NMI (NMIH) 10-Q 2 May 19 2019 Q1 Quarterly report Financial data

Document and Entity Information

Document and Entity Information - shares	3 Months Ended
	Mar. 31, 2019	Apr. 26, 2019
Document and Entity Information [Abstract]
Entity Registrant Name	NMI HOLDINGS, INC.
Entity Central Index Key	0001547903
Document Type	10-Q
Document Period End Date	Mar. 31, 2019
Amendment Flag	false
Entity Filer Category	Large Accelerated Filer
Entity Emerging Growth Company	false
Entity Small Business	false
Document Fiscal Year Focus	2019
Document Fiscal Period Focus	Q1
Current Fiscal Year End Date	--12-31
Entity Common Stock, Shares Outstanding		67,533,958

CONDENSED CONSOLIDATED BALANCE

CONDENSED CONSOLIDATED BALANCE SHEETS (UNAUDITED) - USD ($) $ in Thousands		Mar. 31, 2019	Dec. 31, 2018
Assets
Fixed maturities, available-for-sale, at fair value (amortized cost of $934,712 and $924,987 as of March 31, 2019 and December 31, 2018, respectively)		$ 940,223	$ 911,490
Cash and cash equivalents (including restricted cash of $1,422 and $1,414 as of March 31, 2019 and December 31, 2018, respectively)		39,761	25,294
Premiums receivable		38,478	36,007
Accrued investment income		6,553	5,694
Prepaid expenses		4,454	3,241
Deferred policy acquisition costs, net		48,820	46,840
Software and equipment, net		25,105	24,765
Intangible assets and goodwill		3,634	3,634
Prepaid reinsurance premiums		27,747	30,370
Other assets		12,736	4,708
Total assets		1,147,511	1,092,043
Liabilities
Term loan		146,503	146,757
Unearned premiums		154,325	158,893
Accounts payable and accrued expenses		16,981	31,141
Reserve for insurance claims and claim expenses		15,537	12,811
Reinsurance funds withheld		25,308	27,114
Warrant liability, at fair value		11,831	7,296
Deferred tax liability, net		12,770	2,740
Other liabilities	[1]	12,375	3,791
Total liabilities		395,630	390,543
Commitments and contingencies
Shareholders' equity
Common stock - class A shares, $0.01 par value; 67,501,958 and 66,318,849 shares issued and outstanding as of March 31, 2019 and December 31, 2018, respectively (250,000,000 shares authorized)		675	663
Additional paid-in capital		684,635	682,181
Accumulated other comprehensive income (loss), net of tax		184	(14,832)
Retain earnings		66,387	33,488
Total shareholders' equity		751,881	701,500
Total liabilities and shareholders' equity		$ 1,147,511	$ 1,092,043
[1]	Deferred Ceding Commissions have been reclassified to "Other Liabilities" in prior periods

CONDENSED CONSOLIDATED BALANC_2

CONDENSED CONSOLIDATED BALANCE SHEETS (UNAUDITED) (Parenthetical) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Statement of Financial Position [Abstract]
Fixed maturities, available-for-sale, amortized cost	$ 934,712	$ 924,987
Restricted cash	$ 1,422	$ 1,414
Common stock, par value (in dollars per share)	$ 0.01	$ 0.01
Common stock, issued (in shares)	67,501,958	66,318,849
Common stock, outstanding (in shares)	67,501,958	66,318,849
Common stock, authorized (in shares)	250,000,000	250,000,000

CONDENSED CONSOLIDATED STATEMEN

CONDENSED CONSOLIDATED STATEMENTS OF OPERATIONS AND COMPREHENSIVE INCOME (LOSS) (UNAUDITED) - USD ($) shares in Thousands, $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Revenues
Net premiums earned	$ 73,868	$ 54,914
Net investment income	7,383	4,574
Net realized investment losses	(187)	0
Other revenues	42	64
Total revenues	81,106	59,552
Expenses
Insurance claims and claim expenses	2,743	1,569
Underwriting and operating expenses	30,849	28,453
Total expenses	33,592	30,022
Other expense
Gain (loss) from change in fair value of warrant liability	(5,479)	420
Interest expense	(3,061)	(3,419)
Total other expense	(8,540)	(2,999)
Income before income taxes	38,974	26,531
Income tax expense	6,075	4,176
Net income	$ 32,899	$ 22,355
Earnings per share
Basic earnings per share (in dollars per share)	$ 0.49	$ 0.36
Diluted earnings per share (in dollars per share)	$ 0.48	$ 0.34
Weighted average common shares outstanding
Basic weighted average shares outstanding (in shares)	66,692	62,099
Dilutive weighted average shares outstanding (in shares)	68,996	65,697
Comprehensive income:
Net income	$ 32,899	$ 22,355
Other comprehensive income (loss), net of tax:
Unrealized (losses) gains in accumulated other comprehensive income, net of tax (benefit) expense of $3,953 and ($423) for the quarters ended March 31, 2019 and 2018, respectively	14,868	(10,956)
Reclassification adjustment for realized losses (gains) included in net income, net of tax expense (benefit) of ($39) and $0 for the quarters ended March 31, 2019 and 2018, respectively	148	0
Other comprehensive income (loss), net of tax	15,016	(10,956)
Comprehensive income	$ 47,915	$ 11,399

CONDENSED CONSOLIDATED STATEM_2

CONDENSED CONSOLIDATED STATEMENTS OF OPERATIONS AND COMPREHENSIVE INCOME (LOSS) (UNAUDITED) (Parenthetical) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Income Statement [Abstract]
Net unrealized (losses) gains in accumulated other comprehensive income, tax (benefit) expense	$ 3,953	$ (423)
Reclassification adjustment for realized losses included in net income, tax expense	$ (39)	$ 0

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 (Loss)	Retained Earnings (Accumulated Deficit)
Beginning balance at Dec. 31, 2017		$ 509,077	$ 605		$ 585,488	$ (2,859)	$ (74,157)
Beginning balance (in shares) at Dec. 31, 2017			60,518,000
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Common stock: class A shares issued related to public offering		79,165	$ 43		79,122
Common stock: class A shares issued related to public offering (in shares)			4,255,000
Common stock: class A shares issued related to warrants	[1]	$ 489			489
Common stock: class A shares issued related to warrants (in shares)		25,686	26,000	[1]
Common stock: class A shares issued under stock plans, net of shares withheld for employee taxes		$ (991)	$ 8		(999)
Common stock: class A shares issued under stock plans, net of shares withheld for employee taxes (in shares)			770,000
Share-based compensation expense		2,805			2,805
Change in unrealized investment gains/losses, net of tax		(10,956)				(10,956)
Net income		22,355					22,355
Ending balance at Mar. 31, 2018		601,944	$ 656		666,905	(13,533)	(52,084)
Ending balance (in shares) at Mar. 31, 2018			65,569,000
Beginning balance at Dec. 31, 2018		701,500	$ 663		682,181	(14,832)	33,488
Beginning balance (in shares) at Dec. 31, 2018			66,319,000
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Common stock: class A shares issued related to warrants	[1]	$ 944			944
Common stock: class A shares issued related to warrants (in shares)		39,195	39,000	[1]
Common stock: class A shares issued under stock plans, net of shares withheld for employee taxes		$ (1,459)	$ 12		(1,471)
Common stock: class A shares issued under stock plans, net of shares withheld for employee taxes (in shares)			1,144,000
Share-based compensation expense		2,981			2,981
Change in unrealized investment gains/losses, net of tax		15,016				15,016
Net income		32,899					32,899
Ending balance at Mar. 31, 2019		$ 751,881	$ 675		$ 684,635	$ 184	$ 66,387
Ending balance (in shares) at Mar. 31, 2019			67,502,000
[1]	During the three months ended March 31, 2019 and 2018, we issued 39,195 and 25,686 common shares, respectively, with a par value of $0.01 related to the exercise of warrants, which is 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
	Mar. 31, 2019	Mar. 31, 2018
Statement of Stockholders' Equity [Abstract]
Change in unrealized investment gains/losses, tax expense (benefit)	$ 3,992	$ (423)
Stock issued upon exercise of warrants (in shares)	39,195	25,686
Common stock, par value (in dollars per share)	$ 0.01	$ 0.01

CONDENSED CONSOLIDATED STATEM_5

CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS (UNAUDITED) - USD ($) $ in Thousands		3 Months Ended
		Mar. 31, 2019	Mar. 31, 2018
Cash flows from operating activities
Net income		$ 32,899	$ 22,355
Adjustments to reconcile net income to net cash provided by (used in) operating activities:
Net realized investment losses		187	0
Loss (gain) from change in fair value of warrant liability		5,479	(420)
Depreciation and amortization		2,103	1,858
Net amortization of premium on investment securities		314	439
Amortization of debt discount and debt issuance costs		248	361
Share-based compensation expense		2,981	2,805
Deferred income taxes		6,038	4,009
Changes in operating assets and liabilities:
Premiums receivable		(2,472)	(2,985)
Accrued investment income		(859)	(553)
Prepaid expenses		(1,407)	(1,451)
Deferred policy acquisition costs, net		(1,980)	(2,101)
Other assets	[1]	191	163
Unearned premiums		(4,568)	2,424
Reserve for insurance claims and claim expenses		2,726	1,630
Reinsurance balances, net	[1]	(148)	153
Accounts payable and accrued expenses		(13,453)	(7,556)
Net cash provided by operating activities		28,279	21,131
Cash flows from investing activities
Purchase of short-term investments		(47,994)	(16,858)
Purchase of fixed-maturity investments, available-for-sale		(72,586)	(74,095)
Proceeds from maturity of short-term investments		81,311	31,309
Proceeds from redemptions, maturities and sale of fixed-maturity investments, available-for-sale		29,043	44,444
Additions to software and equipment		(1,751)	(1,370)
Net cash used in investing activities		(11,977)	(16,570)
Cash flows from financing activities
Proceeds from issuance of common stock related to public offering, net of issuance costs		0	79,249
Proceeds from issuance of common stock related to employee equity plans		11,017	4,782
Taxes paid related to net share settlement of equity awards		(12,477)	(5,523)
Repayments of term loan		(375)	(375)
Net cash (used in) provided by financing activities		(1,835)	78,133
Net decrease in cash, cash equivalents and restricted cash		14,467	82,694
Cash, cash equivalents and restricted cash, beginning of period		25,294	19,196
Cash, cash equivalents and restricted cash, end of period		39,761	101,890
Supplemental disclosures of cash flow information
Interest paid		2,617	3,072
Income tax refunded		$ 209	$ 0
[1]	Ceded losses recoverable under our quota-share reinsurance transactions were reclassified from "Other Assets" in prior periods to "Reinsurance balance, net".

