NMI (NMIH) 10-Q 1 May 18 2018 Q1 Quarterly report Financial data

Document and Entity Information

Document and Entity Information - shares	3 Months Ended
	Mar. 31, 2018	Apr. 27, 2018
Document and Entity Information [Abstract]
Entity Registrant Name	NMI HOLDINGS, INC.
Entity Central Index Key	1,547,903
Document Type	10-Q
Document Period End Date	Mar. 31, 2018
Amendment Flag	false
Document Fiscal Year Focus	2,018
Document Fiscal Period Focus	Q1
Current Fiscal Year End Date	--12-31
Entity Filer Category	Accelerated Filer
Entity Common Stock, Shares Outstanding		65,573,093

CONDENSED CONSOLIDATED BALANCE

CONDENSED CONSOLIDATED BALANCE SHEETS (UNAUDITED) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Assets
Fixed maturities, available-for-sale, at fair value (amortized cost of $733,153 and $713,859 as of March 31, 2018 and December 31, 2017, respectively)	$ 723,790	$ 715,875
Cash and cash equivalents	101,890	19,196
Premiums receivable	28,164	25,179
Accrued investment income	4,765	4,212
Prepaid expenses	3,602	2,151
Deferred policy acquisition costs, net	40,026	37,925
Software and equipment, net	22,857	22,802
Intangible assets and goodwill	3,634	3,634
Prepaid reinsurance premiums	38,557	40,250
Deferred tax asset, net	16,343	19,929
Other assets	3,963	3,695
Total assets	987,591	894,848
Liabilities
Term loan	143,868	143,882
Unearned premiums	165,590	163,166
Accounts payable and accrued expenses	21,218	23,364
Reserve for insurance claims and claim expenses	10,391	8,761
Reinsurance funds withheld	33,179	34,102
Deferred ceding commission	4,838	5,024
Warrant liability, at fair value	6,563	7,472
Total liabilities	385,647	385,771
Commitments and contingencies
Shareholders' Equity
Common stock - class A shares, $0.01 par value; 65,569,342 and 60,517,512 shares issued and outstanding as of March 31, 2018 and December 31, 2017, respectively (250,000,000 shares authorized)	656	605
Additional paid-in capital	666,905	585,488
Accumulated other comprehensive loss, net of tax	(13,533)	(2,859)
Accumulated deficit	(52,084)	(74,157)
Total shareholders' equity	601,944	509,077
Total liabilities and shareholders' equity	$ 987,591	$ 894,848

CONDENSED CONSOLIDATED BALANCE3

CONDENSED CONSOLIDATED BALANCE SHEETS (UNAUDITED) (Parenthetical) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Statement of Financial Position [Abstract]
Fixed maturities, available-for-sale, amortized cost	$ 733,513	$ 713,859
Common stock, par value (in dollars per share)	$ 0.01	$ 0.01
Common stock, issued (in shares)	65,569,342	60,517,512
Common stock, outstanding (in shares)	65,569,342	60,517,512
Common stock, authorized (in shares)	250,000,000	250,000,000

CONDENSED CONSOLIDATED STATEMEN

CONDENSED CONSOLIDATED STATEMENTS OF OPERATIONS AND COMPREHENSIVE INCOME (UNAUDITED) - USD ($) shares in Thousands, $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Revenues
Net premiums earned	$ 54,914	$ 33,225
Net investment income	4,574	3,807
Net realized investment losses	0	(58)
Other revenues	64	80
Total revenues	59,552	37,054
Expenses
Insurance claims and claim expenses	1,569	635
Underwriting and operating expenses	28,453	25,989
Total expenses	30,022	26,624
Other expense
Gain (Loss) from change in fair value of warrant liability	420	(196)
Interest expense	(3,419)	(3,494)
Total other expense	(2,999)	(3,690)
Income before income taxes	26,531	6,740
Income tax expense	4,176	1,248
Net income	$ 22,355	$ 5,492
Earnings per share
Basic earnings per share (in dollars per share)	$ 0.36	$ 0.09
Diluted earnings per share (in dollars per share)	$ 0.34	$ 0.09
Weighted average common shares outstanding
Basic weighted average shares outstanding (in shares)	62,099	59,184
Dilutive weighted average shares outstanding (in shares)	65,697	62,339
Other comprehensive income (loss), net of tax:
Net unrealized (losses) gains in accumulated other comprehensive income, net of tax benefit of $423 and tax expense $664 for the quarters ended March 31, 2018 and 2017, respectively	$ (10,956)	$ 1,175
Reclassification adjustment for realized losses included in net income, net of tax expenses of $0 for the quarters ended March 31, 2018 and 2017, respectively	0	58
Other comprehensive income (loss), net of tax	(10,956)	1,233
Comprehensive income	$ 11,399	$ 6,725

CONDENSED CONSOLIDATED STATEME5

CONDENSED CONSOLIDATED STATEMENTS OF OPERATIONS AND COMPREHENSIVE INCOME (UNAUDITED) (Parenthetical) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Income Statement [Abstract]
Net unrealized (losses) gains in accumulated other comprehensive income, tax (benefit) expense	$ (423)	$ 664
Reclassification adjustment for realized losses included in net income, tax expense	$ 0	$ 0

CONDENSED CONSOLIDATED STATEME6

CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS (UNAUDITED) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Cash flows from operating activities
Net income	$ 22,355	$ 5,492
Adjustments to reconcile net income to net cash provided by (used in) operating activities:
Net realized investment losses	0	58
(Gain) Loss from change in fair value of warrant liability	(420)	196
Depreciation and amortization	1,858	1,502
Net amortization of premium on investment securities	439	357
Amortization of debt discount and debt issuance costs	361	403
Share-based compensation expense	2,805	1,911
Deferred income taxes	4,009	1,146
Changes in operating assets and liabilities:
Premiums receivable	(2,985)	(1,838)
Accrued investment income	(553)	(479)
Prepaid expenses	(1,451)	(944)
Deferred policy acquisition costs, net	(2,101)	(2,056)
Other assets	(268)	(192)
Unearned premiums	2,424	1,805
Reserve for insurance claims and claim expenses	1,630	760
Reinsurance balances, net	584	141
Accounts payable and accrued expenses	(7,556)	(10,351)
Net cash provided by (used in) operating activities	21,131	(2,089)
Cash flows from investing activities
Purchase of short-term investments	(16,858)	(38,663)
Purchase of fixed-maturity investments, available-for-sale	(74,095)	(60,212)
Proceeds from maturity of short-term investments	31,309	46,845
Proceeds from redemptions, maturities and sale of fixed-maturity investments, available-for-sale	44,444	23,841
Additions to software and equipment	(1,370)	(3,069)
Net cash used in investing activities	(16,570)	(31,258)
Cash flows from financing activities
Proceeds from issuance of common stock related to public offering	79,249	0
Proceeds from issuance of common stock related to employee equity plans	4,782	2,392
Taxes paid related to net share settlement of equity awards	(5,523)	(3,503)
Repayments of term loan	(375)	(375)
Payments of debt modification costs	0	(370)
Net cash provided by (used in) financing activities	78,133	(1,856)
Net increase (decrease) in cash and cash equivalents	82,694	(35,203)
Cash and cash equivalents, beginning of period	19,196	47,746
Cash and cash equivalents, end of period	101,890	12,543
Supplemental disclosures of cash flow information
Interest paid	3,072	3,314
Income taxes paid	$ 0	$ 170

CONDENSED CONSOLIDATED STATEME7

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)	Accumulated Deficit
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Cumulative effect of change in accounting principle		$ 903			$ 388		$ 515
Beginning balance at Dec. 31, 2016		475,509	$ 591		576,927	$ (5,287)	(96,722)
Beginning balance (in shares) at Dec. 31, 2016			59,145,000
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Common stock: class A shares issued related to warrants	[1]	$ 183			183
Common stock: class A shares issued related to warrants (in shares)		32,368	32,000	[1]
Common stock: class A shares issued under stock plans, net of shares withheld for employee taxes		$ (1,480)	$ 14		(1,494)
Common stock: class A shares issued under stock plans, net of shares withheld for employee taxes (in shares)			1,341,000
Share-based compensation expense		9,484			9,484
Change in unrealized investment gains/losses, net of tax		2,428				2,428
Net income		22,050					22,050
Ending balance at Dec. 31, 2017		509,077	$ 605		585,488	(2,859)	(74,157)
Ending balance (in shares) at Dec. 31, 2017			60,518,000
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Cumulative effect of change in accounting principle		0				282	(282)
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	25,686	[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
[1]	During the year ended December 31, 2017 and the three months ended March 31, 2018, we issued 32,368 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 STATEME8

CONDENSED CONSOLIDATED STATEMENTS OF CHANGES IN SHAREHOLDERS' EQUITY (UNAUDITED) (Parenthetical) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Mar. 31, 2018	Dec. 31, 2017
Statement of Stockholders' Equity [Abstract]
Change in unrealized investment gains/losses, tax (benefit) expense	$ (423)	$ 1,307
Stock issued upon exercise of warrants (in shares)	25,686	32,368
Common stock, par value (in dollars per share)	$ 0.01	$ 0.01

