Document and Entity Information - shares	3 Months Ended
Document and Entity Information - shares	Mar. 31, 2018	Apr. 27, 2018
Document and Entity Information [Abstract]
Entity Registrant Name	NMI HOLDINGS, INC.
Entity Central Index Key	0001547903
Document Type	10-Q
Document Period End Date	Mar. 31, 2018
Amendment Flag	false
Document Fiscal Year Focus	2018
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 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 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 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 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 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 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

Change in unrealized investment gains/losses, net of tax

2,428

Net income

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

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

^[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

Change in unrealized investment gains/losses, net of tax

(10,956)

Net income

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 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 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 Certain 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 income 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

3 Months Ended

Mar. 31, 2018

Investments, Debt and Equity Securities [Abstract]

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 Cost		Gross Unrealized					Fair Value
	Amortized Cost		Gains		Losses			Fair Value
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 Cost		Gross Unrealized					Fair Value
	Amortized Cost		Gains		Losses			Fair Value
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 Cost		Fair Value
	(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 Cost		Fair Value
	(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 Instruments

3 Months Ended

Mar. 31, 2018

Fair Value Disclosures [Abstract]

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 Active Markets for Identical Assets (Level 1)		Significant Other Observable Inputs (Level 2)		Significant Unobservable Inputs (Level 3)		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 Active Markets for Identical Assets (Level 1)		Significant Other Observable Inputs (Level 2)		Significant Unobservable Inputs (Level 3)		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.

- Definition

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

+ References + Details

Term Loan

3 Months Ended

Mar. 31, 2018

Debt Disclosure [Abstract]

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

3 Months Ended

Mar. 31, 2018

Reinsurance Disclosures [Abstract]

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 and Claim Expenses

3 Months Ended

Mar. 31, 2018

Insurance [Abstract]

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)

3 Months Ended

Mar. 31, 2018

Earnings Per Share [Abstract]

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	3 Months Ended
Warrants	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	3 Months Ended
Income Taxes	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 Certain 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 income 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	3 Months Ended
Common Stock Offerings	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

3 Months Ended

Mar. 31, 2018

Insurance [Abstract]

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	3 Months Ended
Subsequent Event	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 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 Certain 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 income 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.