Organization, Basis of Presenta

Organization, Basis of Presentation and Summary of Accounting Principles	3 Months Ended
	Mar. 31, 2019
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." In April 2013, NMIC, our primary insurance subsidiary, issued its first mortgage insurance policy. NMIC is licensed to write mortgage insurance in all 50 states and D.C. 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, 2018 , included in our 2018 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. Certain reclassifications to our previously reported financial information have been made to conform to current period presentation. 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, 2019 . 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 2018 10-K, other than as noted in " Recent Accounting Pronouncements - Adopted " below. Recent Accounting Pronouncements - Adopted In February 2016, the Financial Accounting Standards Board (FASB) issued Accounting Standards Update (ASU) 2016-02, Leases (Topic 842). This update requires that businesses recognize rights and obligations associated with certain leases as assets and liabilities on the balance sheet. The standard also requires additional disclosures regarding the amount, timing, and uncertainty of cash flows arising from leases. We adopted this ASU on January 1, 2019 using the modified-retrospective method and applied it prospectively as of the effective date, without adjusting comparative periods presented as permitted by ASU 2018-11, Leases (Topic 842), Targeted Improvements . Adoption of this new standard increased our assets and liabilities by $7.6 million in connection with the recognition of right-of-use assets and lease liabilities, primarily related to the operating lease on our corporate headquarters. Adoption of this standard did not impact our consolidated statements of operations or cash flows. See Note 10, " Leases " for additional information related to our leases. In July 2017, the FASB issued ASU 2017-11, Earnings Per Share (Topic 260), Distinguishing Liabilities from Equity (Topic 480), and Derivatives and Hedging (Topic 815). This update is intended to simplify the accounting for certain equity-linked financial instruments. We adopted this ASU on January 1, 2019. Adoption of this standard had no impact on our consolidated financial statements. In June 2018, the FASB issued ASU 2018-07, Compensation-Stock Compensation (Topic 718). This update expands the scope of Topic 718 to include share-based payments made to non-employees in connection with the acquisition of goods and services. We adopted this ASU on January 1, 2019. Adoption of this standard had no impact on our financial results at this time as we have not made any share-based grants to non-employees as defined in ASC 718-10-20. Recent Accounting Pronouncements - Not Yet Adopted In June 2016, the FASB issued ASU 2016-13, Financial Instruments-Credit Losses (Topic 326). This update requires companies to measure all expected credit losses for financial assets held at the reporting date. The standard also amends the accounting for credit losses on available-for-sale debt securities and purchased financial assets with credit deterioration. The standard will take effect for public business entities for fiscal years, and interim periods within those fiscal years, beginning after December 15, 2019. We are currently reviewing the impact the adoption of this ASU will have, if any, on our financial assets. We do not expect it to impact our accounting for insurance claims and claim expenses as these items are not in the scope of this ASU. In August 2018, the FASB issued ASU 2018-12, Targeted Improvements to the Accounting for Long-Duration Contracts . This update provides guidance to the existing recognition, measurement, presentation and disclosure requirements for long-duration contracts issued by an insurance entity. The standard will take effect for public business entities for fiscal years, and interim periods within those fiscal years, beginning after December 15, 2020. We are currently evaluating the impact the adoption of this ASU will have, if any, on our consolidated financial statements. In August 2018, the FASB issued ASU 2018-13, Fair Value Measurement (Topic 820). This update modifies the fair value measurement disclosure requirements of ASC 820. The standard will take effect for public business entities for fiscal years, and interim periods within those fiscal years, beginning after December 15, 2019. We are currently evaluating the impact the adoption of this ASU will have, if any, on our fair value of financial instruments disclosures. In August 2018, the FASB issued ASU 2018-15, Intangibles - Goodwill and Other - Internal-Use Software (Subtopic 350-40). This update applies to cloud computing arrangements hosted by a vendor and provides companies with guidance on the criteria for capitalizing implementation, set-up and other up-front costs incurred in association with these arrangements. The standard will take effect for public business entities for fiscal years, and interim periods within those fiscal years, beginning after December 15, 2019. We are currently evaluating the impact the adoption of this ASU will have, if any, on our consolidated financial statements.

Investments

Investments	3 Months Ended
	Mar. 31, 2019
Investments, Debt and Equity Securities [Abstract]
Investments	Investments We have designated our investment portfolio as available-for-sale and report it at fair value. The related unrealized gains and losses are, after considering the related tax expense or benefit, recognized through comprehensive income and loss, and on an accumulated basis in shareholders' equity. Net realized investment gains and losses are reported in earnings based on specific identification of securities sold or other-than-temporarily impaired. Fair Values and Gross Unrealized Gains and Losses on Investments Amortized Gross Unrealized Fair Gains Losses As of March 31, 2019 (In Thousands) U.S. Treasury securities and obligations of U.S. government agencies $ 48,189 $ 86 $ (696 ) $ 47,579 Municipal debt securities 91,833 671 (331 ) 92,173 Corporate debt securities 613,016 7,471 (2,871 ) 617,616 Asset-backed securities 156,258 1,241 (125 ) 157,374 Total bonds 909,296 9,469 (4,023 ) 914,742 Short-term investments 25,416 65 — 25,481 Total investments $ 934,712 $ 9,534 $ (4,023 ) $ 940,223 Amortized Gross Unrealized Fair Gains Losses As of December 31, 2018 (In Thousands) U.S. Treasury securities and obligations of U.S. government agencies $ 48,171 $ 35 $ (1,376 ) $ 46,830 Municipal debt securities 92,014 206 (963 ) 91,257 Corporate debt securities 554,079 847 (11,688 ) 543,238 Asset-backed securities 171,990 792 (1,457 ) 171,325 Total bonds 866,254 1,880 (15,484 ) 852,650 Short-term investments 58,733 107 — 58,840 Total investments $ 924,987 $ 1,987 $ (15,484 ) $ 911,490 We did not own any mortgage-backed securities in our asset-backed securities portfolio as March 31, 2019 and December 31, 2018 . The following table presents a breakdown of the fair value of our corporate debt securities by issuer industry group as of March 31, 2019 and December 31, 2018 : March 31, 2019 December 31, 2018 Financial 38 % 38 % Consumer 26 27 Communications 11 12 Utilities 10 7 Industrial 7 7 Technology 5 6 Energy 2 2 Other 1 1 Total 100 % 100 % As of March 31, 2019 and December 31, 2018 , approximately $5.4 million and $5.3 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 values of available-for-sale securities as of March 31, 2019 and December 31, 2018 , 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 March 31, 2019 Amortized Fair (In Thousands) Due in one year or less $ 47,004 $ 46,989 Due after one through five years 399,669 400,793 Due after five through ten years 314,593 317,471 Due after ten years 17,188 17,596 Asset-backed securities 156,258 157,374 Total investments $ 934,712 $ 940,223 As of December 31, 2018 Amortized Fair (In Thousands) Due in one year or less $ 76,087 $ 76,104 Due after one through five years 352,282 347,701 Due after five through ten years 318,728 310,633 Due after ten years 5,900 5,727 Asset-backed securities 171,990 171,325 Total investments $ 924,987 $ 911,490 Aging of Unrealized Losses As of March 31, 2019 , the investment portfolio had gross unrealized losses of $4.0 million , $3.6 million of which has been in an unrealized loss position for a period of 12 months or greater. We did not consider these securities to be other-than-temporarily impaired as of March 31, 2019 . We based our conclusion that these investments were not other-than-temporarily impaired as of March 31, 2019 on the following facts: (i) the unrealized losses were primarily caused by interest rate movements and market fluctuations in credit spreads since the purchase date; (ii) we do not intend to sell these investments; and (iii) we do not believe that it is more likely than not that we will be required to sell these investments before recovery of our amortized cost basis, which may not occur until maturity. 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 March 31, 2019 (Dollars in Thousands) U.S. Treasury securities and obligations of U.S. government agencies — $ — $ — 17 $ 37,425 $ (696 ) 17 $ 37,425 $ (696 ) Municipal debt securities (1) 1 2,000 — 19 33,034 (331 ) 20 35,034 (331 ) Corporate debt securities 23 43,094 (423 ) 89 158,174 (2,448 ) 112 201,268 (2,871 ) Asset-backed securities 10 18,173 (46 ) 20 28,453 (79 ) 30 46,626 (125 ) Short-term investments (1) 1 994 — — — — 1 994 — Total 35 $ 64,261 $ (469 ) 145 $ 257,086 $ (3,554 ) 180 $ 321,347 $ (4,023 ) (1) Includes securities with unrealized losses of less than 12 months which are not identifiable in the schedule due to rounding. 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, 2018 (Dollars in Thousands) U.S. Treasury securities and obligations of U.S. government agencies — $ — $ — 19 $ 41,817 $ (1,376 ) 19 $ 41,817 $ (1,376 ) Municipal debt securities 4 7,409 (11 ) 31 58,658 (952 ) 35 66,067 (963 ) Corporate debt securities 118 226,477 (3,952 ) 126 221,675 (7,736 ) 244 448,152 (11,688 ) Asset-backed securities 25 36,017 (1,136 ) 22 33,988 (321 ) 47 70,005 (1,457 ) Total 147 $ 269,903 $ (5,099 ) 198 $ 356,138 $ (10,385 ) 345 $ 626,041 $ (15,484 ) Net Investment Income The following table presents the components of net investment income: For the three months ended March 31, 2019 2018 (In Thousands) Investment income $ 7,496 $ 4,782 Investment expenses (113 ) (208 ) Net investment income $ 7,383 $ 4,574 The following table presents the components of net realized investment losses: For the three months ended March 31, 2019 2018 (In Thousands) Gross realized investment gains $ 195 $ — Gross realized investment losses (382 ) — Net realized investment losses $ (187 ) $ — Investment Securities - Other-than-Temporary Impairment (OTTI) For the three months ended March 31, 2019 , we recognized a $0.4 million OTTI loss in earnings related to the planned sale of a security in a loss position in April 2019. For the three months ended March 31, 2018 , we did not recognize any OTTI losses. There were no credit losses recognized in earnings for which a portion of an OTTI loss was recognized in accumulated other comprehensive income (loss) for the three months ended March 31, 2019 or 2018 .

