Debt Disclosure [Abstract] Schedule of Long-term Debt Instruments [Table] Schedule of Long-term Debt Instruments [Table] Long-term Debt, Type [Axis] Long-term Debt, Type [Axis] Long-term Debt, Type [Domain] Long-term Debt, Type [Domain] Senior Secured Debt Senior Secured Debt [Member] Senior Secured Debt [Member] Debt Instrument [Axis] Debt Instrument [Axis] Debt Instrument, Name [Domain] Debt Instrument, Name [Domain] Credit Agreement Credit Agreement [Member] Credit Agreement [Member] Credit Agreement Amendment Credit Agreement Amendment [Member] Credit Agreement Amendment [Member] Variable Rate [Axis] Variable Rate [Axis] Variable Rate [Domain] Variable Rate [Domain] Eurodollar Eurodollar [Member] Debt Instrument [Line Items] Debt Instrument [Line Items] Debt instrument, face amount Debt Instrument, Face Amount Debt instrument term Debt Instrument, Term Variable rate floor Debt Instrument, Variable Interest Rate Floor Debt Instrument, Variable Interest Rate Floor Basis spread on variable rate Debt Instrument, Basis Spread on Variable Rate Interest rate during period Debt Instrument, Interest Rate During Period Periodic payment of principal Debt Instrument, Periodic Payment, Principal Term loan Long-term Debt, Gross Debt issuance costs Debt Issuance Costs, Gross Percentage of debt discount Debt Discount (Premium), Percentage Debt Discount (Premium), Percentage Unamortized issue discount and issuance and modification costs Debt Instrument, Unamortized Discount (Premium) and Debt Issuance Costs, Net Interest expense Interest Expense Debt instrument covenant, maximum debt-to-total capitalization ratio Debt Instrument, Covenant, Debt to Total Capitalization Ratio, Maximum Debt Instrument, Covenant, Debt to Total Capitalization Ratio, Maximum Debt instrument covenant, maximum risk-to-capital ratio Debt Instrument, Covenant, Risk to Capital Ratio, Maximum Debt Instrument, Covenant, Risk to Capital Ratio, Maximum Debt instrument, covenant, minimum liquidity requirement Debt Instrument, Covenant, Liquidity Requirement, Minimum Debt Instrument, Covenant, Liquidity Requirement, Minimum Investments, Debt and Equity Securities [Abstract] Amortized Cost Available-for-sale Securities, Debt Maturities, Single Maturity Date, Amortized Cost Basis [Abstract] Due in one year or less Available-for-sale Securities, Debt Maturities, Next Twelve Months, Amortized Cost Basis Due after one through five years Available-for-sale Securities, Debt Maturities, Year Two Through Five, Amortized Cost Basis Due after five through ten years Available-for-sale Securities, Debt Maturities, Year Six Through Ten, Amortized Cost Basis Due after ten years Available-for-sale Securities, Debt Maturities, after Ten Years, Amortized Cost Basis Asset-backed securities Available-for-sale Securities, Debt Maturities, without Single Maturity Date, Amortized Cost Basis Amortized Cost Available-for-sale Securities, Amortized Cost Basis Fair Value Available-for-sale Securities, Debt Maturities, Single Maturity Date [Abstract] Due in one year or less Available-for-sale Securities, Debt Maturities, Next Twelve Months, Fair Value Due after one through five years Available-for-sale Securities, Debt Maturities, Year Two Through Five, Fair Value Due after five through ten years Available-for-sale Securities, Debt Maturities, Year Six Through Ten, Fair Value Due after ten years Available-for-sale Securities, Debt Maturities, after Ten Years, Fair Value Asset-backed securities Available-for-sale Securities, Debt Maturities, without Single Maturity Date, Fair Value Fair Value Available-for-sale Securities Schedule of Available-for-sale Securities [Table] Schedule of Available-for-sale Securities [Table] Major Types of Debt and Equity Securities [Axis] Major Types of Debt and Equity Securities [Axis] Major Types of Debt and Equity Securities [Domain] Major Types of Debt and Equity Securities [Domain] U.S. Treasury securities and obligations of U.S. government agencies US Treasury and Government [Member] Municipal debt securities US States and Political Subdivisions Debt Securities [Member] Corporate debt securities Corporate Debt Securities [Member] Asset-backed securities Asset-backed Securities [Member] Bonds Bonds [Member] Long-term investments - other Other Debt Obligations [Member] Short-term investments Short-term Investments [Member] Schedule of Available-for-sale Securities [Line Items] Schedule of Available-for-sale Securities [Line Items] Gross Unrealized Gains Available-for-sale Securities, Accumulated Gross Unrealized Gain, before Tax Gross Unrealized (Losses) Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax Fair Value Income Tax Disclosure [Abstract] Effective income tax rate on pre-tax income or loss