Organization, Basis of Presenta

Organization, Basis of Presentation and Summary of Accounting Principles	3 Months Ended
	Mar. 31, 2018
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). In April 2012, we completed a private placement of our securities, through which we offered and sold an aggregate of 55,000,000 of our Class A common stock resulting in net proceeds of approximately $510 million (the Private Placement), and we completed the acquisition of our insurance subsidiaries for $8.5 million in cash, common stock and warrants, plus the assumption of $1.3 million in liabilities. In November 2013, we completed an initial public offering of 2.4 million shares of our common stock, and our common stock began trading on the NASDAQ exchange on November 8, 2013, under the symbol "NMIH." In March 2018, we completed the sale of an additional 4.3 million shares of common stock including a 15% option to purchase additional shares, which was exercised in full. 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, 2017 , included in our 2017 10-K. All intercompany transactions have been eliminated. The preparation of financial statements in accordance with GAAP requires management to make estimates and assumptions that affect reported amounts of assets and liabilities, as well as disclosure of contingent assets and liabilities as of the balance sheet date. Estimates also affect the reported amounts of income and expenses for the reporting period. Actual results could differ from those estimates. The results of operations for the interim period may not be indicative of the results that may be expected for the full year ending December 31, 2018 . 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 2017 Form 10-K, other than as noted in " Reinsurance " and " Recent Accounting Pronouncements - Adopted" below. Reinsurance We account for premiums, claims and claim expenses that are ceded to reinsurers on a basis consistent with those we use to account for the original policies we issue and pursuant to the terms of our reinsurance contracts. We account for premiums ceded or otherwise paid to reinsurers as reductions to premium revenue. Effective January 1, 2018, NMIC entered into a second quota share reinsurance transaction (2018 QSR Transaction) which is similar in nature to the quota share reinsurance transaction we entered into in September 2016 (2016 QSR Transaction, together with 2018 QSR Transaction, the QSR Transactions) (see Note 5, " Reinsurance "). We earn profit and ceding commissions in connection with the QSR Transactions. Profit commissions represent a percentage of the profits recognized by reinsurers that are returned to us, based on the level of claims and claim expenses that we cede. We recognize any profit commissions we earn as increases to premium revenue. Ceding commissions are calculated as a percentage of ceded written premiums under the 2016 QSR Transaction and as a percentage of ceded earned premiums under the 2018 QSR Transaction, and we intended to cover our costs to acquire and service the direct policies. We earn the ceding commissions in a manner consistent with our recognition of earnings on the underlying insurance policies, over the terms of the policies reinsured. We account for ceding commissions earned as a reduction to underwriting and operating expenses. Under the QSR Transactions, we cede a portion of claims and claim expenses reserves to our reinsurers, which are accounted for as reinsurance recoverables in "Other Assets" on the consolidated balance sheets and as reductions to claim expense on the consolidated statements of operations. We remain directly liable for all loss payments in the event we are unable to collect from any reinsurer. Recent Accounting Pronouncements - Adopted In May 2014, the Financial Accounting Standards Board (FASB) issued Accounting Standards Update (ASU) 2014-09, Revenue from Contracts with Customers (Topic 606). This update is intended to provide a consistent approach in recognizing revenue. In December 2016, the FASB clarified that all contracts that are within the scope of Topic 944, Financial Services-Insurance , are excluded from the scope of ASU 2014-09. Accordingly, this update did not impact the recognition of revenue related to insurance premiums or investment income, which represent a majority of our total revenues. The update impacted our loan review services revenue, which is the only revenue stream in scope of the update. We adopted this update on January 1, 2018 using the modified-retrospective approach. For the period ended March 31, 2018, the impact was immaterial to our consolidated financial statements. In January 2016, the FASB issued ASU 2016-01, Financial Instruments - Overall: Recognition and Measurement of Financial Assets and Financial Liabilities (Subtopic 825-10). This update requires entities to reduce the carrying amount of deferred tax assets, if necessary, by the amount of any tax benefit that is not expected to be realized. We adopted this update effective January 1, 2018. The impact was immaterial to our consolidated financial statements. In March 2017, the FASB issued ASU 2017-08, Receivables - Nonrefundable Fees and Other Costs (Subtopic 310-20). This update shortened the amortization period for the premium on certain purchased callable debt securities to the earliest call date. The standard took effect for public business entities for fiscal years beginning after December 15, 2017. The adoption of this update had no impact on our consolidated financial statements. In February 2018, the FASB issued ASU 2018-02, Reclassification of Ce rtain Tax Effects from Accumulated Other Comprehensive Income (Topic 220). This update permits a company to reclassify the disproportionate income tax effects as a result of the 2017 Tax Cuts and Jobs Act (the TCJA) on items within accumulated other comprehensive income (AOCI) to retained earnings. This standard will take effect for public business entities for fiscal years, and interim periods within those fiscal years, beginning after December 15, 2018. Early adoption is permitted. We adopted this update on January 1, 2018 and adjusted the disproportionate incom e tax effects, or "stranded tax effects," resulting in a $0.3 million reduction to our beginning retained earnings as of January 1, 2018. Recent Accounting Pronouncements - Not Yet Adopted In February 2016, the FASB issued 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. For public business entities, this update is effective for annual periods beginning after December 15, 2018 and interim periods therein. Early adoption is permitted in any period. We expect to adopt this guidance on January 1, 2019. In September 2017, ASU 2017-13, added guidance from an SEC Staff Announcement, "Transition Related to Accounting Standards Update No. 2016-02." We anticipate this standard will have an impact on our financial position, primarily due to our office space operating lease, as we will be required to recognize lease assets and lease liabilities on our consolidated balance sheet. We will continue to assess the potential impacts of this standard, including the impact the adoption of this guidance will have on our results of operations or cash flows. 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 evaluating the impact the adoption of this ASU will have, if any, on our consolidated financial statements. 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. This standard will take effect for public business entities for fiscal years, and interim periods within those fiscal years, beginning after December 15, 2018. Early adoption is permitted. The guidance must be applied using a full or modified retrospective approach. 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, 2018
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 income based upon specific identification of securities sold. Fair Values and Gross Unrealized Gains and Losses on Investments Amortized Gross Unrealized Fair Gains Losses As of March 31, 2018 (In Thousands) U.S. Treasury securities and obligations of U.S. government agencies $ 57,018 $ — $ (1,807 ) $ 55,211 Municipal debt securities 89,792 155 (1,259 ) 88,688 Corporate debt securities 453,262 806 (6,883 ) 447,185 Asset-backed securities 125,030 357 (736 ) 124,651 Total bonds 725,102 1,318 (10,685 ) 715,735 Long-term investments - other 353 — — 353 Short-term investments 7,698 4 — 7,702 Total investments $ 733,153 $ 1,322 $ (10,685 ) $ 723,790 Amortized Gross Unrealized Fair Gains Losses As of December 31, 2017 (In Thousands) U.S. Treasury securities and obligations of U.S. government agencies $ 65,669 $ — $ (981 ) $ 64,688 Municipal debt securities 89,973 534 (659 ) 89,848 Corporate debt securities 435,562 4,231 (1,958 ) 437,835 Asset-backed securities 100,153 916 (125 ) 100,944 Total bonds 691,357 5,681 (3,723 ) 693,315 Long-term investments - other 353 — — 353 Short-term investments 22,149 58 — 22,207 Total investments $ 713,859 $ 5,739 $ (3,723 ) $ 715,875 As of March 31, 2018 and December 31, 2017 , approximately $7.0 million 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, 2018 and December 31, 2017 , 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, 2018 Amortized Fair (In Thousands) Due in one year or less $ 59,804 $ 59,705 Due after one through five years 252,066 249,638 Due after five through ten years 287,110 280,837 Due after ten years 9,143 8,959 Asset-backed securities 125,030 124,651 Total investments $ 733,153 $ 723,790 As of December 31, 2017 Amortized Fair (In Thousands) Due in one year or less $ 97,406 $ 97,394 Due after one through five years 195,795 195,626 Due after five through ten years 305,798 306,930 Due after ten years 14,707 14,981 Asset-backed securities 100,153 100,944 Total investments $ 713,859 $ 715,875 Aging of Unrealized Losses As of March 31, 2018 , the investment portfolio had gross unrealized losses of $10.7 million , $3.5 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, 2018 . We based our conclusion that these investments were not other-than-temporarily impaired as of March 31, 2018 on the following facts: (i) the unrealized losses were primarily caused by interest rate movements 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, 2018 (Dollars in Thousands) U.S. Treasury securities and obligations of U.S. government agencies 12 $ 26,792 $ (994 ) 23 $ 24,960 $ (813 ) 35 $ 51,752 $ (1,807 ) Municipal debt securities 27 54,924 (691 ) 10 17,772 (568 ) 37 72,696 (1,259 ) Corporate debt securities 180 302,287 (5,000 ) 18 42,745 (1,883 ) 198 345,032 (6,883 ) Asset-backed securities 39 74,208 (497 ) 4 9,261 (239 ) 43 83,469 (736 ) Short-term investments 1 995 — — — — 1 995 — Total 259 $ 459,206 $ (7,182 ) 55 $ 94,738 $ (3,503 ) 314 $ 553,944 $ (10,685 ) 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, 2017 (Dollars in Thousands) U.S. Treasury securities and obligations of U.S. government agencies 16 $ 29,806 $ (394 ) 26 $ 34,882 $ (587 ) 42 $ 64,688 $ (981 ) Municipal debt securities 21 38,628 (264 ) 10 17,945 (395 ) 31 56,573 (659 ) Corporate debt securities 94 128,313 (829 ) 23 48,978 (1,129 ) 117 177,291 (1,958 ) Asset-backed securities 22 27,947 (63 ) 5 12,438 (62 ) 27 40,385 (125 ) Total 153 $ 224,694 $ (1,550 ) 64 $ 114,243 $ (2,173 ) 217 $ 338,937 $ (3,723 ) The following table presents the components of net investment income: For the three months ended March 31, 2018 2017 (In Thousands) Investment income $ 4,782 $ 3,993 Investment expenses (208 ) (186 ) Net investment income $ 4,574 $ 3,807 The following table presents the components of net realized investment gains (losses): For the three months ended March 31, 2018 2017 (In Thousands) Gross realized investment gains $ — $ 279 Gross realized investment losses — (337 ) Net realized investment gains (losses) $ — $ (58 ) Investment Securities - Other-than-Temporary Impairment (OTTI) For the quarter ended March 31, 2018 , we held no other-than-temporarily impaired securities. There were no credit losses recognized in earnings for which a portion of an OTTI loss was recognized in accumulated other comprehensive income. For the quarter ended March 31, 2017, we recognized OTTI losses in earnings of $144 thousand related to a single security with an unfavorable recovery forecast. The impaired security was liquidated in the second quarter of 2017.