Fair Value of Financial Instrum

Fair Value of Financial Instruments	3 Months Ended
	Mar. 31, 2019
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 March 31, 2019 (In Thousands) U.S. Treasury securities and obligations of U.S. government agencies $ 47,579 $ — $ — $ 47,579 Municipal debt securities — 92,173 — 92,173 Corporate debt securities — 617,616 — 617,616 Asset-backed securities — 157,374 — 157,374 Cash, cash equivalents and short-term investments 65,242 — — 65,242 Total assets $ 112,821 $ 867,163 $ — $ 979,984 Warrant liability — — 11,831 11,831 Total liabilities $ — $ — $ 11,831 $ 11,831 Fair Value Measurements Using Quoted Prices in Significant Other Significant Fair Value As of December 31, 2018 (In Thousands) U.S. Treasury securities and obligations of U.S. government agencies $ 46,830 $ — $ — $ 46,830 Municipal debt securities — 91,257 — 91,257 Corporate debt securities — 543,238 — 543,238 Asset-backed securities — 171,325 — 171,325 Cash, cash equivalents and short-term investments 84,134 — — 84,134 Total assets $ 130,964 $ 805,820 $ — $ 936,784 Warrant liability — — 7,296 7,296 Total liabilities $ — $ — $ 7,296 $ 7,296 There were no transfers between Level 1 and Level 2, nor any transfers in or out of Level 3, of the fair value hierarchy during the three months ended March 31, 2019 and the year ended December 31, 2018 . The following is a roll-forward of Level 3 liabilities measured at fair value: For the three months ended March 31, Warrant Liability 2019 2018 (In Thousands) Balance, January 1 $ 7,296 $ 7,472 Change in fair value of warrant liability included in earnings 5,479 (420 ) Issuance of common stock on warrant exercise (944 ) (489 ) Balance, March 31 $ 11,831 $ 6,563 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 March 31, 2019 2018 Common stock price $ 25.87 $ 16.55 Risk free interest rate 2.21 - 2.31% 2.37 % Expected life 1.67 - 3.06 years 2.59 years Expected volatility 42.30 - 45.7% 30.1 % Dividend yield 0% 0% The changes in fair value of the warrant liability for the three months ended March 31, 2019 and 2018 are primarily attributable to changes in the price of our common stock during the respective periods, with additional impact related to changes in the Black-Scholes model inputs and exercises of outstanding warrants.

Debt

Debt	3 Months Ended
	Mar. 31, 2019
Debt Disclosure [Abstract]
Debt	Debt On May 24, 2018, we entered into a credit agreement (2018 Credit Agreement), which provides for (i) a $150 million 5-year senior secured term loan facility (2018 Term Loan) that matures on May 24, 2023; and (ii) a $85 million three-year secured revolving credit facility (2018 Revolving Credit Facility) that matures on May 24, 2021. Proceeds from the 2018 Term Loan were used to repay in full the outstanding amount due under our $150 million amended term loan (2015 Term Loan) due on November 10, 2019, and to pay fees and expenses incurred in connection with the 2018 Credit Agreement. 2018 Term Loan The 2018 Term Loan bears interest at the Eurodollar Rate, as defined in the 2018 Credit Agreement and subject to a 1.00% floor, plus an annual margin rate of 4.75% , representing an all-in rate of 7.25% as of March 31, 2019 , payable monthly based on our current interest period election. Quarterly principal payments of $375 thousand are also required. As of March 31, 2019 , the outstanding principal balance of the 2018 Term Loan was $148.9 million . Interest expense for the 2018 Term Loan includes interest and the amortization of issuance costs, an original issue discount and capitalized modification costs related to the 2015 Term Loan. For the three months ended March 31, 2019 , interest expense was $2.8 million . Remaining unamortized issuance costs were $2.4 million as of March 31, 2019 and are being amortized to interest expense using the effective interest method over the contractual life of the 2018 Term Loan. We are subject to certain covenants under the 2018 Term Loan (as defined in the 2018 Credit Agreement), including (but not limited to) a maximum debt-to-total capitalization ratio (as defined in the 2018 Credit Agreement) of 35% under the 2018 Term Loan. We were in compliance with all covenants as of March 31, 2019 . Future principal payments due under the 2018 Term Loan as of March 31, 2019 are as follows: As of March 31, 2019 Principal (In thousands) 2019 $ 1,125 2020 1,500 2021 1,500 2022 1,500 2023 143,250 Total $ 148,875 2018 Revolving Credit Facility Borrowings under the 2018 Revolving Credit Facility may be used for general corporate purposes and will accrue interest at a variable rate equal to, at our discretion, (i) a base rate (as defined in the 2018 Credit Agreement, subject to a floor of 1.00% per annum) plus a margin of 1.00% to 2.50% per annum, based on the applicable corporate credit rating at the time, or (ii) the Eurodollar Rate (subject to a floor of 0.00% per annum) plus a margin of 2.00% to 3.50% per annum, based on the applicable corporate credit rating at the time. As of March 31, 2019 , no borrowings had been made under the 2018 Revolving Credit Facility. We are required to pay a quarterly commitment fee on the average daily undrawn amount of the 2018 Revolving Credit Facility, which ranges from 0.30% to 0.60% , based on the applicable corporate credit rating at the time. As of March 31, 2019 , the applicable commitment fee was 0.50% . For the three months ended March 31, 2019 , we recorded $0.1 million of commitment fees in interest expense. We incurred issuance costs of $1.5 million in connection with the establishment of the 2018 Revolving Credit Facility, which were deferred and recorded within Other Assets. These costs are being amortized through interest expense over the three-year life of the 2018 Revolving Credit Facility on a straight line basis. For the three months ended March 31, 2019 , we recognized $0.1 million of interest expense from the amortization of deferred issuance costs. At March 31, 2019 , remaining deferred issuance costs were $1.1 million , net of accumulated amortization. We are subject to certain covenants under the 2018 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 as of March 31, 2019 .

Reinsurance

Reinsurance	3 Months Ended
	Mar. 31, 2019
Reinsurance Disclosures [Abstract]
Reinsurance	Reinsurance We enter into third-party reinsurance transactions to actively manage our risk, ensure PMIERs compliance and support the growth of our business. The GSEs and the Wisconsin Office of the Commissioner of Insurance (Wisconsin OCI) have approved 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 March 31, 2019 March 31, 2018 (In Thousands) Net premiums written Direct $ 81,730 $ 66,027 Ceded (1) (9,807 ) (6,997 ) Net premiums written $ 71,923 $ 59,030 Net premiums earned Direct $ 86,298 $ 63,604 Ceded (1) (12,430 ) (8,690 ) Net premiums earned $ 73,868 $ 54,914 (1) Net of profit commission Excess-of-loss reinsurance 2017 ILN Transaction In May 2017, NMIC entered into a reinsurance agreement with Oaktown Re Ltd. (Oaktown Re), which provides for up to $211.3 million of aggregate excess-of-loss reinsurance coverage at inception for new delinquencies on an existing portfolio of mortgage insurance policies written from 2013 through December 31, 2016. For the reinsurance coverage period, NMIC retains the first layer of $126.8 million of aggregate losses, of which $124.7 million remained at March 31, 2019 , and Oaktown Re then provides second layer coverage up to the outstanding reinsurance coverage amount. NMIC then retains losses in excess of the outstanding reinsurance coverage amount. The outstanding reinsurance coverage amount decreases from $211.3 million at inception over a ten -year period as the underlying covered mortgages are amortized or repaid, and/or the mortgage insurance coverage is canceled and was $117.4 million as of March 31, 2019 . The outstanding reinsurance coverage amount will stop amortizing if certain credit enhancement or delinquency thresholds are triggered. Oaktown Re financed the coverage by issuing mortgage insurance-linked notes in an aggregate amount of $211.3 million to unaffiliated investors (the 2017 Notes). The 2017 Notes mature on April 26, 2027. All of the proceeds paid to Oaktown Re from the sale of the 2017 Notes were deposited into a reinsurance trust to collateralize and fund the obligations of Oaktown Re 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 collectively to NMIC's reinsurance agreement with Oaktown Re and the issuance of the 2017 Notes by Oaktown Re as the 2017 ILN Transaction. Under the terms of the 2017 ILN Transaction, NMIC makes risk premium payments for the applicable outstanding reinsurance coverage amount and pays Oaktown Re for anticipated operating expenses (capped at $300 thousand per year). For the three months ended March 31, 2019 and 2018 , NMIC ceded risk premiums of $1.4 million and $1.6 million , respectively. NMIC did not cede any losses to Oaktown Re during the three months ended March 31, 2019 and 2018 . 2018 ILN Transaction In July 2018, NMIC entered into a reinsurance agreement with Oaktown Re II Ltd. (Oaktown Re II), which provides for up to $264.5 million of aggregate excess-of-loss reinsurance coverage at inception for new delinquencies on an existing portfolio of mortgage insurance policies written between January 1, 2017 and May 31, 2018. For the reinsurance coverage period, NMIC retains the first layer of $125.3 million of aggregate losses, of which $125.3 million remained at March 31, 2019 , and Oaktown Re II then provides second layer coverage up to the outstanding reinsurance coverage amount. NMIC then retains losses in excess of the outstanding reinsurance coverage amount. The outstanding reinsurance coverage amount decreases from $264.5 million at inception over a ten-year period as the underlying covered mortgages are amortized or repaid, and/or the mortgage insurance coverage is canceled, and was $264.5 million as of March 31, 2019 . The outstanding reinsurance coverage amount will begin amortizing after an initial period in which a target level of credit enhancement is obtained and will stop amortizing if certain credit enhancement or delinquency thresholds are triggered. Oaktown Re II financed the coverage by issuing mortgage insurance-linked notes in an aggregate amount of $264.5 million to unaffiliated investors (the 2018 Notes). The 2018 Notes mature on July 25, 2028. All of the proceeds paid to Oaktown Re II from the sale of the 2018 Notes were deposited into a reinsurance trust to collateralize and fund the obligations of Oaktown Re II 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 collectively to NMIC's reinsurance agreement with Oaktown Re II and the issuance of the 2018 Notes by Oaktown Re II as the 2018 ILN Transaction. Under the terms of the 2018 ILN Transaction, NMIC makes risk premium payments for the applicable outstanding reinsurance coverage amount and pays Oaktown Re II for anticipated operating expenses (capped at $250 thousand per year). For the three months ended March 31, 2019 , NMIC ceded risk premiums of $1.7 million and did not cede any losses to Oaktown Re II. Under the terms of the 2018 ILN Transaction, we are required to maintain a certain level of restricted funds in a premium deposit account with Bank of New York Mellon until the 2018 Notes have been redeemed in full. "Cash and cash equivalents" on our balance sheet includes restricted cash of $1.4 million as of March 31, 2019 . We are not required to deposit additional funds into the premium deposit account and the restricted balance will decrease over time as the principal balance of the 2018 Notes declines. We refer collectively to the 2017 ILN Transaction and 2018 ILN Transaction as the ILN Transactions. NMIC holds optional termination rights under each ILN Transaction in the event of certain occurrences, including, among others, 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. At inception of each ILN Transaction, we determined that Oaktown Re and Oaktown Re II were variable interest entities (VIEs). However, we concluded that we are not the primary beneficiary of either Oaktown Re or Oaktown Re II because NMIC does not have significant economic exposure to either Oaktown Re or Oaktown Re II, and, as such, we do not consolidate the VIEs in our consolidated financial statements. Quota share reinsurance 2016 QSR Transaction Effective September 1, 2016, NMIC entered into a quota-share reinsurance (QSR) transaction (the 2016 QSR Transaction) with a panel of third-party reinsurers. Each of the third-party reinsurers has an insurer financial strength rating of A- or better by Standard and Poor’s Rating Services (S&P), A.M. Best or both. Under the 2016 QSR Transaction, NMIC ceded premiums written related to: • 25% of existing risk written on eligible policies as of August 31, 2016; • 100% of existing risk under our pool agreement with Fannie Mae; and • 25% of risk on eligible policies written from September 1, 2016 through December 31, 2017. 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. However, 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 reassuming the related risk. 2018 QSR Transaction Effective January 1, 2018, NMIC entered into a second quota share reinsurance treaty with a panel of third-party reinsurers (the 2018 QSR Transaction, together with the 2016 QSR Transaction, the QSR Transactions). Each of the third-party reinsurers has an insurer financial strength rating of A- or better by S&P, AM Best or both. Under the 2018 QSR Transaction, NMIC cedes premiums earned related to 25% of risk on eligible policies written in 2018 and 20% of risk on eligible policies written in 2019. The 2018 QSR Transaction is scheduled to terminate on December 31, 2029. However, 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 reassuming the related risk. NMIC may terminate either or both 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 this termination, ceded premiums written under the 2016 QSR Transaction will decrease 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 the amounts related to the QSR Transactions: For the three months ended March 31, 2019 March 31, 2018 (In Thousands) Ceded risk-in-force $ 4,534,353 $ 3,304,335 Ceded premiums written (18,845 ) (14,525 ) Ceded premiums earned (21,468 ) (16,218 ) Ceded claims and claim expenses 899 543 Ceding commission written 3,771 2,905 Ceding commission earned 4,206 3,151 Profit commission 12,061 9,201 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 QSR Transaction, 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, provided that the loss ratio on the loans covered under the 2016 QSR Transaction and 2018 QSR Transaction generally remains below 60% and 61% , respectively, as measured annually. Ceded claims and claim expenses under the QSR Transactions reduce NMIC's profit commission 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 our 2016 QSR Transaction was $3.1 million as of March 31, 2019 . In accordance with the terms of the 2018 QSR Transaction, 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 settled 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 reinsurance recoverable on loss reserves related to our 2018 QSR Transaction was $0.6 million as of March 31, 2019 .