Effective Income Tax Rate Reconciliation, Percent Net operating loss carryforwards Operating Loss Carryforwards Provisional income tax expense related to Tax Cuts and Jobs Act of 2017 Tax Cuts and Jobs Act of 2017, Incomplete Accounting, Change in Tax Rate, Provisional Income Tax Expense (Benefit) Tax Cuts and Jobs Act of 2017, Incomplete Accounting, Change in Tax Rate, Provisional Income Tax Expense (Benefit) Disproportionate tax effects in AOCI AOCI Tax, Attributable to Parent New Accounting Pronouncements or Change in Accounting Principle [Table] New Accounting Pronouncements or Change in Accounting Principle [Table] Adjustments for New Accounting Pronouncements [Axis] Adjustments for New Accounting Pronouncements [Axis] Type of Adoption [Domain] Type of Adoption [Domain] ASU No. 2018-02 Accounting Standards Update 2018-02 [Member] Accounting Standards Update 2018-02 [Member] Equity Components [Axis] Equity Components [Axis] Equity Component [Domain] Equity Component [Domain] Retained Earnings Retained Earnings [Member] New Accounting Pronouncements [Line Items] New Accounting Pronouncements or Change in Accounting Principle [Line Items] Cumulative effect of change in accounting principle Cumulative Effect of New Accounting Principle in Period of Adoption Insurance [Abstract] Statutory Accounting Practices [Table] Statutory Accounting Practices [Table] Legal Entity [Axis] Legal Entity [Axis] Entity [Domain] Entity [Domain] Combined NMic and Re one Combined [Member] NMic and Re one Combined [Member] Statutory Accounting Practices [Line Items] Statutory Accounting Practices [Line Items] Statutory surplus Statutory Accounting Practices, Statutory Capital and Surplus, Balance Contingency reserve Statutory Accounting Practices, Contingency Reserve Contingency reserve recorded under Statutory Accounting Principles is a liability to protect against loss during periods of extreme contraction. Risk-to-Capital Risk To Capital Ratio Regulatory Actual This concept represents an entity's ratio of net risk in force (excludes risk ceded through reinsurance contracts and risk in force on defaulted loans) to the amount of statutory capital (defined as the sum of statutory policyholders' surplus plus statutory contingency reserves). Fair Value Disclosures [Abstract] Fair Value Measurements, Recurring and Nonrecurring [Table] Fair Value Measurements, Recurring and Nonrecurring [Table] Measurement Frequency [Axis] Measurement Frequency [Axis] Fair Value, Measurement Frequency [Domain] Fair Value, Measurement Frequency [Domain] Fair Value, Measurements, Recurring Fair Value, Measurements, Recurring [Member] Fair Value, Hierarchy [Axis] Fair Value, Hierarchy [Axis] Fair Value Hierarchy [Domain] Fair Value Hierarchy [Domain] Quoted Prices in Active Markets for Identical Assets (Level 1) Fair Value, Inputs, Level 1 [Member] Significant Other Observable Inputs (Level 2) Fair Value, Inputs, Level 2 [Member] Significant Unobservable Inputs (Level 3) Fair Value, Inputs, Level 3 [Member] Municipal debt securities Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] Fair value of securities Cash, cash equivalents and short-term investments Cash and Cash Equivalents, Fair Value Disclosure Total assets Assets, Fair Value Disclosure Warrant liability Warrant Liability Warrant Liability Total liabilities Financial and Nonfinancial Liabilities, Fair Value Disclosure Statement of Stockholders' Equity [Abstract] Statement [Table] Statement [Table] Common Stock - Class A Common Stock [Member] Additional Paid-in Capital Additional Paid-in Capital [Member] Accumulated Other Comprehensive Income (Loss) AOCI Attributable to Parent [Member] Accumulated Deficit Statement [Line Items] Statement [Line Items] Increase (Decrease) in Stockholders' Equity [Roll Forward] Increase (Decrease) in Stockholders' Equity [Roll Forward] Beginning balance Stockholders' Equity Attributable to Parent Beginning balance (in shares) Shares, Outstanding Common stock: class A shares issued related to public offering Stock Issued During Period, Value, New Issues Common stock: class A shares issued related to public offering (in shares) Stock Issued During Period, Shares, New Issues Common stock: class A shares issued related to warrants Stock Issued During Period, Value, Conversion of Convertible Securities Common stock: class A shares issued related to warrants (in shares) Stock Issued During Period, Shares, Conversion of Convertible Securities Common stock: class A shares issued under stock plans, net of shares withheld for employee taxes Stock Issued During Period, Value, Employee Stock Purchase Plan, Net of Tax Withholdings Stock Issued During Period, Value, Employee Stock Purchase Plan, Net of Tax Withholdings Common