Fair Value of Financial Instrum

Fair Value of Financial Instruments	3 Months Ended
	Mar. 31, 2018
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, 2018 (In Thousands) U.S. Treasury securities and obligations of U.S. government agencies $ 55,211 $ — $ — $ 55,211 Municipal debt securities — 88,688 — 88,688 Corporate debt securities — 447,185 — 447,185 Asset-backed securities — 124,651 — 124,651 Long-term investment – other 353 — — 353 Cash, cash equivalents and short-term investments 109,592 — — 109,592 Total assets $ 165,156 $ 660,524 $ — $ 825,680 Warrant liability — — 6,563 6,563 Total liabilities $ — $ — $ 6,563 $ 6,563 Fair Value Measurements Using Quoted Prices in Significant Other Significant Fair Value As of December 31, 2017 (In Thousands) U.S. Treasury securities and obligations of U.S. government agencies $ 59,844 $ 4,844 $ — $ 64,688 Municipal debt securities — 89,848 — 89,848 Corporate debt securities — 437,835 — 437,835 Asset-backed securities — 100,944 — 100,944 Long-term investment - other 353 — — 353 Cash, cash equivalents and short-term investments 41,403 — — 41,403 Total assets $ 101,600 $ 633,471 $ — $ 735,071 Warrant liability — — 7,472 7,472 Total liabilities $ — $ — $ 7,472 $ 7,472 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, 2018 and the year ended December 31, 2017. The following is a roll-forward of Level 3 liabilities measured at fair value: For the three months ended March 31, Warrant Liability 2018 2017 (In Thousands) Balance, January 1 $ 7,472 $ 3,367 Change in fair value of warrant liability included in earnings (420 ) 196 Issuance of common stock on warrant exercise (489 ) — Balance, March 31 $ 6,563 $ 3,563 The following table outlines the key inputs and assumptions used in the Black-Scholes option-pricing model as of the dates indicated. As of March 31, 2018 2017 Common Stock Price $ 16.55 $ 11.40 Risk free interest rate 2.37% 1.70% Expected life 2.59 years 3.92 years Expected volatility 30.1% 30.5% Dividend yield 0% 0% The changes in fair value of the warrant liability for the quarters ended March 31, 2018 and 2017 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.

Term Loan

Term Loan	3 Months Ended
	Mar. 31, 2018
Debt Disclosure [Abstract]
Term Loan	Term Loan On November 10, 2015, we entered into a credit agreement (the Credit Agreement) to obtain a $150 million three -year senior secured term loan (the Term Loan). On February 10, 2017, we amended the Credit Agreement (Amendment No. 1) to reduce the interest rate and extend the maturity date of the Term Loan from November 10, 2018 to November 10, 2019. On October 25, 2017, we further amended the Credit Agreement (Amendment No. 2) to remove a covenant that required NMIH to maintain liquidity (as defined therein) in an aggregate amount no less than all remaining interest payments due under the Term Loan. As modified by Amendment No. 2, the Credit Agreement retains a requirement that NMIH maintain liquidity in an aggregate amount no less than the sum of all remaining principal amortization payments due under the Term Loan, excluding principal scheduled to be paid on its maturity date. The amendments to the Credit Agreement have been treated as modifications. As of March 31, 2018 , the Term Loan bears interest at the Eurodollar Rate, as defined in the Credit Agreement and subject to a 1.00% floor, plus an annual margin rate of 6.75% , representing an all-in rate of 8.54% , payable monthly or quarterly based on our interest rate election. Quarterly principal payments of $375 thousand are also required. The outstanding balance of the Term Loan as of March 31, 2018 was $146.3 million . Interest expense for the Term Loan includes interest and amortization of issuance costs, modification costs and the original issue discount. Original debt issuance costs totaling $4.9 million , including $445 thousand related to Amendment No.1 and Amendment No.2 modifications and a 1% original issue discount, are being amortized to interest expense, using the effective interest method, over the contractual life of the Term Loan. As of March 31, 2018, the remaining unamortized issuance costs, modification costs and original issue discount totaled $2.4 million . For the three months ended March 31, 2018 , we recorded $3.4 million of interest expense. We are subject to various covenants under the amended Credit Agreement, which include, but are not limited to the following: a maximum debt-to-total capitalization ratio (as defined therein) of 35% , maximum risk-to-capital (RTC) ratio of 22.0 :1.0, minimum liquidity (as defined therein) of $2.3 million as of March 31, 2018 , compliance with the PMIERs financial requirements (subject to any GSE-approved waivers), and minimum shareholders' equity requirements. This description is not intended to be complete in all respects and is qualified in its entirety by the terms of the amended Credit Agreement, including its covenants and events of default. We were in compliance with all covenants as of March 31, 2018 . Future principal payments for the Term Loan as of March 31, 2018 are as follows: As of March 31, 2018 Principal (In thousands) 2018 1,125 2019 145,125 Total $ 146,250

Reinsurance

Reinsurance	3 Months Ended
	Mar. 31, 2018
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, 2018 March 31, 2017 (In Thousands) Net premiums written Direct $ 66,027 $ 39,245 Ceded (1) (6,997 ) (4,641 ) Net premiums written $ 59,030 $ 34,604 Net premiums earned Direct $ 63,604 $ 37,438 Ceded (1) (8,690 ) (4,213 ) Net premiums earned $ 54,914 $ 33,225 (1) Net of profit commission Excess-of-loss reinsurance In May 2017, NMIC entered into a reinsurance agreement with Oaktown Re Ltd. (Oaktown Re) that 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 will retain the first layer of $126.8 million of aggregate losses and Oaktown Re will then provide second layer coverage up to the outstanding reinsurance coverage amount. NMIC will then retain losses in excess of the outstanding reinsurance coverage amount. The outstanding reinsurance coverage amount decreases from $211.3 million at inception over a ten -year period as the underlying covered mortgages amortize and/or are repaid and was $166.6 million as of March 31, 2018 . 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 Notes). The Notes mature on April 26, 2027. All of the proceeds paid to Oaktown Re from the sale of the Notes were deposited into a reinsurance trust to collateralize and fund the obligations of Oaktown Re to NMIC under the reinsurance agreement. At all times, funds in the reinsurance trust account are required to be invested in high credit quality money market funds. We refer collectively to NMIC's reinsurance agreement with Oaktown Re and the issuance of the 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, 2018 , NMIC paid risk premiums of $1.6 million . NMIC did not cede any losses to Oaktown Re. Under the reinsurance agreement, NMIC holds an optional termination right if certain events occur, 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 the agreement. In addition, there are certain events that will result in mandatory termination of the agreement, including NMIC's failure to pay premiums or consent to reductions in the trust account to make principal payments to noteholders, among others. At the time the 2017 ILN Transaction was entered into with Oaktown Re, we evaluated the applicability of the accounting guidance that addresses VIEs. As a result of the evaluation of the 2017 ILN Transaction, we concluded that Oaktown Re is a VIE. However, given that NMIC does not have significant economic exposure in Oaktown Re, we do not consolidate Oaktown Re in our consolidated financial statements. Quota share reinsurance 2016 QSR Transaction Effective September 1, 2016, NMIC entered into 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 the 2018 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 S&P, A.M. Best or both. Under the 2018 QSR Transaction, NMIC cedes premiums earned related to 25% of risk on eligible policies written from January 1, 2018 through December 31, 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. The following table shows the amounts related to the QSR Transactions: For the three months ended March 31, 2018 March 31, 2017 (In Thousands) Ceded risk-in-force $ 3,304,335 $ 2,167,745 Ceded premiums written (1) (14,525 ) (10,292 ) Ceded premiums earned (1) (16,218 ) (9,865 ) Ceded claims and claims expenses 543 268 Ceding commission written 2,905 2,058 Ceding commission earned 3,151 2,065 Profit commission 9,201 5,651 (1) The presentation of these line items was enhanced starting in the second quarter of 2017, to separately disclose "Profit commission." Prior to the second quarter of 2017, "Profit commission" was netted within both the "Ceded premium written" and "Ceded premium earned" lines. 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 income 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 $2.3 million as of March 31, 2018 . 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 will also settle quarterly. 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. NMIC did not have any reinsurance recoverable on loss reserves related to our 2018 QSR Transaction as of March 31, 2018.