Reserves for Insurance Claims a

Reserves for Insurance Claims and Claim Expenses	3 Months Ended
	Mar. 31, 2019
Insurance [Abstract]
Reserves for Insurance Claims and Claim Expenses	Reserves for Insurance Claims and Claim Expenses We establish reserves to recognize the estimated liability for insurance claims and claim expenses related to defaults on insured mortgage loans. Consistent with industry practice, we establish reserves for loans that have been reported to us by servicers as having been in default for at least 60 days, referred to as case reserves, and additional loans that we estimate (based on actuarial review) have been in default for at least 60 days that have not yet been reported to us by servicers, referred to as incurred but not reported (IBNR) reserves. We also establish claim expense reserves, which represent the estimated cost of the claim administration process, including legal and other fees, as well as other general expenses of administering the claims settlement process. As of March 31, 2019 , we had reserves for insurance claims and claim expenses of $15.5 million for 940 primary loans in default. During the three months ended March 31, 2019 , we paid 37 claims totaling $0.9 million , including 36 claims covered under the QSR Transactions representing $0.2 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 March 31, 2019 , 53 loans in the pool were past due by 60 days or more. These 53 loans represented approximately $3.3 million of RIF. Due to the size of the remaining deductible, the low level of notices of default (NODs) reported on loans in the pool through March 31, 2019 and the expected severity (all loans in the pool have loan-to-value ratios (LTV) ratios under 80% ), we did not establish any case or IBNR reserves for pool risk at March 31, 2019 . In connection with the settlement of pool claims, we applied $0.6 million to the pool deductible through March 31, 2019 . At March 31, 2019 , the remaining pool deductible was $9.7 million . We have not paid any pool claims to date. 100% of our pool RIF is reinsured under the 2016 QSR Transaction. The following table provides a reconciliation of the beginning and ending reserve balances for primary insurance claims and claim expenses: For the three months ended March 31, 2019 2018 (In Thousands) Beginning balance $ 12,811 $ 8,761 Less reinsurance recoverables (1) (3,001 ) (1,902 ) Beginning balance, net of reinsurance recoverables 9,810 6,859 Add claims incurred: Claims and claim expenses incurred: Current year (2) 3,909 1,940 Prior years (3) (1,166 ) (371 ) Total claims and claim expenses incurred 2,743 1,569 Less claims paid: Claims and claim expenses paid: Current year (2) — — Prior years (3) 694 371 Total claims and claim expenses paid 694 371 Reserve at end of period, net of reinsurance recoverables 11,859 8,057 Add reinsurance recoverables (1) 3,678 2,334 Ending balance $ 15,537 $ 10,391 (1) Related to ceded losses recoverable on the QSR Transactions, included in "Other Assets" on the Condensed Consolidated Balance Sheets. 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 had defaulted in a prior year and subsequently cured and later re-defaulted in the current year, that default would be included in the current year. Amounts are presented net of reinsurance. (3) Related to insured loans with defaults occurring in prior years, which have been continuously in default since that time. Amounts are presented net of reinsurance. The "claims incurred" section of the table above shows claims and claim expenses incurred on NODs for current and prior years, including IBNR reserves and is presented net of reinsurance. The amount of claims incurred relating to current year NODs represents the estimated amount of claims and claim expenses to be ultimately paid on such loans in default. We recognized $1.2 million and $0.4 million of favorable prior year development during the three months ended March 31, 2019 and 2018 , respectively, due to NOD cures and ongoing analysis of recent loss development trends. We may increase or decrease our original estimates as we learn additional information about individual defaults and claims and continue to observe and analyze loss development trends in our portfolio. Gross reserves of $10.4 million related to prior year defaults remained as of March 31, 2019 .

Earnings per Share (EPS)

Earnings per Share (EPS)	3 Months Ended
	Mar. 31, 2019
Earnings Per Share [Abstract]
Earnings per Share (EPS)	Earnings per Share (EPS) Basic earnings per share is based on the weighted average number of shares of common stock outstanding. Diluted earnings per share 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 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 earnings per share of common stock. For the three months ended March 31, 2019 2018 (In Thousands, except for per share data) Net income $ 32,899 $ 22,355 Basic weighted average shares outstanding 66,692 62,099 Basic earnings per share $ 0.49 $ 0.36 Net income $ 32,899 $ 22,355 Warrant gain, net of tax — (332 ) Diluted net income $ 32,899 $ 22,023 Basic weighted average shares outstanding 66,692 62,099 Dilutive effect of issuable shares 2,304 3,598 Diluted weighted average shares outstanding 68,996 65,697 Diluted earnings per share $ 0.48 $ 0.34 Anti-dilutive shares 754 169

Warrants

Warrants	3 Months Ended
	Mar. 31, 2019
Debt Disclosure [Abstract]
Warrants	Warrants We issued 992 thousand warrants in connection with a private placement of our common stock in April 2012. 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 March 31, 2019 , 67 thousand warrants were exercised resulting in the issuance of 39 thousand common shares. Upon exercise, we reclassified approximately $0.9 million of warrant fair value from warrant liability to additional paid-in capital, of which $0.3 million related to changes in fair value during the three months ended March 31, 2019 . During the three months ended March 31, 2018 , 54 thousand warrants were exercised resulting in the issuance of 26 thousand common shares. Upon exercise, we reclassified approximately $0.5 million of warrant fair value from warrant liability to additional paid-in capital, of which $0.1 million related to changes in fair value during the three months ended March 31, 2018 . We account for these warrants to purchase our common shares in accordance with ASC 470-20, Debt with Conversion and Other Options and ASC 815-40, Derivatives and Hedging - Contracts in Entity's Own Equity.

Income Taxes

Income Taxes	3 Months Ended
	Mar. 31, 2019
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 provision for income taxes for interim reporting periods is established based on our estimated annual effective tax rates for a given year. Our effective tax rate on our pre-tax income was 15.6% for the three months ended March 31, 2019 , compared to 15.7% for the three months ended March 31, 2018 . As a mortgage guaranty insurance company, we are eligible to claim a tax deduction of 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 months ended March 31, 2019 represents a change in our net deferred tax liability.

Leases

Leases	3 Months Ended
	Mar. 31, 2019
Leases [Abstract]
Leases	Leases We have two operating lease agreements related to our corporate headquarters and a data center facility for which we recognized operating right-of-use (ROU) assets and lease liabilities of $7.7 million and $8.9 million , respectively, as of March 31, 2019 . As of March 31, 2019 , we did not have any finance leases. We recognize ROU assets and lease liabilities in connection with the adoption of ASU 2016-02, Leases (Topic 842). ROU assets and lease liabilities are established based on the estimated present value of lease payments over the relevant lease term. We estimate a discount rate for each lease based on our estimated incremental borrowing rate at the commencement date of the relevant lease. Right-of-use assets obtained in exchange for new operating lease liabilities for the three months ended March 31, 2019 were $8.1 million . The following table provides a summary of our ROU asset and lease liability assumptions as of March 31, 2019 : Weighted-average remaining lease term 4 years Weighted-average discount rate 6.21 % Cash paid and lease expenses recognized on our operating lease liabilities for the three months ended March 31, 2019 were $0.6 million . Future payments due under our existing operating leases as of March 31, 2019 are as follows: As of March 31, 2019 (In Thousands) 2019 $ 1,853 2020 2,537 2021 2,609 2022 2,574 2023 462 Total undiscounted lease payments 10,035 Less effects of discounting (1,164 ) Present value of lease payments $ 8,871 Lease expense is recorded in underwriting and operating expenses on the consolidated statements of operations. Our existing operating leases have terms that range from three to five years. The lease for our corporate headquarters includes an option to renew for an additional five years at prevailing market rates at time of renewal. We have not included this renewal option in our calculation of minimum lease payments as it is not reasonably certain to be exercised. As of December 31, 2018, the future minimum lease payments as accounted for prior to our adoption of ASU 2016-02, Leases (Topic 842) are as follows: Year ending December 31, (In Thousands) 2019 $ 2,346 2020 2,417 2021 2,489 2022 2,564 2023 463 Totals $ 10,279

Regulatory Information

Regulatory Information	3 Months Ended
	Mar. 31, 2019
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. 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's combined statutory net income (loss) was as follows: For the three months ended March 31, 2019 2018 (In Thousands) Statutory net income (loss) $ (927 ) $ (6,814 ) NMIC and Re One's combined statutory surplus, contingency reserve and risk-to-capital (RTC) ratios were as follows: March 31, 2019 December 31, 2018 (Dollars In Thousands) Statutory surplus $ 431,824 $ 430,785 Contingency reserve 375,823 332,702 RTC Ratio 14:1 13.1:1 NMIH is not subject to any limitations on its ability to pay dividends except those generally applicable to corporations that are incorporated in Delaware. Delaware corporate 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's ability to pay dividends to NMIH is subject to Wisconsin OCI notice or approval. Certain other states in which NMIC is licensed also have statutes or regulations that restrict its ability to pay dividends. Since inception, NMIC and Re One have not paid any dividends to NMIH.