stock: class A shares issued under stock plans, net of shares withheld for employee taxes (in shares) Stock Issued During Period, Shares, Employee Stock Purchase Plans, Net of Shares For Tax Withholdings Stock Issued During Period, Shares, Employee Stock Purchase Plans, Net of Shares For Tax Withholdings Share-based compensation expense Adjustments to Additional Paid in Capital, Share-based Compensation, Requisite Service Period Recognition Change in unrealized investment gains/losses, net of tax Other Comprehensive Income (Loss), Available-for-sale Securities Adjustment, Net of Tax Net income Net Income (Loss) Attributable to Parent Ending balance Ending balance (in shares) Future Principal Payments [Abstract] Long-term Debt, Fiscal Year Maturity [Abstract] 2018 Long-term Debt, Maturities, Repayments of Principal, Remainder of Fiscal Year 2019 Long-term Debt, Maturities, Repayments of Principal in Year Two Total Reinsurance Disclosures [Abstract] Net premiums written Premiums Written, Net [Abstract] Direct Direct Premiums Written Ceded Ceded Premiums Written Net premiums written Premiums Written, Net Net premiums earned Premiums Earned, Net [Abstract] Direct Direct Premiums Earned Ceded Ceded Premiums Earned Net premiums earned Premiums Earned, Net Earnings Per Share [Abstract] Schedule of Earnings per Share, Basic and Diluted Schedule of Earnings Per Share, Basic and Diluted [Table Text Block] Warrants issued (in shares) Class of Warrant or Right, Number of Securities Called by Warrants or Rights Right to purchase, number of shares per warrant Number Of Shares, Right To Purchase Per Warrant Number Of Shares, Right To Purchase Per Warrant Exercise price of warrants (in dollars per warrant) Class of Warrant or Right, Exercise Price of Warrants or Rights Warrants value Warrants and Rights Outstanding Warrants exercised (in shares) Class of Warrant or Right, Number of Warrants Exercised During Period Class of Warrant or Right, Number of Warrants Exercised During Period Stock issued upon exercise of warrants (in shares) Loss of exercise of warrants Class of Warrant or Right, Exercise Of Warrants, Gain (Loss) Class of Warrant or Right, Exercise Of Warrants, Gain (Loss) Term Loan Debt Disclosure [Text Block] Statement of Cash Flows [Abstract] Cash flows from operating activities Net Cash Provided by (Used in) Operating Activities [Abstract] Net income Adjustments to reconcile net income to net cash provided by (used in) operating activities: Adjustments to Reconcile Net Income (Loss) to Cash Provided by (Used in) Operating Activities [Abstract] Net realized investment losses Available-for-sale Securities, Gross Realized Gain (Loss) (Gain) Loss from change in fair value of warrant liability Fair Value Adjustment of Warrants Depreciation and amortization Depreciation, Amortization and Accretion, Net Net amortization of premium on investment securities Accretion (Amortization) of Discounts and Premiums, Investments Amortization of debt discount and debt issuance costs Amortization of Debt Issuance Costs and Discounts Share-based compensation expense Share-based Compensation Deferred income taxes Deferred Income Taxes and Tax Credits Changes in operating assets and liabilities: Increase (Decrease) in Other Operating Assets and Liabilities, Net [Abstract] Premiums receivable Increase (Decrease) in Premiums Receivable Accrued investment income Increase (Decrease) in Accrued Investment Income Receivable Prepaid expenses Increase (Decrease) in Prepaid Expense Deferred policy acquisition costs, net Increase (Decrease) in Deferred Policy Acquisition Costs Other assets Increase (Decrease) in Prepaid Expense and Other Assets Unearned premiums Increase (Decrease) in Unearned Premiums Reserve for insurance claims and claim expenses Increase (Decrease) in Liability for Claims and Claims Adjustment Expense Reserve Reinsurance balances, net Increase (Decrease) in Reinsurance Assets and Liabilities Increase (Decrease) in Reinsurance Assets and Liabilities Accounts payable and accrued expenses Increase (Decrease) in Accounts Payable and Accrued Liabilities Net cash provided by (used in) operating activities Net Cash Provided by (Used in) Operating Activities Cash flows from investing activities Net Cash Provided by (Used in) Investing Activities [Abstract] Purchase of short-term investments Payments to Acquire Short-term Investments Purchase of fixed-maturity investments, available-for-sale Payments to Acquire Available-for-sale Securities, Debt Proceeds from maturity of short-term investments Proceeds from Sale of Short-term Investments Proceeds from redemptions, maturities and sale of fixed-maturity investments, available-for-sale Proceeds from Sale and Maturity of Available-for-sale