]
Reinsurance coverage, term of underlying mortgage amortization (in years)					12 years 6 months
Maximum | Third-party reinsurers | 2017 ILN transaction
Ceded Credit Risk [Line Items]
Anticipated payment related to annual operating expenses					$ 250
Maximum | Third-party reinsurers | 2018 ILN transaction
Ceded Credit Risk [Line Items]
Anticipated payment related to annual operating expenses					$ 300
Minimum
Ceded Credit Risk [Line Items]
Reinsurance coverage, term of underlying mortgage amortization (in years)					10 years

Reinsurance - ILN Transactions

Reinsurance - ILN Transactions (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Apr. 27, 2021	Oct. 29, 2020	Jul. 30, 2020	Jul. 30, 2019	Jul. 25, 2018	May 02, 2017
2017 ILN Transaction
Deferred Compensation Arrangement with Individual, Excluding Share-based Payments and Postretirement Benefits [Line Items]
Initial Reinsurance Coverage							$ 211,320
Current Reinsurance Coverage	$ 40,226
Initial First Layer Retained Loss							$ 126,793
Current first layer retained loss	121,196
2018 ILN Transaction
Deferred Compensation Arrangement with Individual, Excluding Share-based Payments and Postretirement Benefits [Line Items]
Initial Reinsurance Coverage						$ 264,545
Current Reinsurance Coverage	158,489
Initial First Layer Retained Loss						$ 125,312
Current first layer retained loss	122,750
2019 ILN Transaction
Deferred Compensation Arrangement with Individual, Excluding Share-based Payments and Postretirement Benefits [Line Items]
Initial Reinsurance Coverage					$ 326,905
Current Reinsurance Coverage	231,877
Initial First Layer Retained Loss					$ 123,424
Current first layer retained loss	122,697
2020-1 ILN Transaction
Deferred Compensation Arrangement with Individual, Excluding Share-based Payments and Postretirement Benefits [Line Items]
Initial Reinsurance Coverage				$ 322,076
Current Reinsurance Coverage	84,470
Initial First Layer Retained Loss				$ 169,514
Current first layer retained loss	169,488
2020-2 ILN Transaction
Deferred Compensation Arrangement with Individual, Excluding Share-based Payments and Postretirement Benefits [Line Items]
Initial Reinsurance Coverage			$ 242,351
Current Reinsurance Coverage	177,566
Initial First Layer Retained Loss			$ 121,777
Current first layer retained loss	$ 121,177
Percentage of population with production prior to period start date	1.00%
2021-1 ILN Transaction
Deferred Compensation Arrangement with Individual, Excluding Share-based Payments and Postretirement Benefits [Line Items]
Initial Reinsurance Coverage		$ 367,238
Current Reinsurance Coverage	$ 367,238
Initial First Layer Retained Loss		$ 163,708
Current first layer retained loss	$ 163,708
Percentage of population with production prior to period start date	1.00%

Reinsurance - Amounts Related t

Reinsurance - Amounts Related to QSR Transactions (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Ceded Credit Risk [Line Items]
Ceded premiums earned	$ (23,565)	$ (19,750)	$ (68,644)	$ (55,426)
Third-party reinsurers
Ceded Credit Risk [Line Items]
Ceded risk-in-force	7,610,870	5,159,061	7,610,870	5,159,061
Ceded premiums earned	(28,366)	(24,517)	(81,650)	(70,738)
Ceded claims and claim expenses	840	3,200	3,214	13,401
Ceding commission earned	6,142	4,798	17,265	13,739
Profit commission	$ 15,191	$ 11,034	$ 42,962	$ 28,718

Reserves for Insurance Claims_3

Reserves for Insurance Claims and Claim Expenses - Narrative (Details) $ in Thousands	9 Months Ended
	Sep. 30, 2021USD ($)claimloan	Dec. 31, 2020USD ($)	Sep. 30, 2020USD ($)loanpolicy	Dec. 31, 2019USD ($)
Liability for Claims and Claims Adjustment Expense [Line Items]
Primary loans in default | loan	7,670		13,765
Total gross liability for unpaid claims and claim adjustment expenses	$ 104,604	$ 90,567	$ 87,230	$ 23,752
Number of claims paid | claim	59
Claims paid, including amounts covered by insurance	$ 2,000
Default percent (in percent)	1.56%		3.60%
Total number of policies in-force	490,714		381,899
Reserve for prior year insurance claims and claim expenses	$ 80,600
Fannie Mae
Liability for Claims and Claims Adjustment Expense [Line Items]
Number of loans in pool past due 60 days or more | loan	121
Risk-in-Force of loans in pool past due 60 days or more	$ 9,900
Loan-to-value ratio (less than)	0.80
Claims applied to pool deductible	$ 1,000
Deductible on policy	$ 9,400
QSR transactions
Liability for Claims and Claims Adjustment Expense [Line Items]
Number of covered claims included in number of claims paid | claim	57
Component of claims paid covered under QSR Transaction	$ 400
2016 QSR transaction | Fannie Mae
Liability for Claims and Claims Adjustment Expense [Line Items]
Percent of pool RIF reinsured	100.00%