Organization, Basis of Presen_2

Organization, Basis of Presentation and Summary of Accounting Principles (Policies)	3 Months Ended
	Mar. 31, 2019
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, 2018 , included in our 2018 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. Certain reclassifications to our previously reported financial information have been made to conform to current period presentation. 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, 2019 .
Recent Accounting Pronouncements	Recent Accounting Pronouncements - Adopted In February 2016, the Financial Accounting Standards Board (FASB) issued Accounting Standards Update (ASU) 2016-02, Leases (Topic 842). This update requires that businesses recognize rights and obligations associated with certain leases as assets and liabilities on the balance sheet. The standard also requires additional disclosures regarding the amount, timing, and uncertainty of cash flows arising from leases. We adopted this ASU on January 1, 2019 using the modified-retrospective method and applied it prospectively as of the effective date, without adjusting comparative periods presented as permitted by ASU 2018-11, Leases (Topic 842), Targeted Improvements . Adoption of this new standard increased our assets and liabilities by $7.6 million in connection with the recognition of right-of-use assets and lease liabilities, primarily related to the operating lease on our corporate headquarters. Adoption of this standard did not impact our consolidated statements of operations or cash flows. See Note 10, " Leases " for additional information related to our leases. In July 2017, the FASB issued ASU 2017-11, Earnings Per Share (Topic 260), Distinguishing Liabilities from Equity (Topic 480), and Derivatives and Hedging (Topic 815). This update is intended to simplify the accounting for certain equity-linked financial instruments. We adopted this ASU on January 1, 2019. Adoption of this standard had no impact on our consolidated financial statements. In June 2018, the FASB issued ASU 2018-07, Compensation-Stock Compensation (Topic 718). This update expands the scope of Topic 718 to include share-based payments made to non-employees in connection with the acquisition of goods and services. We adopted this ASU on January 1, 2019. Adoption of this standard had no impact on our financial results at this time as we have not made any share-based grants to non-employees as defined in ASC 718-10-20. Recent Accounting Pronouncements - Not Yet Adopted In June 2016, the FASB issued ASU 2016-13, Financial Instruments-Credit Losses (Topic 326). This update requires companies to measure all expected credit losses for financial assets held at the reporting date. The standard also amends the accounting for credit losses on available-for-sale debt securities and purchased financial assets with credit deterioration. The standard will take effect for public business entities for fiscal years, and interim periods within those fiscal years, beginning after December 15, 2019. We are currently reviewing the impact the adoption of this ASU will have, if any, on our financial assets. We do not expect it to impact our accounting for insurance claims and claim expenses as these items are not in the scope of this ASU. In August 2018, the FASB issued ASU 2018-12, Targeted Improvements to the Accounting for Long-Duration Contracts . This update provides guidance to the existing recognition, measurement, presentation and disclosure requirements for long-duration contracts issued by an insurance entity. The standard will take effect for public business entities for fiscal years, and interim periods within those fiscal years, beginning after December 15, 2020. We are currently evaluating the impact the adoption of this ASU will have, if any, on our consolidated financial statements. In August 2018, the FASB issued ASU 2018-13, Fair Value Measurement (Topic 820). This update modifies the fair value measurement disclosure requirements of ASC 820. The standard will take effect for public business entities for fiscal years, and interim periods within those fiscal years, beginning after December 15, 2019. We are currently evaluating the impact the adoption of this ASU will have, if any, on our fair value of financial instruments disclosures. In August 2018, the FASB issued ASU 2018-15, Intangibles - Goodwill and Other - Internal-Use Software (Subtopic 350-40). This update applies to cloud computing arrangements hosted by a vendor and provides companies with guidance on the criteria for capitalizing implementation, set-up and other up-front costs incurred in association with these arrangements. The standard will take effect for public business entities for fiscal years, and interim periods within those fiscal years, beginning after December 15, 2019. We are currently evaluating the impact the adoption of this ASU will have, if any, on our consolidated financial statements.
Earnings Per Share	Basic earnings per share is based on the weighted average number of shares of common stock outstanding. Diluted earnings per share 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 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.

Investments (Tables)

Investments (Tables)	3 Months Ended
	Mar. 31, 2019
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 March 31, 2019 (In Thousands) U.S. Treasury securities and obligations of U.S. government agencies $ 48,189 $ 86 $ (696 ) $ 47,579 Municipal debt securities 91,833 671 (331 ) 92,173 Corporate debt securities 613,016 7,471 (2,871 ) 617,616 Asset-backed securities 156,258 1,241 (125 ) 157,374 Total bonds 909,296 9,469 (4,023 ) 914,742 Short-term investments 25,416 65 — 25,481 Total investments $ 934,712 $ 9,534 $ (4,023 ) $ 940,223 Amortized Gross Unrealized Fair Gains Losses As of December 31, 2018 (In Thousands) U.S. Treasury securities and obligations of U.S. government agencies $ 48,171 $ 35 $ (1,376 ) $ 46,830 Municipal debt securities 92,014 206 (963 ) 91,257 Corporate debt securities 554,079 847 (11,688 ) 543,238 Asset-backed securities 171,990 792 (1,457 ) 171,325 Total bonds 866,254 1,880 (15,484 ) 852,650 Short-term investments 58,733 107 — 58,840 Total investments $ 924,987 $ 1,987 $ (15,484 ) $ 911,490
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 March 31, 2019 and December 31, 2018 : March 31, 2019 December 31, 2018 Financial 38 % 38 % Consumer 26 27 Communications 11 12 Utilities 10 7 Industrial 7 7 Technology 5 6 Energy 2 2 Other 1 1 Total 100 % 100 %
Schedule of Investments by Maturity	The amortized cost and fair values of available-for-sale securities as of March 31, 2019 and December 31, 2018 , 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 March 31, 2019 Amortized Fair (In Thousands) Due in one year or less $ 47,004 $ 46,989 Due after one through five years 399,669 400,793 Due after five through ten years 314,593 317,471 Due after ten years 17,188 17,596 Asset-backed securities 156,258 157,374 Total investments $ 934,712 $ 940,223 As of December 31, 2018 Amortized Fair (In Thousands) Due in one year or less $ 76,087 $ 76,104 Due after one through five years 352,282 347,701 Due after five through ten years 318,728 310,633 Due after ten years 5,900 5,727 Asset-backed securities 171,990 171,325 Total investments $ 924,987 $ 911,490
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 March 31, 2019 (Dollars in Thousands) U.S. Treasury securities and obligations of U.S. government agencies — $ — $ — 17 $ 37,425 $ (696 ) 17 $ 37,425 $ (696 ) Municipal debt securities (1) 1 2,000 — 19 33,034 (331 ) 20 35,034 (331 ) Corporate debt securities 23 43,094 (423 ) 89 158,174 (2,448 ) 112 201,268 (2,871 ) Asset-backed securities 10 18,173 (46 ) 20 28,453 (79 ) 30 46,626 (125 ) Short-term investments (1) 1 994 — — — — 1 994 — Total 35 $ 64,261 $ (469 ) 145 $ 257,086 $ (3,554 ) 180 $ 321,347 $ (4,023 ) (1) Includes securities with unrealized losses of less than 12 months which are not identifiable in the schedule due to rounding. 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, 2018 (Dollars in Thousands) U.S. Treasury securities and obligations of U.S. government agencies — $ — $ — 19 $ 41,817 $ (1,376 ) 19 $ 41,817 $ (1,376 ) Municipal debt securities 4 7,409 (11 ) 31 58,658 (952 ) 35 66,067 (963 ) Corporate debt securities 118 226,477 (3,952 ) 126 221,675 (7,736 ) 244 448,152 (11,688 ) Asset-backed securities 25 36,017 (1,136 ) 22 33,988 (321 ) 47 70,005 (1,457 ) Total 147 $ 269,903 $ (5,099 ) 198 $ 356,138 $ (10,385 ) 345 $ 626,041 $ (15,484 )
Schedule of Net Investment Income	The following table presents the components of net investment income: For the three months ended March 31, 2019 2018 (In Thousands) Investment income $ 7,496 $ 4,782 Investment expenses (113 ) (208 ) Net investment income $ 7,383 $ 4,574
Schedule of Net Realized Investment Gains (Losses)	The following table presents the components of net realized investment losses: For the three months ended March 31, 2019 2018 (In Thousands) Gross realized investment gains $ 195 $ — Gross realized investment losses (382 ) — Net realized investment losses $ (187 ) $ —

Fair Value of Financial Instr_2

Fair Value of Financial Instruments (Tables)	3 Months Ended
	Mar. 31, 2019
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 March 31, 2019 (In Thousands) U.S. Treasury securities and obligations of U.S. government agencies $ 47,579 $ — $ — $ 47,579 Municipal debt securities — 92,173 — 92,173 Corporate debt securities — 617,616 — 617,616 Asset-backed securities — 157,374 — 157,374 Cash, cash equivalents and short-term investments 65,242 — — 65,242 Total assets $ 112,821 $ 867,163 $ — $ 979,984 Warrant liability — — 11,831 11,831 Total liabilities $ — $ — $ 11,831 $ 11,831 Fair Value Measurements Using Quoted Prices in Significant Other Significant Fair Value As of December 31, 2018 (In Thousands) U.S. Treasury securities and obligations of U.S. government agencies $ 46,830 $ — $ — $ 46,830 Municipal debt securities — 91,257 — 91,257 Corporate debt securities — 543,238 — 543,238 Asset-backed securities — 171,325 — 171,325 Cash, cash equivalents and short-term investments 84,134 — — 84,134 Total assets $ 130,964 $ 805,820 $ — $ 936,784 Warrant liability — — 7,296 7,296 Total liabilities $ — $ — $ 7,296 $ 7,296
Roll-Forward of Level 3 Liabilities Measured at Fair Value	The following is a roll-forward of Level 3 liabilities measured at fair value: For the three months ended March 31, Warrant Liability 2019 2018 (In Thousands) Balance, January 1 $ 7,296 $ 7,472 Change in fair value of warrant liability included in earnings 5,479 (420 ) Issuance of common stock on warrant exercise (944 ) (489 ) Balance, March 31 $ 11,831 $ 6,563
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 March 31, 2019 2018 Common stock price $ 25.87 $ 16.55 Risk free interest rate 2.21 - 2.31% 2.37 % Expected life 1.67 - 3.06 years 2.59 years Expected volatility 42.30 - 45.7% 30.1 % Dividend yield 0% 0%