Reserves for Insurance Claims a

Reserves for Insurance Claims and Claim Expenses	3 Months Ended
	Mar. 31, 2018
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 claims 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, 2018 , we had reserves for insurance claims and claims expenses of $10.4 million for 1,000 primary loans in default. During the first three months of 2018, we paid 17 claims totaling $482 thousand , including 14 claims covered under the QSR Transactions representing $111 thousand of ceded claims and claims 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, 2018 , 64 loans in the pool were past due by 60 days or more. These 64 loans represent approximately $4.2 million of risk-in-force (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, 2018 and the expected severity (all loans in the pool have loan-to-value ratios (LTV) ratios under 80% ), we did not have any case or IBNR reserves for pool risks at March 31, 2018 or March 31, 2017 . In connection with the settlement of pool claims, we applied $492 thousand to the pool deductible through March 31, 2018 . At March 31, 2018 , the remaining pool deductible was $9.9 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, 2018 2017 (In Thousands) Beginning balance $ 8,761 $ 3,001 Less reinsurance recoverables (1) (1,902 ) (297 ) Beginning balance, net of reinsurance recoverables 6,859 2,704 Add claims incurred: Claims and claim expenses incurred: Current year (2) 1,940 955 Prior years (3) (371 ) (320 ) Total claims and claims expenses incurred 1,569 635 Less claims paid: Claims and claim expenses paid: Current year (2) — — Prior years (3) 371 142 Total claims and claim expenses paid 371 142 Reserve at end of period, net of reinsurance recoverables 8,057 3,197 Add reinsurance recoverables (1) 2,334 564 Ending balance $ 10,391 $ 3,761 (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. (3) Related to insured loans with defaults occurring in prior years, which have been continuously in default since that time. The "claims incurred" section of the table above shows claims and claim expenses incurred on NODs for current and prior years, including IBNR reserves. The amount of claims incurred relating to current year NODs represents the estimated amount of claims and claims expenses to be ultimately paid on such loans in default. We recognized $371 thousand and $320 thousand of favorable prior year development during the three months ended March 31, 2018 and 2017, 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 $7.2 million related to prior year defaults remained as of March 31, 2018 .

Earnings per Share (EPS)

Earnings per Share (EPS)	3 Months Ended
	Mar. 31, 2018
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, while 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 RSUs, and exercise of vested and unvested stock options and outstanding warrants. 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, 2018 2017 (In Thousands, except for per share data) Basic net income $ 22,355 $ 5,492 Basic weighted average shares outstanding 62,099 59,184 Basic earnings per share $ 0.36 $ 0.09 Basic net income $ 22,355 $ 5,492 Warrant gain, net of tax $ (332 ) $ — Diluted net income $ 22,023 $ 5,492 Basic weighted average shares outstanding 62,099 59,184 Dilutive effect of issuable shares 3,598 3,155 Diluted weighted average shares outstanding 65,697 62,339 Diluted earnings per share $ 0.34 $ 0.09 Anti-dilutive securities 169 1,211

Warrants

Warrants	3 Months Ended
	Mar. 31, 2018
Debt Disclosure [Abstract]
Warrants	Warrants We issued 992 thousand warrants in connection with the Private Placement. 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, 2018, 54 thousand warrants were exercised resulting in 26 thousand common shares issued. No warrants were exercised during the three months ended March 31, 2017. Upon exercise, we reclassified the fair value of the warrants from warrant liability to additional paid-in capital and recognized a loss of approximately $52 thousand . 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, 2018
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% for the current and all future years following the enactment of the TCJA on December 22, 2017. We were subject to a statutory U.S. federal corporate income tax rate of 35% for all prior years through December 31, 2017. 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 15.7% for the three months ended March 31, 2018 , compared to 18.5% for the three months ended March 31, 2017 . The decrease in the effective tax rate for the three months ended March 31, 2018 compared to the three months ended March 31, 2017 is attributable to the decrease in the statutory U.S. federal corporate income tax rate. We currently pay no federal income tax primarily due to the forecasted utilization of our federal net operating loss carryforwards, which were $93.3 million as of December 31, 2017. As a result, the interim provision for income taxes represents changes to deferred tax assets. Provisional amounts The TCJA reduced the statutory U.S. federal corporate income tax rate from 35% to 21% and changed the tax deductibility of certain expenses for tax years beginning after December 31, 2017. We have not completed our full assessment of the tax effects of the enactment of the TCJA on our deferred tax balances as of March 31, 2018 and December 31, 2017; however, in certain cases, as described below, we have made reasonable estimates of the effects on our deferred tax balances. We recognized a $13.6 million income tax expense in the year ended December 31, 2017 for the items we could reasonably estimate. We are still analyzing the TCJA and refining our calculations, which could impact the measurement of our existing deferred tax assets including those related to share-based compensation. For tax years beginning after December 31, 2017, the TCJA expanded the number of individuals whose compensation is subject to a $1 million cap on tax deductibility and includes performance-based compensation in the calculation. As a result, we recorded a provisional amount to reduce the future tax benefit related to share-based compensation. We will continue to make and refine our calculations as additional analysis is completed. In addition, our estimates may also be affected as we incorporate additional guidance that may be issued by the U.S. Treasury Department, the IRS, or other standard-setting bodies. In February 2018, the FASB issued ASU 2018-02, Reclassification of Ce rtain Tax Effects from Accumulated Other Comprehensive Income (Topic 220). This update permits a company to reclassify the disproportionate income tax effects as a result of the TCJA on items within AOCI to retained earnings. We adopted this update on January 1, 2018 and adjusted the disproportionate incom e tax effects, or "stranded tax effects," resulting in a $0.3 million reduction to our beginning retained earnings as of January 1, 2018. The disproportionate tax effects that remain in AOCI of $4.2 million was not related to the TCJA and will remain in AOCI until certain events occur. Our elected accounting policy for available-for-sale debt securities is the "aggregate portfolio" approach.

Common Stock Offerings

Common Stock Offerings	3 Months Ended
	Mar. 31, 2018
Equity [Abstract]
Common Stock Offerings	Common Stock Offerings In March 2018, we completed the sale of 3.7 million shares of common stock and granted the underwriters on the transaction a 15% overallotment option to purchase additional shares. The overallotment option was exercised in full, resulting in a total of 4.3 million shares of common stock issued. The common stock offering generated total proceeds of approximately $79.2 million , net of underwriting discounts, commissions and other direct offering expenses.

Regulatory Information

Regulatory Information	3 Months Ended
	Mar. 31, 2018
Insurance [Abstract]
Regulatory Information	Regulatory Information 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 loss was as follows: For the three months ended March 31, 2018 2017 (In Thousands) Statutory net loss $ (6,814 ) $ (10,090 ) NMIC and Re One's statutory surplus, contingency reserve and risk to capital (RTC) ratios were as follows: March 31, 2018 December 31, 2017 ($ In Thousands) Statutory surplus $ 368,202 $ 371,084 Contingency reserve 218,518 186,641 Risk-to-Capital 14.4:1 13.2:1 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 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.

Subsequent Event

Subsequent Event	3 Months Ended
	Mar. 31, 2018
Subsequent Events [Abstract]
Subsequent Event	Subsequent Event In April 2018, NMIH made a capital contribution of $70 million to NMIC.