Securities Additions to software and equipment Payments to Acquire Property, Plant, and Equipment Net cash used in investing activities Net Cash Provided by (Used in) Investing Activities Cash flows from financing activities Net Cash Provided by (Used in) Financing Activities [Abstract] Proceeds from issuance of common stock related to public offering Proceeds from Issuance of Common Stock Proceeds from issuance of common stock related to employee equity plans Proceeds from Issuance of Shares under Incentive and Share-based Compensation Plans, Including Stock Options Taxes paid related to net share settlement of equity awards Payments Related to Tax Withholding for Share-based Compensation Repayments of term loan Repayments of Long-term Debt Payments of debt modification costs Payments of Debt Issuance Costs Net cash provided by (used in) financing activities Net Cash Provided by (Used in) Financing Activities Net increase (decrease) in cash and cash equivalents Cash and Cash Equivalents, Period Increase (Decrease) Cash and cash equivalents, beginning of period Cash and Cash Equivalents, at Carrying Value Cash and cash equivalents, end of period Supplemental disclosures of cash flow information Supplemental Cash Flow Information [Abstract] Interest paid Interest Paid Income taxes paid Income Taxes Paid Organization, Consolidation and Presentation of Financial Statements [Abstract] Schedule of Business Acquisitions, by Acquisition [Table] Schedule of Business Acquisitions, by Acquisition [Table] Class of Stock [Axis] Class of Stock [Axis] Class of Stock [Domain] Class of Stock [Domain] Common Stock - Class A Common Class A [Member] Business Acquisition [Axis] Business Acquisition [Axis] Business Acquisition, Acquiree [Domain] Business Acquisition, Acquiree [Domain] MAC Financial Holding Corporation and Subsidiaries MAC Financial Holding Corporation and Subsidiaries [Member] MAC Financial Holding Corporation and Subsidiaries [Member] Sale of Stock [Axis] Sale of Stock [Axis] Sale of Stock [Domain] Sale of Stock [Domain] Private Placement Private Placement [Member] IPO IPO [Member] Overallotment Option Over-Allotment Option [Member] Business Acquisition [Line Items] Business Acquisition [Line Items] Common stock offered and sold (in shares) Proceeds from issuance of common stock, net of stock issuance costs Proceeds From Issuance of Common Stock, Net of Stock Issuance Costs Proceeds From Issuance of Common Stock, Net of Stock Issuance Costs Cash, common stock and warrants issued for acquisition Business Combination, Consideration Transferred, Cash and Equity Interests Issued and Issuable Business Combination, Consideration Transferred, Cash and Equity Interests Issued and Issuable Liabilities assumed in acquisition Business Combination, Consideration Transferred, Liabilities Incurred Overallotment option included in sale of stock (percent) Stock Issued During Period, Overallotment Option, Percent Stock Issued During Period, Overallotment Option, Percent Number of states in which the entity operates Number of States in which Entity Operates Basis of Presentation Basis of Accounting, Policy [Policy Text Block] Reinsurance Reinsurance Accounting Policy [Policy Text Block] Recent Accounting Pronouncements New Accounting Pronouncements, Policy [Policy Text Block] Earnings Per Share Earnings Per Share, Policy [Policy Text Block] Liability for Claims and Claims Adjustment Expense [Table] Liability for Claims and Claims Adjustment Expense [Table] Reinsurance Policy, Type [Axis] Reinsurance Policy, Type [Axis] Reinsurance Policy [Domain] Reinsurance Policy [Domain] QSR Transactions QSR Transactions [Member] QSR Transactions [Member] 2016 QSR Transaction Two Thousand Sixteen QSR Transaction [Member] Two Thousand Sixteen QSR Transaction [Member] Counterparty Name [Axis] Counterparty Name [Axis] Counterparty Name [Domain] Counterparty Name [Domain] Fannie Mae Fannie Mae [Member] Fannie Mae [Member] Liability for Claims and Claims Adjustment Expense [Line Items] Liability for Claims and Claims Adjustment Expense [Line Items] IBNR, default period (at least) Liability for Unpaid Claims and Claims Adjustment Expense, Incurred but Not Reported (IBNR) Claims, Default Period Liability for Unpaid Claims and Claims Adjustment Expense, Incurred but Not Reported (IBNR) Claims, Default Period Total gross liability for unpaid claims and claim adjustment expenses Liability for Claims and Claims Adjustment Expense Primary loans in default Liability for Unpaid Claims and Claims Adjustment Expense, Incurred but Not Reported (IBNR) Claims, Number of Primary Loans in Default Liability for Unpaid Claims and Claims Adjustment Expense, Incurred but Not Reported (IBNR) Claims, Number of Primary Loans