Reserves for Insurance Claims_4

Reserves for Insurance Claims and Claim Expenses - Reconciliation of Reserve Balances for Insurance Claims and Claim Expense (Details) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020
Liability for Unpaid Claims and Claims Adjustment Expense [Roll Forward]
Beginning balance	$ 90,567	$ 23,752
Less reinsurance recoverables	17,608	4,939
Beginning balance, net of reinsurance recoverables	72,959	18,813
Claims and claim expenses incurred:
Current year	19,275	61,198
Prior years	(6,469)	(5,500)
Total claims and claim expenses incurred	12,806	55,698
Claims and claim expenses paid:
Current year	15	152
Prior years	1,566	4,309
Total claims and claim expenses paid	1,581	4,461
Reserve at end of period, net of reinsurance recoverables	84,184	70,050
Add reinsurance recoverables	20,420	17,180
Ending balance	104,604	87,230
Current year case reserves	14,000	55,400
Current year IBNR	4,800	4,800
Prior year case reserves	1,800	4,000
Prior year, IBNR	$ 5,000	$ 1,300

Earnings per Share (EPS) (Detai

Earnings per Share (EPS) (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended						9 Months Ended
	Sep. 30, 2021	Jun. 30, 2021	Mar. 31, 2021	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Sep. 30, 2021	Sep. 30, 2020
Earnings per Share, Basic [Abstract]
Net income	$ 60,193	$ 57,522	$ 52,891	$ 38,179	$ 26,848	$ 58,271	$ 170,606	$ 123,298
Basic weighted average shares outstanding (in shares)	85,721			84,805			85,563	75,695
Basic earnings per share (in dollars per share)	$ 0.70			$ 0.45			$ 1.99	$ 1.63
Earnings per Share, Diluted [Abstract]
Net income	$ 60,193	$ 57,522	$ 52,891	$ 38,179	$ 26,848	$ 58,271	$ 170,606	$ 123,298
Gain from change in fair value of warrant liability	0			0			(454)	(4,286)
Diluted net income	$ 60,193			$ 38,179			$ 170,152	$ 119,012
Basic weighted average shares outstanding (in shares)	85,721			84,805			85,563	75,695
Dilutive effect of issuable shares (in shares)	1,159			794			1,231	1,172
Dilutive weighted average shares outstanding (in shares)	86,880			85,599			86,794	76,867
Diluted earnings per share (in dollars per share)	$ 0.69			$ 0.45			$ 1.96	$ 1.55
Anti-dilutive shares (in shares)	1			420			2	91

Warrants (Details)

Warrants (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020	Dec. 31, 2020	Apr. 30, 2012
Debt Disclosure [Abstract]
Warrants issued (in shares)						992,000
Class of warrant or right, outstanding (in shares)	239,000		239,000
Right to purchase, number of shares per warrant (in shares)						1
Exercise price of warrants (in dollars per warrant)						$ 10
Warrant liability, at fair value	$ 3,010		$ 3,010		$ 4,409	$ 5,100
Warrants exercised (in shares)	32,000	0	73,000	9,000
Stock issued upon exercise of warrants (in shares)	28,000		60,000	6,000
Fair value of warrant liability reclassified to additional paid in capital upon exercise	$ 400		$ 900	$ 200

Income Taxes (Details)

Income Taxes (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020	Dec. 31, 2020
Income Tax Disclosure [Abstract]
Effective income tax rate on pre-tax income or loss	22.30%	22.60%	21.90%	21.20%
Tax and loss bonds	$ 46.4		$ 46.4		$ 46.4

Premium Receivable (Details)

Premium Receivable (Details)	9 Months Ended
	Sep. 30, 2021
Insurance [Abstract]
Number of days to be written off	120 days

Regulatory Information - Narrat

Regulatory Information - Narrative (Details) - NMIC and Re One combined - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020	Dec. 31, 2020
Statutory Accounting Practices [Line Items]
Net income amount	$ 8.7	$ 5.6	$ 23.9	$ 22.6
Aggregate dividend capacity					$ 1.6

Regulatory Information - Schedu

Regulatory Information - Schedule of Combined Statutory Net Loss, Statutory Surplus, Contingency Reserve and RTC Ratios (Details) - NMIC and Re One combined $ in Thousands	Sep. 30, 2021USD ($)	Dec. 31, 2020USD ($)
Statutory Accounting Practices [Line Items]
Statutory surplus	$ 913,471	$ 894,331
Contingency reserve	967,826	768,324
Statutory capital	$ 1,881,297	$ 1,662,655
Risk to capital ratio regulatory actual	12.5	11.7

Subsequent Event (Details)

Subsequent Event (Details) - Subsequent Event - USD ($) $ in Thousands	Oct. 27, 2021	Oct. 31, 2021
Subsequent Event [Line Items]
Amount retained	$ 146,200
Third-party reinsurers | 2022 and 2023 QSR Transaction
Subsequent Event [Line Items]
Percent of premiums earned under 2018 QSR Transaction		20.00%
Percentage of ceding commission received		20.00%
Threshold for loss ratio on loans to qualify for profit commission		62.00%
Oaktown Re VII Ltd. | Mortgage insurance-linked notes
Subsequent Event [Line Items]
Debt instrument face amount	363,600
Maximum
Subsequent Event [Line Items]
Annual risk premium payments, capped amount	250
Oaktown Re VII Ltd. | Maximum
Subsequent Event [Line Items]
Amount reinsured	$ 363,600