Organization, Basis of Presen21

Organization, Basis of Presentation and Summary of Accounting Principles (Policies)	3 Months Ended
	Mar. 31, 2018
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, 2017 , included in our 2017 10-K. All intercompany transactions have been eliminated. The preparation of financial statements in accordance with GAAP requires management to make estimates and assumptions that affect reported amounts of assets and liabilities, as well as disclosure of contingent assets and liabilities as of the balance sheet date. Estimates also affect the reported amounts of income and expenses for the reporting period. Actual results could differ from those estimates. The results of operations for the interim period may not be indicative of the results that may be expected for the full year ending December 31, 2018 .
Reinsurance	Reinsurance We account for premiums, claims and claim expenses that are ceded to reinsurers on a basis consistent with those we use to account for the original policies we issue and pursuant to the terms of our reinsurance contracts. We account for premiums ceded or otherwise paid to reinsurers as reductions to premium revenue. Effective January 1, 2018, NMIC entered into a second quota share reinsurance transaction (2018 QSR Transaction) which is similar in nature to the quota share reinsurance transaction we entered into in September 2016 (2016 QSR Transaction, together with 2018 QSR Transaction, the QSR Transactions) (see Note 5, " Reinsurance "). We earn profit and ceding commissions in connection with the QSR Transactions. Profit commissions represent a percentage of the profits recognized by reinsurers that are returned to us, based on the level of claims and claim expenses that we cede. We recognize any profit commissions we earn as increases to premium revenue. Ceding commissions are calculated as a percentage of ceded written premiums under the 2016 QSR Transaction and as a percentage of ceded earned premiums under the 2018 QSR Transaction, and we intended to cover our costs to acquire and service the direct policies. We earn the ceding commissions in a manner consistent with our recognition of earnings on the underlying insurance policies, over the terms of the policies reinsured. We account for ceding commissions earned as a reduction to underwriting and operating expenses. Under the QSR Transactions, we cede a portion of claims and claim expenses reserves to our reinsurers, which are accounted for as reinsurance recoverables in "Other Assets" on the consolidated balance sheets and as reductions to claim expense on the consolidated statements of operations. We remain directly liable for all loss payments in the event we are unable to collect from any reinsurer.
Recent Accounting Pronouncements	Recent Accounting Pronouncements - Adopted In May 2014, the Financial Accounting Standards Board (FASB) issued Accounting Standards Update (ASU) 2014-09, Revenue from Contracts with Customers (Topic 606). This update is intended to provide a consistent approach in recognizing revenue. In December 2016, the FASB clarified that all contracts that are within the scope of Topic 944, Financial Services-Insurance , are excluded from the scope of ASU 2014-09. Accordingly, this update did not impact the recognition of revenue related to insurance premiums or investment income, which represent a majority of our total revenues. The update impacted our loan review services revenue, which is the only revenue stream in scope of the update. We adopted this update on January 1, 2018 using the modified-retrospective approach. For the period ended March 31, 2018, the impact was immaterial to our consolidated financial statements. In January 2016, the FASB issued ASU 2016-01, Financial Instruments - Overall: Recognition and Measurement of Financial Assets and Financial Liabilities (Subtopic 825-10). This update requires entities to reduce the carrying amount of deferred tax assets, if necessary, by the amount of any tax benefit that is not expected to be realized. We adopted this update effective January 1, 2018. The impact was immaterial to our consolidated financial statements. In March 2017, the FASB issued ASU 2017-08, Receivables - Nonrefundable Fees and Other Costs (Subtopic 310-20). This update shortened the amortization period for the premium on certain purchased callable debt securities to the earliest call date. The standard took effect for public business entities for fiscal years beginning after December 15, 2017. The adoption of this update had no impact on our consolidated financial statements. In February 2018, the FASB issued ASU 2018-02, Reclassification of Ce rtain Tax Effects from Accumulated Other Comprehensive Income (Topic 220). This update permits a company to reclassify the disproportionate income tax effects as a result of the 2017 Tax Cuts and Jobs Act (the TCJA) on items within accumulated other comprehensive income (AOCI) to retained earnings. This standard will take effect for public business entities for fiscal years, and interim periods within those fiscal years, beginning after December 15, 2018. Early adoption is permitted. We adopted this update on January 1, 2018 and adjusted the disproportionate incom e tax effects, or "stranded tax effects," resulting in a $0.3 million reduction to our beginning retained earnings as of January 1, 2018. Recent Accounting Pronouncements - Not Yet Adopted In February 2016, the FASB issued 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. For public business entities, this update is effective for annual periods beginning after December 15, 2018 and interim periods therein. Early adoption is permitted in any period. We expect to adopt this guidance on January 1, 2019. In September 2017, ASU 2017-13, added guidance from an SEC Staff Announcement, "Transition Related to Accounting Standards Update No. 2016-02." We anticipate this standard will have an impact on our financial position, primarily due to our office space operating lease, as we will be required to recognize lease assets and lease liabilities on our consolidated balance sheet. We will continue to assess the potential impacts of this standard, including the impact the adoption of this guidance will have on our results of operations or cash flows. 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 evaluating the impact the adoption of this ASU will have, if any, on our consolidated financial statements. 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. This standard will take effect for public business entities for fiscal years, and interim periods within those fiscal years, beginning after December 15, 2018. Early adoption is permitted. The guidance must be applied using a full or modified retrospective approach. 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, while 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 RSUs, and exercise of vested and unvested stock options and outstanding warrants.

Investments (Tables)

Investments (Tables)	3 Months Ended
	Mar. 31, 2018
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, 2018 (In Thousands) U.S. Treasury securities and obligations of U.S. government agencies $ 57,018 $ — $ (1,807 ) $ 55,211 Municipal debt securities 89,792 155 (1,259 ) 88,688 Corporate debt securities 453,262 806 (6,883 ) 447,185 Asset-backed securities 125,030 357 (736 ) 124,651 Total bonds 725,102 1,318 (10,685 ) 715,735 Long-term investments - other 353 — — 353 Short-term investments 7,698 4 — 7,702 Total investments $ 733,153 $ 1,322 $ (10,685 ) $ 723,790 Amortized Gross Unrealized Fair Gains Losses As of December 31, 2017 (In Thousands) U.S. Treasury securities and obligations of U.S. government agencies $ 65,669 $ — $ (981 ) $ 64,688 Municipal debt securities 89,973 534 (659 ) 89,848 Corporate debt securities 435,562 4,231 (1,958 ) 437,835 Asset-backed securities 100,153 916 (125 ) 100,944 Total bonds 691,357 5,681 (3,723 ) 693,315 Long-term investments - other 353 — — 353 Short-term investments 22,149 58 — 22,207 Total investments $ 713,859 $ 5,739 $ (3,723 ) $ 715,875
Schedule of Investments by Maturity	The amortized cost and fair values of available-for-sale securities as of March 31, 2018 and December 31, 2017 , 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, 2018 Amortized Fair (In Thousands) Due in one year or less $ 59,804 $ 59,705 Due after one through five years 252,066 249,638 Due after five through ten years 287,110 280,837 Due after ten years 9,143 8,959 Asset-backed securities 125,030 124,651 Total investments $ 733,153 $ 723,790 As of December 31, 2017 Amortized Fair (In Thousands) Due in one year or less $ 97,406 $ 97,394 Due after one through five years 195,795 195,626 Due after five through ten years 305,798 306,930 Due after ten years 14,707 14,981 Asset-backed securities 100,153 100,944 Total investments $ 713,859 $ 715,875
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, 2018 (Dollars in Thousands) U.S. Treasury securities and obligations of U.S. government agencies 12 $ 26,792 $ (994 ) 23 $ 24,960 $ (813 ) 35 $ 51,752 $ (1,807 ) Municipal debt securities 27 54,924 (691 ) 10 17,772 (568 ) 37 72,696 (1,259 ) Corporate debt securities 180 302,287 (5,000 ) 18 42,745 (1,883 ) 198 345,032 (6,883 ) Asset-backed securities 39 74,208 (497 ) 4 9,261 (239 ) 43 83,469 (736 ) Short-term investments 1 995 — — — — 1 995 — Total 259 $ 459,206 $ (7,182 ) 55 $ 94,738 $ (3,503 ) 314 $ 553,944 $ (10,685 ) 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, 2017 (Dollars in Thousands) U.S. Treasury securities and obligations of U.S. government agencies 16 $ 29,806 $ (394 ) 26 $ 34,882 $ (587 ) 42 $ 64,688 $ (981 ) Municipal debt securities 21 38,628 (264 ) 10 17,945 (395 ) 31 56,573 (659 ) Corporate debt securities 94 128,313 (829 ) 23 48,978 (1,129 ) 117 177,291 (1,958 ) Asset-backed securities 22 27,947 (63 ) 5 12,438 (62 ) 27 40,385 (125 ) Total 153 $ 224,694 $ (1,550 ) 64 $ 114,243 $ (2,173 ) 217 $ 338,937 $ (3,723 )
Schedule of Net Investment Income	The following table presents the components of net investment income: For the three months ended March 31, 2018 2017 (In Thousands) Investment income $ 4,782 $ 3,993 Investment expenses (208 ) (186 ) Net investment income $ 4,574 $ 3,807
Schedule of Net Realized Investment Gains (Losses)	The following table presents the components of net realized investment gains (losses): For the three months ended March 31, 2018 2017 (In Thousands) Gross realized investment gains $ — $ 279 Gross realized investment losses — (337 ) Net realized investment gains (losses) $ — $ (58 )