in Default Number of claims paid Liability for Paid Claims and Claims Adjustment Expense, Number of Paid Claims Liability for Paid Claims and Claims Adjustment Expense, Number of Paid Claims Claims paid, including amounts covered by insurance Liability for Unpaid Claims and Claims Adjustment Expense, Claims Paid Including Amounts Covered By Insurance Amount of payments to settle insured claims and pay costs incurred in the claims settlement process, including amount covered by insurance. Number of covered claims included in number of claims paid Liability for Paid Claims and Claims Adjustment Expense, Number of Covered Claims Included In Number of Paid Claims Liability for Paid Claims and Claims Adjustment Expense, Number of Covered Claims Included In Number of Paid Claims Component of claims paid covered under QSR Transaction Liability for Unpaid Claims and Claims Adjustment Expense, Claims Paid Including Amounts Covered By Insurance, Amount Under QSR Transaction Component of total amount of payments to settle insured claims and pay costs incurred in the claims settlement process, including amount covered by insurance, covered under QSR transaction. Number of loans in pool past due 60 days or more Loans In Pool, Past Due 60 Days Or More, Number Of Loans Loans In Pool, Past Due 60 Days Or More, Number Of Loans Risk-in-Force of loans in pool past due 60 days or more Loans In Pool, Past Due 60 Days Or More, Loan Risk in Force Loans In Pool, Past Due 60 Days Or More, Risk in Force Loan-to-value ratio (less than) Loans In Pool, Loan To Value Ratio Loans In Pool, Loan To Value Ratio Claims applied to pool deductible Liability for Unpaid Claims and Claims Adjustment Expense, Claims Applied to Deductible Liability for Unpaid Claims and Claims Adjustment Expense, Claims Applied to Deductible Deductible on policy Mortgage Pool Insurance, Claim Deductible Mortgage Pool Insurance, Claim Deductible Percent of pool RIF reinsured Reinsurance Retention Policy, Reinsured Risk, Percentage Favorable prior year development Prior Year Claims and Claims Adjustment Expense Reserve for prior year insurance claims and claim expenses Liability for Prior Year Claims and Claims Adjustment Expense Liability for Prior Year Claims and Claims Adjustment Expense Subsequent Events [Abstract] Subsequent Event Subsequent Events [Text Block] Cash and investments held with various state insurance departments Cash, Cash Equivalents, and Short-term Investments Unrealized loss position, accumulated loss Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss Unrealized loss position, 12 months or greater Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss Other-than-temporary impairment Other than Temporary Impairment Losses, Investments, Portion Recognized in Earnings, Net, Available-for-sale Securities Statutory net loss Statutory Accounting Practices, Statutory Net Income Amount Earnings per Share (EPS) Earnings Per Share [Text Block] Ceded Credit Risk [Table] Ceded Credit Risk [Table] Ceded Credit Risk, Reinsurer [Axis] Ceded Credit Risk, Reinsurer [Axis] Ceded Credit Risk, Reinsurer [Domain] Ceded Credit Risk, Reinsurer [Domain] Third-Party Reinsurers Third-Party Reinsurers [Member] Third-Party Reinsurers [Member] Mortgage-linked Debt Secured Debt [Member] 2017 ILN Notes Two Thousand Seventeen ILN Notes [Member] Two Thousand Seventeen ILN Notes [Member] Oaktown Re Ltd Oaktown Re Ltd [Member] Oaktown Re Ltd [Member] 2017 ILN Transaction Two Thousand Seventeen ILN Transaction [Member] Two Thousand Seventeen ILN Transaction [Member] 2018 QSR Transaction Two Thousand Eighteen QSR Transaction [Member] Two Thousand Eighteen QSR Transaction [Member] Risk Written Policies from January 1, 2018 through December 31, 2019 Eligible Policies, Pool Four [Member] Eligible Policies, Pool Four [Member] Existing Risk Written Policies Eligible Policies, Pool One [Member] Eligible Policies, Pool One [Member] Fannie Mae Eligible Policies, Pool Two [Member] Eligible Policies, Pool Two [Member] Risk Written Policies from September 1, 2016 through December 31, 2017 Eligible Policies, Pool Three [Member] Eligible Policies, Pool Three [Member] Range [Axis] Range [Axis] Range [Domain] Range [Domain] Maximum Maximum [Member] Ceded Credit Risk [Line Items] Ceded Credit Risk [Line Items] Aggregate excess of loss reinsurance coverage Reinsurance Retention Policy, Excess Retention, Amount Reinsured Aggregate excess of loss reinsurance retained by company Reinsurance Retention Policy, Amount Retained Reinsurance coverage, term of underlying mortgage amortization (in years) Reinsurance Retention Policy, Term Of Underlying Mortgage Amortization Reinsurance Retention Policy, Term Of Underlying Mortgage Amortization Proceeds from