Debt (Tables)

Debt (Tables)	3 Months Ended
	Mar. 31, 2019
Debt Disclosure [Abstract]
Schedule of Future Principal Payments	Future principal payments due under the 2018 Term Loan as of March 31, 2019 are as follows: As of March 31, 2019 Principal (In thousands) 2019 $ 1,125 2020 1,500 2021 1,500 2022 1,500 2023 143,250 Total $ 148,875

Reinsurance (Tables)

Reinsurance (Tables)	3 Months Ended
	Mar. 31, 2019
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 March 31, 2019 March 31, 2018 (In Thousands) Net premiums written Direct $ 81,730 $ 66,027 Ceded (1) (9,807 ) (6,997 ) Net premiums written $ 71,923 $ 59,030 Net premiums earned Direct $ 86,298 $ 63,604 Ceded (1) (12,430 ) (8,690 ) Net premiums earned $ 73,868 $ 54,914 (1) Net of profit commission The following table shows the amounts related to the QSR Transactions: For the three months ended March 31, 2019 March 31, 2018 (In Thousands) Ceded risk-in-force $ 4,534,353 $ 3,304,335 Ceded premiums written (18,845 ) (14,525 ) Ceded premiums earned (21,468 ) (16,218 ) Ceded claims and claim expenses 899 543 Ceding commission written 3,771 2,905 Ceding commission earned 4,206 3,151 Profit commission 12,061 9,201

Reserves for Insurance Claims_2

Reserves for Insurance Claims and Claim Expenses (Tables)	3 Months Ended
	Mar. 31, 2019
Insurance [Abstract]
Reconciliation of Liability for Insurance Claims and Claim Expenses	The following table provides a reconciliation of the beginning and ending reserve balances for primary insurance claims and claim expenses: For the three months ended March 31, 2019 2018 (In Thousands) Beginning balance $ 12,811 $ 8,761 Less reinsurance recoverables (1) (3,001 ) (1,902 ) Beginning balance, net of reinsurance recoverables 9,810 6,859 Add claims incurred: Claims and claim expenses incurred: Current year (2) 3,909 1,940 Prior years (3) (1,166 ) (371 ) Total claims and claim expenses incurred 2,743 1,569 Less claims paid: Claims and claim expenses paid: Current year (2) — — Prior years (3) 694 371 Total claims and claim expenses paid 694 371 Reserve at end of period, net of reinsurance recoverables 11,859 8,057 Add reinsurance recoverables (1) 3,678 2,334 Ending balance $ 15,537 $ 10,391 (1) Related to ceded losses recoverable on the QSR Transactions, included in "Other Assets" on the Condensed Consolidated Balance Sheets. 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 had defaulted in a prior year and subsequently cured and later re-defaulted in the current year, that default would be included in the current year. Amounts are presented net of reinsurance. (3) Related to insured loans with defaults occurring in prior years, which have been continuously in default since that time.

Earnings per Share (EPS) (Table

Earnings per Share (EPS) (Tables)	3 Months Ended
	Mar. 31, 2019
Earnings Per Share [Abstract]
Schedule of Earnings per Share, Basic and Diluted	The following table reconciles the net income and the weighted average shares of common stock outstanding used in the computations of basic and diluted earnings per share of common stock. For the three months ended March 31, 2019 2018 (In Thousands, except for per share data) Net income $ 32,899 $ 22,355 Basic weighted average shares outstanding 66,692 62,099 Basic earnings per share $ 0.49 $ 0.36 Net income $ 32,899 $ 22,355 Warrant gain, net of tax — (332 ) Diluted net income $ 32,899 $ 22,023 Basic weighted average shares outstanding 66,692 62,099 Dilutive effect of issuable shares 2,304 3,598 Diluted weighted average shares outstanding 68,996 65,697 Diluted earnings per share $ 0.48 $ 0.34 Anti-dilutive shares 754 169

Leases (Tables)

Leases (Tables)	3 Months Ended
	Mar. 31, 2019
Leases [Abstract]
Summary of Right-of-Use Asset and Lease Liability Activity and Assumptions	The following table provides a summary of our ROU asset and lease liability assumptions as of March 31, 2019 : Weighted-average remaining lease term 4 years Weighted-average discount rate 6.21 %
Schedule of Future Payments Due Under Operating Leases	Future payments due under our existing operating leases as of March 31, 2019 are as follows: As of March 31, 2019 (In Thousands) 2019 $ 1,853 2020 2,537 2021 2,609 2022 2,574 2023 462 Total undiscounted lease payments 10,035 Less effects of discounting (1,164 ) Present value of lease payments $ 8,871
Schedule of Future Minimum Lease Payments as Accounted For Prior to Adoption of ASU 2016-02	As of December 31, 2018, the future minimum lease payments as accounted for prior to our adoption of ASU 2016-02, Leases (Topic 842) are as follows: Year ending December 31, (In Thousands) 2019 $ 2,346 2020 2,417 2021 2,489 2022 2,564 2023 463 Totals $ 10,279

Regulatory Information (Tables)

Regulatory Information (Tables)	3 Months Ended
	Mar. 31, 2019
Insurance [Abstract]
Schedule of Statutory Net Income (Loss), Surplus, Contingency Reserve and Risk-to-Capital Ratio	NMIC and Re One's combined statutory net income (loss) was as follows: For the three months ended March 31, 2019 2018 (In Thousands) Statutory net income (loss) $ (927 ) $ (6,814 ) NMIC and Re One's combined statutory surplus, contingency reserve and risk-to-capital (RTC) ratios were as follows: March 31, 2019 December 31, 2018 (Dollars In Thousands) Statutory surplus $ 431,824 $ 430,785 Contingency reserve 375,823 332,702 RTC Ratio 14:1 13.1:1

Organization, Basis of Presen_3

Organization, Basis of Presentation and Summary of Accounting Principles - Narrative (Details)	Mar. 31, 2019state
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Number of states in which the entity operates	50

Organization, Basis of Presen_4

Organization, Basis of Presentation and Summary of Accounting Principles - Recent Accounting Pronouncements (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Jan. 01, 2019
New Accounting Pronouncements [Line Items]
Right-of-use assets	$ 7,700
Lease liabilities	$ 8,871
ASU No. 2016-02
New Accounting Pronouncements [Line Items]
Right-of-use assets		$ 7,600
Lease liabilities		$ 7,600

Investments - Fair Values and G

Investments - Fair Values and Gross Unrealized Gains and Losses (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	$ 934,712	$ 924,987
Gross Unrealized Gains	9,534	1,987
Gross Unrealized Losses	(4,023)	(15,484)
Fair value of securities	940,223	911,490
U.S. Treasury securities and obligations of U.S. government agencies
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	48,189	48,171
Gross Unrealized Gains	86	35
Gross Unrealized Losses	(696)	(1,376)
Fair value of securities	47,579	46,830
Municipal debt securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	91,833	92,014
Gross Unrealized Gains	671	206
Gross Unrealized Losses	(331)	(963)
Fair value of securities	92,173	91,257
Corporate debt securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	613,016	554,079
Gross Unrealized Gains	7,471	847
Gross Unrealized Losses	(2,871)	(11,688)
Fair value of securities	617,616	543,238
Asset-backed securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	156,258	171,990
Gross Unrealized Gains	1,241	792
Gross Unrealized Losses	(125)	(1,457)
Fair value of securities	157,374	171,325
Total bonds
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	909,296	866,254
Gross Unrealized Gains	9,469	1,880
Gross Unrealized Losses	(4,023)	(15,484)
Fair value of securities	914,742	852,650
Short-term investments
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	25,416	58,733
Gross Unrealized Gains	65	107
Gross Unrealized Losses	0	0
Fair value of securities	$ 25,481	$ 58,840

Investments - Corporate Debt Se

Investments - Corporate Debt Securities by Industry Group (Details)	Mar. 31, 2019	Dec. 31, 2018
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%	38.00%
Consumer
Debt Securities By Industry [Line Items]
Corporate debt securities as component of total (percent)	26.00%	27.00%
Communications
Debt Securities By Industry [Line Items]
Corporate debt securities as component of total (percent)	11.00%	12.00%
Utilities
Debt Securities By Industry [Line Items]
Corporate debt securities as component of total (percent)	10.00%	7.00%
Industrial
Debt Securities By Industry [Line Items]
Corporate debt securities as component of total (percent)	7.00%	7.00%
Technology
Debt Securities By Industry [Line Items]
Corporate debt securities as component of total (percent)	5.00%	6.00%
Energy
Debt Securities By Industry [Line Items]
Corporate debt securities as component of total (percent)	2.00%	2.00%
Other
Debt Securities By Industry [Line Items]
Corporate debt securities as component of total (percent)	1.00%	1.00%

Investments - Scheduled Maturit

Investments - Scheduled Maturities (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Amortized Cost
Due in one year or less	$ 47,004	$ 76,087
Due after one through five years	399,669	352,282
Due after five through ten years	314,593	318,728
Due after ten years	17,188	5,900
Asset-backed securities	156,258	171,990
Amortized Cost	934,712	924,987
Fair Value
Due in one year or less	46,989	76,104
Due after one through five years	400,793	347,701
Due after five through ten years	317,471	310,633
Due after ten years	17,596	5,727
Asset-backed securities	157,374	171,325
Fair Value	$ 940,223	$ 911,490