Fair Value of Financial Instr23

Fair Value of Financial Instruments (Tables)	3 Months Ended
	Mar. 31, 2018
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, 2018 (In Thousands) U.S. Treasury securities and obligations of U.S. government agencies $ 55,211 $ — $ — $ 55,211 Municipal debt securities — 88,688 — 88,688 Corporate debt securities — 447,185 — 447,185 Asset-backed securities — 124,651 — 124,651 Long-term investment – other 353 — — 353 Cash, cash equivalents and short-term investments 109,592 — — 109,592 Total assets $ 165,156 $ 660,524 $ — $ 825,680 Warrant liability — — 6,563 6,563 Total liabilities $ — $ — $ 6,563 $ 6,563 Fair Value Measurements Using Quoted Prices in Significant Other Significant Fair Value As of December 31, 2017 (In Thousands) U.S. Treasury securities and obligations of U.S. government agencies $ 59,844 $ 4,844 $ — $ 64,688 Municipal debt securities — 89,848 — 89,848 Corporate debt securities — 437,835 — 437,835 Asset-backed securities — 100,944 — 100,944 Long-term investment - other 353 — — 353 Cash, cash equivalents and short-term investments 41,403 — — 41,403 Total assets $ 101,600 $ 633,471 $ — $ 735,071 Warrant liability — — 7,472 7,472 Total liabilities $ — $ — $ 7,472 $ 7,472
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 2018 2017 (In Thousands) Balance, January 1 $ 7,472 $ 3,367 Change in fair value of warrant liability included in earnings (420 ) 196 Issuance of common stock on warrant exercise (489 ) — Balance, March 31 $ 6,563 $ 3,563
Schedule of Key Inputs and Assumptions in Option-Pricing Model	The following table outlines the key inputs and assumptions used in the Black-Scholes option-pricing model as of the dates indicated. As of March 31, 2018 2017 Common Stock Price $ 16.55 $ 11.40 Risk free interest rate 2.37% 1.70% Expected life 2.59 years 3.92 years Expected volatility 30.1% 30.5% Dividend yield 0% 0%

Term Loan (Tables)

Term Loan (Tables)	3 Months Ended
	Mar. 31, 2018
Debt Disclosure [Abstract]
Schedule of Future Principal Payments	Future principal payments for the Term Loan as of March 31, 2018 are as follows: As of March 31, 2018 Principal (In thousands) 2018 1,125 2019 145,125 Total $ 146,250

Reinsurance (Tables)

Reinsurance (Tables)	3 Months Ended
	Mar. 31, 2018
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, 2018 March 31, 2017 (In Thousands) Net premiums written Direct $ 66,027 $ 39,245 Ceded (1) (6,997 ) (4,641 ) Net premiums written $ 59,030 $ 34,604 Net premiums earned Direct $ 63,604 $ 37,438 Ceded (1) (8,690 ) (4,213 ) Net premiums earned $ 54,914 $ 33,225 (1) Net of profit commission The following table shows the amounts related to the QSR Transactions: For the three months ended March 31, 2018 March 31, 2017 (In Thousands) Ceded risk-in-force $ 3,304,335 $ 2,167,745 Ceded premiums written (1) (14,525 ) (10,292 ) Ceded premiums earned (1) (16,218 ) (9,865 ) Ceded claims and claims expenses 543 268 Ceding commission written 2,905 2,058 Ceding commission earned 3,151 2,065 Profit commission 9,201 5,651 (1) The presentation of these line items was enhanced starting in the second quarter of 2017, to separately disclose "Profit commission." Prior to the second quarter of 2017, "Profit commission" was netted within both the "Ceded premium written" and "Ceded premium earned" lines.

Reserves for Insurance Claims26

Reserves for Insurance Claims and Claim Expenses (Tables)	3 Months Ended
	Mar. 31, 2018
Insurance [Abstract]
Reconciliation of Liability for Insurance Claims and Claims 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, 2018 2017 (In Thousands) Beginning balance $ 8,761 $ 3,001 Less reinsurance recoverables (1) (1,902 ) (297 ) Beginning balance, net of reinsurance recoverables 6,859 2,704 Add claims incurred: Claims and claim expenses incurred: Current year (2) 1,940 955 Prior years (3) (371 ) (320 ) Total claims and claims expenses incurred 1,569 635 Less claims paid: Claims and claim expenses paid: Current year (2) — — Prior years (3) 371 142 Total claims and claim expenses paid 371 142 Reserve at end of period, net of reinsurance recoverables 8,057 3,197 Add reinsurance recoverables (1) 2,334 564 Ending balance $ 10,391 $ 3,761 (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. (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, 2018
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, 2018 2017 (In Thousands, except for per share data) Basic net income $ 22,355 $ 5,492 Basic weighted average shares outstanding 62,099 59,184 Basic earnings per share $ 0.36 $ 0.09 Basic net income $ 22,355 $ 5,492 Warrant gain, net of tax $ (332 ) $ — Diluted net income $ 22,023 $ 5,492 Basic weighted average shares outstanding 62,099 59,184 Dilutive effect of issuable shares 3,598 3,155 Diluted weighted average shares outstanding 65,697 62,339 Diluted earnings per share $ 0.34 $ 0.09 Anti-dilutive securities 169 1,211

Regulatory Information (Tables)

Regulatory Information (Tables)	3 Months Ended
	Mar. 31, 2018
Insurance [Abstract]
Schedule of Statutory Net Loss, Surplus, Contingency Reserve and Risk-to-Capital Ratio	NMIC and Re One's combined statutory net loss was as follows: For the three months ended March 31, 2018 2017 (In Thousands) Statutory net loss $ (6,814 ) $ (10,090 ) NMIC and Re One's statutory surplus, contingency reserve and risk to capital (RTC) ratios were as follows: March 31, 2018 December 31, 2017 ($ In Thousands) Statutory surplus $ 368,202 $ 371,084 Contingency reserve 218,518 186,641 Risk-to-Capital 14.4:1 13.2:1

Organization, Basis of Presen29

Organization, Basis of Presentation and Summary of Accounting Principles - Narrative (Details) $ in Millions	1 Months Ended
	Mar. 31, 2018stateshares	Nov. 30, 2013shares	Apr. 30, 2012USD ($)shares
Business Acquisition [Line Items]
Common stock offered and sold (in shares) | shares	4,300,000
Number of states in which the entity operates | state	50
Private Placement
Business Acquisition [Line Items]
Proceeds from issuance of common stock, net of stock issuance costs | $			$ 510
IPO
Business Acquisition [Line Items]
Common stock offered and sold (in shares) | shares		2,400,000
Overallotment Option
Business Acquisition [Line Items]
Overallotment option included in sale of stock (percent)	15.00%
MAC Financial Holding Corporation and Subsidiaries
Business Acquisition [Line Items]
Cash, common stock and warrants issued for acquisition | $			8.5
Liabilities assumed in acquisition | $			$ 1.3
Common Stock - Class A | Private Placement
Business Acquisition [Line Items]
Common stock offered and sold (in shares) | shares			55,000,000

Organization, Basis of Presen30

Organization, Basis of Presentation and Summary of Accounting Principles - Recent Accounting Pronouncements (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
New Accounting Pronouncements [Line Items]
Cumulative effect of change in accounting principle	$ 0	$ 903
Retained Earnings
New Accounting Pronouncements [Line Items]
Cumulative effect of change in accounting principle	(282)	$ 515
ASU No. 2018-02 | Retained Earnings
New Accounting Pronouncements [Line Items]
Cumulative effect of change in accounting principle	$ (300)

Investments - Fair Values and G

Investments - Fair Values and Gross Unrealized Gains and Losses (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	$ 733,153	$ 713,859
Gross Unrealized Gains	1,322	5,739
Gross Unrealized (Losses)	(10,685)	(3,723)
Fair Value	723,790	715,875
U.S. Treasury securities and obligations of U.S. government agencies
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	57,018	65,669
Gross Unrealized Gains	0	0
Gross Unrealized (Losses)	(1,807)	(981)
Fair Value	55,211	64,688
Municipal debt securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	89,792	89,973
Gross Unrealized Gains	155	534
Gross Unrealized (Losses)	(1,259)	(659)
Fair Value	88,688	89,848
Corporate debt securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	453,262	435,562
Gross Unrealized Gains	806	4,231
Gross Unrealized (Losses)	(6,883)	(1,958)
Fair Value	447,185	437,835
Asset-backed securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	125,030	100,153
Gross Unrealized Gains	357	916
Gross Unrealized (Losses)	(736)	(125)
Fair Value	124,651	100,944
Bonds
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	725,102	691,357
Gross Unrealized Gains	1,318	5,681
Gross Unrealized (Losses)	(10,685)	(3,723)
Fair Value	715,735	693,315
Long-term investments - other
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	353	353
Gross Unrealized Gains	0	0
Gross Unrealized (Losses)	0	0
Fair Value	353	353
Short-term investments
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	7,698	22,149
Gross Unrealized Gains	4	58
Gross Unrealized (Losses)	0	0
Fair Value	$ 7,702	$ 22,207