issuance of notes Proceeds from Issuance of Debt Anticipated payment related to annual operating expenses Anticipated Operating Expense Payments, Annual Amount of anticipated payments related to operating expenses of counterparty. Risk premiums paid Reinsurance Retention, Risk Premiums Paid Reinsurance Retention, Risk Premiums Paid Optional termination right, percent of reinsurance coverage threshold Reinsurance Agreement, Optional Termination Right, Percent Of Reinsurance Coverage Threshold Reinsurance Agreement, Optional Termination Right, Percent Of Reinsurance Coverage Threshold Percent of premiums earned under 2018 QSR Transaction Premiums Earned, Percent Of Risk Premiums Earned, Percent Of Risk Percent of premiums ceded under 2016 QSR Transaction Ceding commissions under 2016 QSR Transaction Ceded Credit Risk, Commission Earned, Percentage Ceded Credit Risk, Commission Earned, Percentage Threshold for loss ratio on loans to qualify for profit commission Ceded Credit Risk, Profit Commission, Loss Ratio On Loans Threshold Ceded Credit Risk, Profit Commission, Loss Ratio On Loans Threshold Reinsurance recoverable on unpaid claims Reinsurance Recoverable for Paid and Unpaid Claims and Claims Adjustments Statement of Financial Position [Abstract] Assets Assets [Abstract] 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) Available-for-sale Securities, Debt Securities Cash and cash equivalents Premiums receivable Premiums Receivable, Net Accrued investment income Accrued Investment Income Receivable Prepaid expenses Prepaid Expense Deferred policy acquisition costs, net Deferred Policy Acquisition Costs Software and equipment, net Property, Plant and Equipment, Net Intangible assets and goodwill Intangible Assets, Net (Including Goodwill) Prepaid reinsurance premiums Prepaid Reinsurance Premiums Deferred tax asset, net Deferred Income Tax Assets, Net Other assets Other Assets Total assets Assets Liabilities Liabilities [Abstract] Term loan Long-term Debt Unearned premiums Unearned Premiums Accounts payable and accrued expenses Accounts Payable and Accrued Liabilities Reserve for insurance claims and claim expenses Reinsurance funds withheld Funds Held under Reinsurance Agreements, Liability Deferred ceding commission Deferred Revenue Warrant liability, at fair value Total liabilities Liabilities Commitments and contingencies Commitments and Contingencies Shareholders' Equity Stockholders' Equity Attributable to Parent [Abstract] 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) Common Stock, Value, Outstanding Additional paid-in capital Additional Paid in Capital Accumulated other comprehensive loss, net of tax Accumulated Other Comprehensive Income (Loss), Net of Tax Accumulated deficit Retained Earnings (Accumulated Deficit) Total shareholders' equity Total liabilities and shareholders' equity Liabilities and Equity Schedule of Effects of Reinsurance Effects of Reinsurance [Table Text Block] Income Statement [Abstract] Revenues Revenues [Abstract] Net premiums earned Net investment income Net Investment Income Net realized investment losses Other revenues Other Revenue, Net Total revenues Revenues Expenses Costs and Expenses [Abstract] Insurance claims and claim expenses Policyholder Benefits and Claims Incurred, Net, Property, Casualty and Liability Underwriting and operating expenses Other Cost and Expense, Operating Total expenses Costs and Expenses Other expense Other Income and Expenses [Abstract] Gain (Loss) from change in fair value of warrant liability Gain (Loss) on Change in Fair Value of Warrant Liability Gain (Loss) on Change in Fair Value of Warrant Liability Interest expense Total other expense Other Nonoperating Income (Expense) Income before income taxes Income (Loss) from Continuing Operations before Income Taxes, Noncontrolling Interest Income tax expense Income Tax Expense (Benefit) Net income Earnings per share Earnings Per Share, Basic and Diluted [Abstract] Basic earnings per share (in dollars per share) Earnings Per Share, Basic Diluted earnings per share (in dollars per share) Earnings Per Share, Diluted Weighted average common shares outstanding Weighted Average Number of Shares Outstanding Reconciliation [Abstract] Basic weighted average shares outstanding (in shares) Weighted Average Number of Shares Outstanding, Basic Dilutive weighted average shares outstanding (in shares) Weighted Average Number of Shares Outstanding, Diluted Other comprehensive income (loss), net of tax: Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Parent [Abstract] 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 Other Comprehensive Income (Loss), Unrealized Holding Gain (Loss) on Securities Arising During Period, Net of Tax 