Investments - Aging of Unrealiz

Investments - Aging of Unrealized Losses (Details) $ in Thousands	Mar. 31, 2019USD ($)security	Dec. 31, 2018USD ($)security
Debt Securities, Available-for-sale [Line Items]
Number of securities, less than 12 months | security	35	147
Fair value, less than 12 months	$ 64,261	$ 269,903
Unrealized losses, less than 12 months	$ (469)	$ (5,099)
Number of securities,12 months or greater | security	145	198
Fair value, 12 months or greater	$ 257,086	$ 356,138
Unrealized losses, 12 months or greater	$ (3,554)	$ (10,385)
Number of securities, total | security	180	345
Fair value	$ 321,347	$ 626,041
Unrealized Losses	$ (4,023)	$ (15,484)
U.S. Treasury securities and obligations of U.S. government agencies
Debt Securities, Available-for-sale [Line Items]
Number of securities, less than 12 months | security	0	0
Fair value, less than 12 months	$ 0	$ 0
Unrealized losses, less than 12 months	$ 0	$ 0
Number of securities,12 months or greater | security	17	19
Fair value, 12 months or greater	$ 37,425	$ 41,817
Unrealized losses, 12 months or greater	$ (696)	$ (1,376)
Number of securities, total | security	17	19
Fair value	$ 37,425	$ 41,817
Unrealized Losses	$ (696)	$ (1,376)
Municipal debt securities
Debt Securities, Available-for-sale [Line Items]
Number of securities, less than 12 months | security	1	4
Fair value, less than 12 months	$ 2,000	$ 7,409
Unrealized losses, less than 12 months	$ 0	$ (11)
Number of securities,12 months or greater | security	19	31
Fair value, 12 months or greater	$ 33,034	$ 58,658
Unrealized losses, 12 months or greater	$ (331)	$ (952)
Number of securities, total | security	20	35
Fair value	$ 35,034	$ 66,067
Unrealized Losses	$ (331)	$ (963)
Corporate debt securities
Debt Securities, Available-for-sale [Line Items]
Number of securities, less than 12 months | security	23	118
Fair value, less than 12 months	$ 43,094	$ 226,477
Unrealized losses, less than 12 months	$ (423)	$ (3,952)
Number of securities,12 months or greater | security	89	126
Fair value, 12 months or greater	$ 158,174	$ 221,675
Unrealized losses, 12 months or greater	$ (2,448)	$ (7,736)
Number of securities, total | security	112	244
Fair value	$ 201,268	$ 448,152
Unrealized Losses	$ (2,871)	$ (11,688)
Asset-backed securities
Debt Securities, Available-for-sale [Line Items]
Number of securities, less than 12 months | security	10	25
Fair value, less than 12 months	$ 18,173	$ 36,017
Unrealized losses, less than 12 months	$ (46)	$ (1,136)
Number of securities,12 months or greater | security	20	22
Fair value, 12 months or greater	$ 28,453	$ 33,988
Unrealized losses, 12 months or greater	$ (79)	$ (321)
Number of securities, total | security	30	47
Fair value	$ 46,626	$ 70,005
Unrealized Losses	$ (125)	$ (1,457)
Short-term investments
Debt Securities, Available-for-sale [Line Items]
Number of securities, less than 12 months | security	1
Fair value, less than 12 months	$ 994
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	1
Fair value	$ 994
Unrealized Losses	$ 0

Investments - Net Investment In

Investments - Net Investment Income (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Investment Income, Net [Abstract]
Investment income	$ 7,496	$ 4,782
Investment expenses	(113)	(208)
Net investment income	$ 7,383	$ 4,574

Investments - Net Realized Inve

Investments - Net Realized Investment Gains (Losses) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Investments, Debt and Equity Securities [Abstract]
Gross realized investment gains	$ 195	$ 0
Gross realized investment losses	(382)	0
Net realized investment losses	$ (187)	$ 0

Investments - Narrative (Detail

Investments - Narrative (Details) - USD ($)	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Dec. 31, 2018
Debt Securities, Available-for-sale [Line Items]
Unrealized loss position, accumulated loss	$ 4,023,000		$ 15,484,000
Unrealized loss position, 12 months or greater	3,554,000		10,385,000
Other-than-temporary impairment	400,000	$ 0
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	5,400,000		5,300,000
Unrealized loss position, accumulated loss	696,000		1,376,000
Unrealized loss position, 12 months or greater	$ 696,000		$ 1,376,000

Fair Value of Financial Instr_3

Fair Value of Financial Instruments - Assets and Liabilities at Fair Value (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value of securities	$ 940,223	$ 911,490
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	47,579	46,830
Municipal debt securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value of securities	92,173	91,257
Corporate debt securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value of securities	617,616	543,238
Asset-backed securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value of securities	157,374	171,325
Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash, cash equivalents and short-term investments	65,242	84,134
Total assets	979,984	936,784
Warrant liability	11,831	7,296
Total liabilities	11,831	7,296
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	47,579	46,830
Recurring | Municipal debt securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value of securities	92,173	91,257
Recurring | Corporate debt securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value of securities	617,616	543,238
Recurring | Asset-backed securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value of securities	157,374	171,325
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	65,242	84,134
Total assets	112,821	130,964
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	47,579	46,830
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	867,163	805,820
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	92,173	91,257
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	617,616	543,238
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	157,374	171,325
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	11,831	7,296
Total liabilities	11,831	7,296
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	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Roll-forward of Level 3 liabilities:
Beginning balance	$ 7,296	$ 7,472
Change in fair value of warrant liability included in earnings	5,479	(420)
Issuance of common stock on warrant exercise	(944)	(489)
Ending balance	$ 11,831	$ 6,563

Fair Value of Financial Instr_5

Fair Value of Financial Instruments - Valuation Assumptions for Warrant Liabilities (Details) $ in Thousands	Mar. 31, 2019USD ($)$ / shares	Dec. 31, 2018USD ($)	Mar. 31, 2018$ / shares
Key Inputs and Assumptions, Valuation Techniques
Term loan | $	$ 146,503	$ 146,757
Significant Unobservable Inputs (Level 3) | Valuation Technique, Option Pricing Model | Common stock price
Key Inputs and Assumptions, Valuation Techniques
Warrant liability, measurement input | $ / shares	25.87		16.55
Significant Unobservable Inputs (Level 3) | Valuation Technique, Option Pricing Model | Risk free interest rate
Key Inputs and Assumptions, Valuation Techniques
Warrant liability, measurement input			0.0237
Significant Unobservable Inputs (Level 3) | Valuation Technique, Option Pricing Model | Risk free interest rate | Minimum
Key Inputs and Assumptions, Valuation Techniques
Warrant liability, measurement input	0.0221
Significant Unobservable Inputs (Level 3) | Valuation Technique, Option Pricing Model | Risk free interest rate | Maximum
Key Inputs and Assumptions, Valuation Techniques
Warrant liability, measurement input	0.0231
Significant Unobservable Inputs (Level 3) | Valuation Technique, Option Pricing Model | Expected life
Key Inputs and Assumptions, Valuation Techniques
Warrant liability, expected life (in years)			2 years 7 months 2 days
Significant Unobservable Inputs (Level 3) | Valuation Technique, Option Pricing Model | Expected life | Minimum
Key Inputs and Assumptions, Valuation Techniques
Warrant liability, expected life (in years)	1 year 8 months 2 days
Significant Unobservable Inputs (Level 3) | Valuation Technique, Option Pricing Model | Expected life | Maximum
Key Inputs and Assumptions, Valuation Techniques
Warrant liability, expected life (in years)	3 years 22 days
Significant Unobservable Inputs (Level 3) | Valuation Technique, Option Pricing Model | Expected volatility
Key Inputs and Assumptions, Valuation Techniques
Warrant liability, measurement input			0.301
Significant Unobservable Inputs (Level 3) | Valuation Technique, Option Pricing Model | Expected volatility | Minimum
Key Inputs and Assumptions, Valuation Techniques
Warrant liability, measurement input	0.423
Significant Unobservable Inputs (Level 3) | Valuation Technique, Option Pricing Model | Expected volatility | Maximum
Key Inputs and Assumptions, Valuation Techniques
Warrant liability, measurement input	0.457
Significant Unobservable Inputs (Level 3) | Valuation Technique, Option Pricing Model | Dividend yield
Key Inputs and Assumptions, Valuation Techniques
Warrant liability, measurement input	0		0

Debt - Narrative (Details)

Debt - Narrative (Details) - USD ($)	May 24, 2018	Mar. 31, 2019	Mar. 31, 2018
Debt Instrument [Line Items]
Term loan		$ 148,875,000
Interest expense		$ 3,061,000	$ 3,419,000
Secured Debt | 2018 Term Loan
Debt Instrument [Line Items]
Debt instrument face amount	$ 150,000,000
Debt instrument term (years)	5 years
Interest rate during period (percent)		7.25%
Frequency of periodic payment		Quarterly
Periodic payment of principal		$ 375,000
Interest expense		2,800,000
Unamortized issuance costs		$ 2,400,000
Debt instrument covenant, maximum debt-to-total capitalization ratio		35.00%
Secured Debt | 2018 Term Loan | Eurodollar
Debt Instrument [Line Items]
Variable rate floor (percent)		1.00%
Basis spread on variable rate (percent)		4.75%
Senior Secured Debt | 2015 Term Loan
Debt Instrument [Line Items]
Debt instrument face amount	$ 150,000,000
Revolving Credit Facility | 2018 Revolving Credit Facility
Debt Instrument [Line Items]
Debt instrument term (years)	3 years
Credit facility borrowing capacity	$ 85,000,000
Debt instrument covenant, maximum debt-to-total capitalization ratio		35.00%
Borrowings outstanding		$ 0
Commitment fee (percent)		0.50%
Commitment fees in interest expense		$ 100,000
Debt issuance costs	$ 1,500,000
Interest expense from amortization of debt issuance costs		100,000
Remaining deferred issuance costs, net of accumulated amortization		$ 1,100,000
Revolving Credit Facility | 2018 Revolving Credit Facility | Minimum
Debt Instrument [Line Items]
Commitment fee (percent)		0.30%
Revolving Credit Facility | 2018 Revolving Credit Facility | Maximum
Debt Instrument [Line Items]
Commitment fee (percent)		0.60%
Revolving Credit Facility | 2018 Revolving Credit Facility | Base Rate
Debt Instrument [Line Items]
Variable rate floor (percent)		1.00%
Revolving Credit Facility | 2018 Revolving Credit Facility | Base Rate | Minimum
Debt Instrument [Line Items]
Basis spread on variable rate (percent)		1.00%
Revolving Credit Facility | 2018 Revolving Credit Facility | Base Rate | Maximum
Debt Instrument [Line Items]
Basis spread on variable rate (percent)		2.50%
Revolving Credit Facility | 2018 Revolving Credit Facility | Eurodollar
Debt Instrument [Line Items]
Variable rate floor (percent)		0.00%
Revolving Credit Facility | 2018 Revolving Credit Facility | Eurodollar | Minimum
Debt Instrument [Line Items]
Basis spread on variable rate (percent)		2.00%
Revolving Credit Facility | 2018 Revolving Credit Facility | Eurodollar | Maximum
Debt Instrument [Line Items]
Basis spread on variable rate (percent)		3.50%

Debt - Schedule of Future Princ

Debt - Schedule of Future Principal Payments (Details) $ in Thousands	Mar. 31, 2019USD ($)
Future Principal Payments [Abstract]
2019	$ 1,125
2020	1,500
2021	1,500
2022	1,500
2023	143,250
Total	$ 148,875