Investments - Scheduled Maturit

Investments - Scheduled Maturities (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Amortized Cost
Due in one year or less	$ 59,804	$ 97,406
Due after one through five years	252,066	195,795
Due after five through ten years	287,110	305,798
Due after ten years	9,143	14,707
Asset-backed securities	125,030	100,153
Amortized Cost	733,153	713,859
Fair Value
Due in one year or less	59,705	97,394
Due after one through five years	249,638	195,626
Due after five through ten years	280,837	306,930
Due after ten years	8,959	14,981
Asset-backed securities	124,651	100,944
Fair Value	$ 723,790	$ 715,875

Investments - Aging of Unrealiz

Investments - Aging of Unrealized Losses (Details) $ in Thousands	Mar. 31, 2018USD ($)security	Dec. 31, 2017USD ($)security
Schedule of Available-for-sale Securities [Line Items]
Number of securities, less than 12 months | security	259	153
Fair value, less than 12 months	$ 459,206	$ 224,694
Unrealized losses, less than 12 months	$ (7,182)	$ (1,550)
Number of securities,12 months or greater | security	55	64
Fair value, 12 months or greater	$ 94,738	$ 114,243
Unrealized losses, 12 months or greater	$ (3,503)	$ (2,173)
Number of securities, total | security	314	217
Fair value	$ 553,944	$ 338,937
Unrealized Losses	$ (10,685)	$ (3,723)
U.S. Treasury securities and obligations of U.S. government agencies
Schedule of Available-for-sale Securities [Line Items]
Number of securities, less than 12 months | security	12	16
Fair value, less than 12 months	$ 26,792	$ 29,806
Unrealized losses, less than 12 months	$ (994)	$ (394)
Number of securities,12 months or greater | security	23	26
Fair value, 12 months or greater	$ 24,960	$ 34,882
Unrealized losses, 12 months or greater	$ (813)	$ (587)
Number of securities, total | security	35	42
Fair value	$ 51,752	$ 64,688
Unrealized Losses	$ (1,807)	$ (981)
Municipal debt securities
Schedule of Available-for-sale Securities [Line Items]
Number of securities, less than 12 months | security	27	21
Fair value, less than 12 months	$ 54,924	$ 38,628
Unrealized losses, less than 12 months	$ (691)	$ (264)
Number of securities,12 months or greater | security	10	10
Fair value, 12 months or greater	$ 17,772	$ 17,945
Unrealized losses, 12 months or greater	$ (568)	$ (395)
Number of securities, total | security	37	31
Fair value	$ 72,696	$ 56,573
Unrealized Losses	$ (1,259)	$ (659)
Corporate debt securities
Schedule of Available-for-sale Securities [Line Items]
Number of securities, less than 12 months | security	180	94
Fair value, less than 12 months	$ 302,287	$ 128,313
Unrealized losses, less than 12 months	$ (5,000)	$ (829)
Number of securities,12 months or greater | security	18	23
Fair value, 12 months or greater	$ 42,745	$ 48,978
Unrealized losses, 12 months or greater	$ (1,883)	$ (1,129)
Number of securities, total | security	198	117
Fair value	$ 345,032	$ 177,291
Unrealized Losses	$ (6,883)	$ (1,958)
Asset-backed securities
Schedule of Available-for-sale Securities [Line Items]
Number of securities, less than 12 months | security	39	22
Fair value, less than 12 months	$ 74,208	$ 27,947
Unrealized losses, less than 12 months	$ (497)	$ (63)
Number of securities,12 months or greater | security	4	5
Fair value, 12 months or greater	$ 9,261	$ 12,438
Unrealized losses, 12 months or greater	$ (239)	$ (62)
Number of securities, total | security	43	27
Fair value	$ 83,469	$ 40,385
Unrealized Losses	$ (736)	$ (125)
Short-term investments
Schedule of Available-for-sale Securities [Line Items]
Number of securities, less than 12 months | security	1
Fair value, less than 12 months	$ 995
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	$ 995
Unrealized Losses	$ 0

Investments - Net Investment In

Investments - Net Investment Income (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Investment Income, Net [Abstract]
Investment income	$ 4,782	$ 3,993
Investment expenses	(208)	(186)
Net investment income	$ 4,574	$ 3,807

Investments - Net Realized Inve

Investments - Net Realized Investment Gains (Losses) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Investments, Debt and Equity Securities [Abstract]
Gross realized investment gains	$ 0	$ 279
Gross realized investment losses	0	(337)
Net realized investment gains (losses)	$ 0	$ (58)

Investments - Narrative (Detail

Investments - Narrative (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2018	Dec. 31, 2017
Schedule of Available-for-sale Securities [Line Items]
Unrealized loss position, accumulated loss		$ 10,685	$ 3,723
Unrealized loss position, 12 months or greater		3,503	2,173
Other-than-temporary impairment	$ 144
U.S. Treasury securities and obligations of U.S. government agencies
Schedule of Available-for-sale Securities [Line Items]
Cash and investments held with various state insurance departments		7,000	7,000
Unrealized loss position, accumulated loss		1,807	981
Unrealized loss position, 12 months or greater		$ 813	$ 587

Fair Value of Financial Instr37

Fair Value of Financial Instruments - Assets and Liabilities at Fair Value (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value of securities	$ 723,790	$ 715,875
Warrant liability	6,563	7,472
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	55,211	64,688
Municipal debt securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value of securities	88,688	89,848
Corporate debt securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value of securities	447,185	437,835
Asset-backed securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value of securities	124,651	100,944
Long-term investments - other
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value of securities	353	353
Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash, cash equivalents and short-term investments	109,592	41,403
Total assets	825,680	735,071
Warrant liability	6,563	7,472
Total liabilities	6,563	7,472
Fair Value, Measurements, 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	55,211	64,688
Fair Value, Measurements, Recurring | Municipal debt securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value of securities	88,688	89,848
Fair Value, Measurements, Recurring | Corporate debt securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value of securities	447,185	437,835
Fair Value, Measurements, Recurring | Asset-backed securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value of securities	124,651	100,944
Fair Value, Measurements, Recurring | Long-term investments - other
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value of securities	353	353
Fair Value, Measurements, 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	109,592	41,403
Total assets	165,156	101,600
Warrant liability	0	0
Total liabilities	0	0
Fair Value, Measurements, 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	55,211	59,844
Fair Value, Measurements, 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
Fair Value, Measurements, 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
Fair Value, Measurements, 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
Fair Value, Measurements, Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1) | Long-term investments - other
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value of securities	353	353
Fair Value, Measurements, 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	660,524	633,471
Warrant liability	0	0
Total liabilities	0	0
Fair Value, Measurements, 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	4,844
Fair Value, Measurements, 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	88,688	89,848
Fair Value, Measurements, 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	447,185	437,835
Fair Value, Measurements, 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	124,651	100,944
Fair Value, Measurements, Recurring | Significant Other Observable Inputs (Level 2) | Long-term investments - other
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value of securities	0	0
Fair Value, Measurements, 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	6,563	7,472
Total liabilities	6,563	7,472
Fair Value, Measurements, 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
Fair Value, Measurements, 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
Fair Value, Measurements, 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
Fair Value, Measurements, 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, Measurements, Recurring | Significant Unobservable Inputs (Level 3) | Long-term investments - other
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value of securities	$ 0	$ 0

Fair Value of Financial Instr38

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, 2018	Mar. 31, 2017
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance	$ 7,472	$ 3,367
Change in fair value of warrant liability included in earnings	(420)	196
Issuance of common stock on warrant exercise	(489)	0
Ending balance	$ 6,563	$ 3,563

Fair Value of Financial Instr39

Fair Value of Financial Instruments - Valuation Assumptions for Warrant Liabilities (Details) - Warrant Liability - Significant Unobservable Inputs (Level 3) - $ / shares	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Common Stock Price (in dollars per share)	$ 16.55	$ 11.40
Risk free interest rate	2.37%	1.70%
Expected life	2 years 7 months 2 days	3 years 11 months 1 day
Expected volatility	30.10%	30.50%
Dividend yield	0.00%	0.00%

Term Loan - Narrative (Details)

Term Loan - Narrative (Details) - USD ($)	Nov. 10, 2015	Mar. 31, 2018	Mar. 31, 2017	Oct. 25, 2017
Debt Instrument [Line Items]
Term loan		$ 146,250,000
Unamortized issue discount and issuance and modification costs		2,400,000
Interest expense		$ 3,419,000	$ 3,494,000
Credit Agreement
Debt Instrument [Line Items]
Debt instrument covenant, maximum debt-to-total capitalization ratio		35.00%
Debt instrument covenant, maximum risk-to-capital ratio		22
Debt instrument, covenant, minimum liquidity requirement		$ 2,300,000
Senior Secured Debt | Credit Agreement
Debt Instrument [Line Items]
Debt instrument, face amount	$ 150,000,000
Debt instrument term	3 years
Periodic payment of principal		375,000
Term loan		$ 146,300,000
Debt issuance costs	$ 4,900,000
Percentage of debt discount	1.00%
Senior Secured Debt | Credit Agreement | Eurodollar
Debt Instrument [Line Items]
Variable rate floor		1.00%
Basis spread on variable rate		6.75%
Interest rate during period		8.54%
Senior Secured Debt | Credit Agreement Amendment
Debt Instrument [Line Items]
Debt issuance costs				$ 445,000