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 Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI for Sale of Securities, Net of Tax Other comprehensive income (loss), net of tax Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Parent Comprehensive income Comprehensive Income (Loss), Net of Tax, Attributable to Parent Number of securities, less than 12 months Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions, Less than One Year Fair value, less than 12 months Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value Unrealized losses, less than 12 months Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss Number of securities,12 months or greater Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions, Greater than or Equal to One Year Fair value, 12 months or greater Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value Unrealized losses, 12 months or greater Number of securities, total Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions Fair value Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value Unrealized Losses Equity [Abstract] Schedule of Stock by Class [Table] Schedule of Stock by Class [Table] Class of Stock [Line Items] Class of Stock [Line Items] Common stock sold excluding overallotment shares (in shares) Stock Issued During Period, Shares, New Issues Before Overallotment Stock Issued During Period, Shares, New Issues Before Overallotment Proceeds from issuance of common stock Subsequent Event [Table] Subsequent Event [Table] Subsequent Event Type [Axis] Subsequent Event Type [Axis] Subsequent Event Type [Domain] Subsequent Event Type [Domain] Subsequent Event Subsequent Event [Member] Subsequent Event [Line Items] Subsequent Event [Line Items] Capital contribution to NMIC Payments to Acquire Interest in Subsidiaries and Affiliates Organization, Basis of Presentation and Summary of Accounting Principles Business Description and Basis of Presentation [Text Block] Schedule of Statutory Net Loss, Surplus, Contingency Reserve and Risk-to-Capital Ratio Statutory Accounting Practices Disclosure [Table Text Block] Income Taxes Income Tax Disclosure [Text Block] Investments Investments in Debt and Marketable Equity Securities (and Certain Trading Assets) Disclosure [Text Block] Warrants Line of Credit and Related Warrants [Text Block] Line of Credit and Related Warrants [Text Block] Liability Class [Axis] Liability Class [Axis] Fair Value by Liability Class [Domain] Fair Value by Liability Class [Domain] Warrant Liability Warrant Liability [Member] Warrant Liability [Member] Common Stock Price (in dollars per share) Share Price Risk free interest rate Fair Value Assumptions, Risk Free Interest Rate Expected life Fair Value Assumptions, Expected Term Expected volatility Fair Value Assumptions, Expected Volatility Rate Dividend yield Fair Value Assumptions, Expected Dividend Rate Liability for Unpaid Claims and Claims Adjustment Expense [Roll Forward] Liability for Unpaid Claims and Claims Adjustment Expense [Roll Forward] Beginning balance Less reinsurance recoverables Beginning balance, net of reinsurance recoverables Liability for Unpaid Claims and Claims Adjustment Expense, Net Claims incurred: Liability for Unpaid Claims and Claims Adjustment Expense, Incurred Claims [Abstract] Current year Current Year Claims and Claims Adjustment Expense Prior years Total claims and claims expenses incurred Liability for Unpaid Claims and Claims Adjustment Expense, Incurred Claims Claims and claim expenses paid: Liability for Unpaid Claims and Claims Adjustment Expense, Claims Paid [Abstract] Current year Liability for Unpaid Claims and Claims Adjustment Expense, Claims Paid, Current Year Prior years Liability for Unpaid Claims and Claims Adjustment Expense, Claims Paid, Prior Years Total claims and claim expenses paid Liability for Unpaid Claims and Claims Adjustment Expense, Claims Paid Ending balance, net of reinsurance recoverables Add reinsurance recoverables Ending balance Regulatory Information Insurance Disclosure [Text Block] Change in unrealized investment gains/losses, tax (benefit) expense Other Comprehensive Income (Loss), Available-for-sale Securities, Tax Common stock, par value (in dollars per share) Common Stock, Par or Stated Value Per Share Fixed maturities, available-for-sale, amortized cost Available-for-sale Debt Securities, Amortized Cost Basis Common stock, issued (in shares) Common Stock, Shares, Issued Common stock, outstanding (in shares) Common Stock, Shares, Outstanding Common stock, authorized (in shares) Common Stock, Shares Authorized Earnings per Share, Basic [Abstract] Net Income (Loss) Available to Common Stockholders, Operations, Basic [Abstract] Earnings per Share, Diluted [Abstract] Net Income (Loss) Available