Reinsurance - Narrative (Detail

Reinsurance - Narrative (Details) - USD ($) $ in Thousands	Apr. 01, 2019	Jul. 31, 2018	May 31, 2017	Mar. 31, 2019	Mar. 31, 2018	Dec. 31, 2018	Dec. 31, 2017
Ceded Credit Risk [Line Items]
Restricted cash				$ 1,422		$ 1,414
Reinsurance recoverable on unpaid claims				$ 3,678	$ 2,334	$ 3,001	$ 1,902
ILN Transactions
Ceded Credit Risk [Line Items]
Optional termination right, percent of reinsurance coverage threshold				10.00%
Mortgage-linked Debt | 2017 ILN Notes | Oaktown Re Ltd
Ceded Credit Risk [Line Items]
Proceeds from issuance of notes			$ 211,300
Mortgage-linked Debt | 2018 ILN Notes | Oaktown Re Ltd
Ceded Credit Risk [Line Items]
Proceeds from issuance of notes		$ 264,500
Third-Party Reinsurers | 2017 ILN Transaction
Ceded Credit Risk [Line Items]
Aggregate excess of loss reinsurance coverage				$ 117,400
Aggregate excess of loss reinsurance retained by company			126,800	124,700
Risk premiums paid				1,400	$ 1,600
Third-Party Reinsurers | 2017 ILN Transaction | Maximum
Ceded Credit Risk [Line Items]
Aggregate excess of loss reinsurance coverage			$ 211,300
Reinsurance coverage, term of underlying mortgage amortization (in years)			10 years
Anticipated payment related to annual operating expenses				300
Third-Party Reinsurers | 2018 ILN Transaction
Ceded Credit Risk [Line Items]
Aggregate excess of loss reinsurance coverage				264,500
Aggregate excess of loss reinsurance retained by company		125,300		125,300
Risk premiums paid				1,700
Third-Party Reinsurers | 2018 ILN Transaction | Maximum
Ceded Credit Risk [Line Items]
Aggregate excess of loss reinsurance coverage		$ 264,500
Reinsurance coverage, term of underlying mortgage amortization (in years)		10 years
Anticipated payment related to annual operating expenses				$ 250
Third-Party Reinsurers | QSR Transactions
Ceded Credit Risk [Line Items]
Ceding commissions under 2016 QSR Transaction				20.00%
Third-Party Reinsurers | 2018 QSR Transaction
Ceded Credit Risk [Line Items]
Threshold for loss ratio on loans to qualify for profit commission				61.00%
Reinsurance recoverable on unpaid claims				$ 600
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 | 2016 QSR Transaction
Ceded Credit Risk [Line Items]
Percent of premiums ceded under QSR Transaction				25.00%
Threshold for loss ratio on loans to qualify for profit commission				60.00%
Reinsurance recoverable on unpaid claims				$ 3,100
Third-Party Reinsurers | 2016 QSR Transaction | Subsequent Event
Ceded Credit Risk [Line Items]
Percent of premiums ceded under QSR Transaction	20.50%
Previously ceded primary RIF recaptured	$ 500,000
Third-Party Reinsurers | Existing Risk Written Policies
Ceded Credit Risk [Line Items]
Percent of premiums ceded under QSR Transaction				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 from September 1, 2016 through December 31, 2017
Ceded Credit Risk [Line Items]
Percent of premiums ceded under QSR Transaction				25.00%

Reinsurance - Effect of Reinsur

Reinsurance - Effect of Reinsurance Agreements on Premiums Written and Earned (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Net premiums written
Direct	$ 81,730	$ 66,027
Ceded	(9,807)	(6,997)
Net premiums written	71,923	59,030
Net premiums earned
Direct	86,298	63,604
Ceded	(12,430)	(8,690)
Net premiums earned	$ 73,868	$ 54,914

Reinsurance - Amounts Ceded Rel

Reinsurance - Amounts Ceded Related to QSR Transactions (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Ceded Credit Risk [Line Items]
Ceded premiums written	$ (9,807)	$ (6,997)
Ceded premiums earned	(12,430)	(8,690)
Third-Party Reinsurers
Ceded Credit Risk [Line Items]
Ceded risk-in-force	4,534,353	3,304,335
Ceded premiums written	(18,845)	(14,525)
Ceded premiums earned	(21,468)	(16,218)
Ceded claims and claim expenses	899	543
Ceding commission written	3,771	2,905
Ceding commission earned	4,206	3,151
Profit commission	$ 12,061	$ 9,201

Reserves for Insurance Claims_3

Reserves for Insurance Claims and Claim Expenses - Narrative (Details) $ in Thousands	3 Months Ended
	Mar. 31, 2019USD ($)loanclaim	Mar. 31, 2018USD ($)	Dec. 31, 2018USD ($)	Dec. 31, 2017USD ($)
Liability for Claims and Claims Adjustment Expense [Line Items]
IBNR, default period (at least)	60 days
Total gross liability for unpaid claims and claim adjustment expenses	$ 15,537	$ 10,391	$ 12,811	$ 8,761
Primary loans in default | loan	940
Number of claims paid | claim	37
Claims paid, including amounts covered by insurance	$ 900
Favorable prior year development	1,166	$ 371
Reserve for prior year insurance claims and claim expenses	$ 10,400
Fannie Mae
Liability for Claims and Claims Adjustment Expense [Line Items]
Number of loans in pool past due 60 days or more | loan	53
Risk-in-Force of loans in pool past due 60 days or more	$ 3,300
Loan-to-value ratio (less than)	0.8
Claims applied to pool deductible	$ 600
Deductible on policy	$ 9,700
QSR Transactions
Liability for Claims and Claims Adjustment Expense [Line Items]
Number of covered claims included in number of claims paid | claim	36
Component of claims paid covered under QSR Transaction	$ 200
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	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Liability for Unpaid Claims and Claims Adjustment Expense [Roll Forward]
Beginning balance	$ 12,811	$ 8,761
Less reinsurance recoverables	3,001	1,902
Beginning balance, net of reinsurance recoverables	9,810	6,859
Claims incurred:
Current year	3,909	1,940
Prior years	(1,166)	(371)
Total claims and claim expenses incurred	2,743	1,569
Claims and claim expenses paid:
Current year	0	0
Prior years	694	371
Total claims and claim expenses paid	694	371
Ending balance, net of reinsurance recoverables	11,859	8,057
Add reinsurance recoverables	3,678	2,334
Ending balance	$ 15,537	$ 10,391

Earnings per Share (EPS) - Comp

Earnings per Share (EPS) - Computation of Basic and Diluted Earnings per Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Earnings per Share, Basic [Abstract]
Net income	$ 32,899	$ 22,355
Basic weighted average shares outstanding (in shares)	66,692	62,099
Basic earnings per share (in dollars per share)	$ 0.49	$ 0.36
Earnings per Share, Diluted [Abstract]
Net income	$ 32,899	$ 22,355
Warrant gain, net of tax	0	(332)
Diluted net income	$ 32,899	$ 22,023
Basic weighted average shares outstanding (in shares)	66,692	62,099
Dilutive effect of issuable shares (in shares)	2,304	3,598
Dilutive weighted average shares outstanding (in shares)	68,996	65,697
Diluted earnings per share (in dollars per share)	$ 0.48	$ 0.34
Antidilutive securities excluded from EPS calculation (in shares)	754	169

Warrants - Narrative (Details)

Warrants - Narrative (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		12 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Dec. 31, 2018	Apr. 30, 2012
Debt Disclosure [Abstract]
Warrants issued (in shares)				992,000
Right to purchase, number of shares per warrant				1
Exercise price of warrants (in dollars per warrant)				$ 10
Warrant liability, at fair value	$ 11,831		$ 7,296	$ 5,100
Warrants exercised (in shares)	67,000	54,000
Stock issued upon exercise of warrants (in shares)	39,195	25,686
Fair value of warrant liability reclassified to additional paid in capital upon exercise		$ (500)	(900)
Change in fair value of warrant liability in current period		$ (100)	$ (300)

Income Taxes - Narrative (Detai

Income Taxes - Narrative (Details)	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Income Tax Disclosure [Abstract]
Effective income tax rate on pre-tax income or loss	15.60%	15.70%

Leases - Narrative (Details)

Leases - Narrative (Details) $ in Thousands	3 Months Ended
	Mar. 31, 2019USD ($)
Lessee, Lease, Description [Line Items]
Right-of-use assets	$ 7,700
Lease liabilities	8,871
Right-of-use assets obtained in exchange for new operating lease liabilities	8,100
Cash paid for amounts included in the measurement of operating lease liabilities	600
Operating lease expense	$ 600
Minimum
Lessee, Lease, Description [Line Items]
Operating lease terms	3 years
Maximum
Lessee, Lease, Description [Line Items]
Operating lease terms	5 years
Corporate Headquarters
Lessee, Lease, Description [Line Items]
Operating lease option to renew, term	5 years

Leases - Right-of-Use Asset and

Leases - Right-of-Use Asset and Lease Liability Assumptions (Details)	Mar. 31, 2019
Leases [Abstract]
Weighted-average remaining lease term (in years)	4 years
Weighted-average discount rate (percent)	6.21%

Leases - Future Payment Due Und

Leases - Future Payment Due Under Operating Leases (Details) $ in Thousands	Mar. 31, 2019USD ($)
Future Payment Due Under Operating Leases
2019	$ 1,853
2020	2,537
2021	2,609
2022	2,574
2023	462
Total undiscounted lease payments	10,035
Less effects of discounting	(1,164)
Present value of lease payments	$ 8,871

Leases - Future Minimum Lease P

Leases - Future Minimum Lease Payments as Accounted for Prior to Adoption of ASU 2016-02 (Details) $ in Thousands	Dec. 31, 2018USD ($)
Future Minimum Lease Payments as Accounted for Prior to Adoption of ASU 2016-02
2019	$ 2,346
2020	2,417
2021	2,489
2022	2,564
2023	463
Totals	$ 10,279

Regulatory Information - Statut

Regulatory Information - Statutory Net Income (Loss) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Combined
Statutory Accounting Practices [Line Items]
Statutory net income (loss)	$ (927)	$ (6,814)

Regulatory Information - Schedu

Regulatory Information - Schedule of Statutory Surplus, Contingency Reserve and RTC Ratio (Details) - Combined $ in Thousands	Mar. 31, 2019USD ($)	Dec. 31, 2018USD ($)
Statutory Accounting Practices [Line Items]
Statutory surplus	$ 431,824	$ 430,785
Contingency reserve	$ 375,823	$ 332,702
RTC Ratio	14	13.1

Uncategorized Items - nmih-2019

Label	Element	Value
Retained Earnings [Member]
Cumulative Effect of New Accounting Principle in Period of Adoption	us-gaap_CumulativeEffectOfNewAccountingPrincipleInPeriodOfAdoption	$ (282,000)
AOCI Attributable to Parent [Member]
Cumulative Effect of New Accounting Principle in Period of Adoption	us-gaap_CumulativeEffectOfNewAccountingPrincipleInPeriodOfAdoption	$ 282,000