Term Loan - Schedule of Future

Term Loan - Schedule of Future Principal Payments (Details) $ in Thousands	Mar. 31, 2018USD ($)
Future Principal Payments [Abstract]
2,018	$ 1,125
2,019	145,125
Total	$ 146,250

Reinsurance - Narrative (Detail

Reinsurance - Narrative (Details) - USD ($) $ in Thousands	Mar. 31, 2018	May 31, 2017	Mar. 31, 2018	Dec. 31, 2017	Mar. 31, 2017	Dec. 31, 2016
Ceded Credit Risk [Line Items]
Reinsurance recoverable on unpaid claims	$ 2,334		$ 2,334	$ 1,902	$ 564	$ 297
2017 ILN Transaction
Ceded Credit Risk [Line Items]
Optional termination right, percent of reinsurance coverage threshold	10.00%		10.00%
Mortgage-linked Debt | 2017 ILN Notes | Oaktown Re Ltd
Ceded Credit Risk [Line Items]
Proceeds from issuance of notes		$ 211,300
Third-Party Reinsurers | 2017 ILN Transaction
Ceded Credit Risk [Line Items]
Aggregate excess of loss reinsurance coverage	$ 166,600
Aggregate excess of loss reinsurance retained by company		126,800
Risk premiums paid			$ 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 | 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%
Third-Party Reinsurers | Risk Written Policies from January 1, 2018 through December 31, 2019
Ceded Credit Risk [Line Items]
Percent of premiums earned under 2018 QSR Transaction			25.00%
Third-Party Reinsurers | 2016 QSR Transaction
Ceded Credit Risk [Line Items]
Threshold for loss ratio on loans to qualify for profit commission			60.00%
Reinsurance recoverable on unpaid claims	$ 2,300		$ 2,300
Third-Party Reinsurers | Existing Risk Written Policies
Ceded Credit Risk [Line Items]
Percent of premiums ceded under 2016 QSR Transaction			25.00%
Third-Party Reinsurers | Fannie Mae
Ceded Credit Risk [Line Items]
Percent of premiums ceded under 2016 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 2016 QSR Transaction			25.00%

Reinsurance - Effect of Reinsur

Reinsurance - Effect of Reinsurance on Net Premiums Written and Earned (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Net premiums written
Direct	$ 66,027	$ 39,245
Ceded	(6,997)	(4,641)
Net premiums written	59,030	34,604
Net premiums earned
Direct	63,604	37,438
Ceded	(8,690)	(4,213)
Net premiums earned	$ 54,914	$ 33,225

Reinsurance - Amounts Ceded Rel

Reinsurance - Amounts Ceded Related to QSR Transactions (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Ceded Credit Risk [Line Items]
Ceded premiums written (1)	$ (6,997)	$ (4,641)
Ceded premiums earned (1)	(8,690)	(4,213)
Third-Party Reinsurers
Ceded Credit Risk [Line Items]
Ceded risk-in-force	3,304,335	2,167,745
Ceded premiums written (1)	(14,525)	(10,292)
Ceded premiums earned (1)	(16,218)	(9,865)
Ceded claims and claims expenses	543	268
Ceding commission written	2,905	2,058
Ceding commission earned	3,151	2,065
Profit commission	$ 9,201	$ 5,651

Reserves for Insurance Claims45

Reserves for Insurance Claims and Claim Expenses - Narrative (Details) $ in Thousands	3 Months Ended
	Mar. 31, 2018USD ($)loanclaim	Mar. 31, 2017USD ($)	Dec. 31, 2017USD ($)	Dec. 31, 2016USD ($)
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	$ 10,391	$ 3,761	$ 8,761	$ 3,001
Primary loans in default | loan	1,000
Number of claims paid | claim	17
Claims paid, including amounts covered by insurance	$ 482
Favorable prior year development	371	$ 320
Reserve for prior year insurance claims and claim expenses	$ 7,200
Fannie Mae
Liability for Claims and Claims Adjustment Expense [Line Items]
Number of loans in pool past due 60 days or more | loan	64
Risk-in-Force of loans in pool past due 60 days or more	$ 4,200
Loan-to-value ratio (less than)	0.8
Claims applied to pool deductible	$ 492
Deductible on policy	9,900
QSR Transactions
Liability for Claims and Claims Adjustment Expense [Line Items]
Component of claims paid covered under QSR Transaction	$ 111
2016 QSR Transaction
Liability for Claims and Claims Adjustment Expense [Line Items]
Number of covered claims included in number of claims paid | claim	14
2016 QSR Transaction | Fannie Mae
Liability for Claims and Claims Adjustment Expense [Line Items]
Percent of pool RIF reinsured	100.00%

Reserves for Insurance Claims46

Reserves for Insurance Claims and Claim Expenses - Reconciliation of Reserve Balances for Insurance Claims Expense (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Liability for Unpaid Claims and Claims Adjustment Expense [Roll Forward]
Beginning balance	$ 8,761	$ 3,001
Less reinsurance recoverables	1,902	297
Beginning balance, net of reinsurance recoverables	6,859	2,704
Claims incurred:
Current year	1,940	955
Prior years	(371)	(320)
Total claims and claims expenses incurred	1,569	635
Claims and claim expenses paid:
Current year	0	0
Prior years	371	142
Total claims and claim expenses paid	371	142
Ending balance, net of reinsurance recoverables	8,057	3,197
Add reinsurance recoverables	2,334	564
Ending balance	$ 10,391	$ 3,761

Earnings per Share (EPS) - Comp

Earnings per Share (EPS) - Computation of Basic and Diluted Earnings (Loss) per Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended		12 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017
Earnings per Share, Basic [Abstract]
Net income	$ 22,355	$ 5,492	$ 22,050
Basic weighted average shares outstanding (in shares)	62,099	59,184
Basic earnings per share (in dollars per share)	$ 0.36	$ 0.09
Earnings per Share, Diluted [Abstract]
Net income	$ 22,355	$ 5,492	$ 22,050
Warrant gain, net of tax	(332)	0
Diluted net income	$ 22,023	$ 5,492
Basic weighted average shares outstanding (in shares)	62,099	59,184
Dilutive effect of issuable shares	3,598	3,155
Dilutive weighted average shares outstanding (in shares)	65,697	62,339
Diluted earnings per share (in dollars per share)	$ 0.34	$ 0.09
Antidilutive securities excluded from EPS calculation (in shares)	169	1,211

Warrants - Narrative (Details)

Warrants - Narrative (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		12 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017	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
Warrants value				$ 5,100
Warrants exercised (in shares)	54,000	0
Stock issued upon exercise of warrants (in shares)	25,686		32,368
Loss of exercise of warrants	$ 52

Income Taxes - Narrative (Detai

Income Taxes - Narrative (Details) - USD ($) $ in Thousands	3 Months Ended		12 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017	Dec. 31, 2016
Income Tax Disclosure [Abstract]
Effective income tax rate on pre-tax income or loss	15.70%	18.50%
Net operating loss carryforwards			$ 93,300
Provisional income tax expense related to Tax Cuts and Jobs Act of 2017			13,600
Disproportionate tax effects in AOCI	$ 4,200
New Accounting Pronouncements [Line Items]
Cumulative effect of change in accounting principle			0	$ 903
Retained Earnings
New Accounting Pronouncements [Line Items]
Cumulative effect of change in accounting principle			(282)	$ 515
ASU No. 2018-02 | Retained Earnings
New Accounting Pronouncements [Line Items]
Cumulative effect of change in accounting principle			$ (300)

Common Stock Offerings - Narrat

Common Stock Offerings - Narrative (Details) - USD ($) $ in Thousands, shares in Millions	1 Months Ended	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2018	Mar. 31, 2017
Class of Stock [Line Items]
Common stock sold excluding overallotment shares (in shares)	3.7
Common stock offered and sold (in shares)	4.3
Proceeds from issuance of common stock	$ 79,200	$ 79,249	$ 0
Overallotment Option
Class of Stock [Line Items]
Overallotment option included in sale of stock (percent)	15.00%

Regulatory Information - Statut

Regulatory Information - Statutory Net Loss (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Combined
Statutory Accounting Practices [Line Items]
Statutory net loss	$ (6,814)	$ (10,090)

Regulatory Information - Schedu

Regulatory Information - Schedule of Statutory Surplus, Contingency Reserve and Risk-to-Capital Ratio (Details) - Combined $ in Thousands	Mar. 31, 2018USD ($)	Dec. 31, 2017USD ($)
Statutory Accounting Practices [Line Items]
Statutory surplus	$ 368,202	$ 371,084
Contingency reserve	$ 218,518	$ 186,641
Risk-to-Capital	14.4	13.2

Subsequent Event - Narrative (D

Subsequent Event - Narrative (Details) $ in Millions	1 Months Ended
	Apr. 30, 2018USD ($)
Subsequent Event
Subsequent Event [Line Items]
Capital contribution to NMIC	$ 70