to Common Stockholders, Operations, Diluted [Abstract] Warrant gain, net of tax Amount Of Dilutive Securities Warrants Amount of increase (decrease) to net income used for calculating diluted earnings per share (EPS), resulting from warrant losses (gains). Diluted net income Net Income (Loss) Attributable to Parent, Diluted Dilutive effect of issuable shares Weighted Average Number Diluted Shares Outstanding Adjustment Dilutive weighted average shares outstanding (in shares) Antidilutive securities excluded from EPS calculation (in shares) Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount Ceded risk-in-force Risk In Force, Ceded Risk In Force, Ceded Ceded premiums written (1) Ceded premiums earned (1) Ceded claims and claims expenses Reinsurance Ceded Claims and Claims Expenses Reinsurance Ceded Claims and Claims Expenses Ceding commission written Reinsurance Ceding Commission Written Reinsurance Ceding Commission Written Ceding commission earned Reinsurance Ceding Commission Earned Reinsurance Ceding Commission Earned Profit commission Reinsurance Profit Commission Reinsurance Profit Commission Investment Income, Net [Abstract] Investment Income, Net [Abstract] Investment income Investment Income, Interest and Dividend Investment expenses Investment Income, Investment Expense Net investment income Investment Income, Net Net unrealized (losses) gains in accumulated other comprehensive income, tax (benefit) expense Other Comprehensive Income (Loss), Unrealized Holding Gain (Loss) on Securities Arising During Period, Tax Reclassification adjustment for realized losses included in net income, tax expense Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI for Sale of Securities, Tax Schedule of Future Principal Payments Schedule of Maturities of Long-term Debt [Table Text Block] Document and Entity Information [Abstract] Document and Entity Information [Abstract] Entity Registrant Name Entity Registrant Name Entity Central Index Key Entity Central Index Key Document Type Document Type Document Period End Date Document Period End Date Amendment Flag Amendment Flag Document Fiscal Year Focus Document Fiscal Year Focus Document Fiscal Period Focus Document Fiscal Period Focus Current Fiscal Year End Date Current Fiscal Year End Date Entity Filer Category Entity Filer Category Entity Common Stock, Shares Outstanding Entity Common Stock, Shares Outstanding Reinsurance Reinsurance [Text Block] Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Table] Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Table] Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items] Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items] Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward] Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward] Beginning balance Fair Value, Measurement with Unobservable Inputs Reconciliations, Recurring Basis, Liability Value Change in fair value of warrant liability included in earnings Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Liability, Gain (Loss) Included in Earnings Issuance of common stock on warrant exercise Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Liability, Settlements Ending balance Gross realized investment gains Available-for-sale Securities, Gross Realized Gains Gross realized investment losses Available-for-sale Securities, Realized Losses, Excluding Other than Temporary Impairments Net realized investment gains (losses) Available-for-sale Securities, Gross Realized Gain (Loss), Excluding Other than Temporary Impairments Fair Value of Financial Instruments Fair Value Disclosures [Text Block] Schedule of Fair Value Measurements of Financial Instruments Fair Value Measurements, Recurring and Nonrecurring [Table Text Block] Roll-Forward of Level 3 Liabilities Measured at Fair Value Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Table Text Block] Schedule of Key Inputs and Assumptions in Option-Pricing Model Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Table Text Block] Schedule of Fair Values and Gross Unrealized Gains and Losses Available-for-sale Securities [Table Text Block] Schedule of Investments by Maturity Investments Classified by Contractual Maturity Date [Table Text Block] Schedule of Aging Unrealized Losses Schedule of Unrealized Loss on Investments [Table Text Block] Schedule of Net Investment Income Investment Income [Table Text Block] Schedule of Net Realized Investment Gains (Losses) Realized Gain (Loss) on Investments [Table Text Block] Reconciliation of Liability for Insurance Claims and Claims Expenses Schedule of Liability for Unpaid Claims and Claims Adjustment Expense [Table Text Block] Common Stock Offerings Stockholders' Equity Note Disclosure [Text Block] Reserves for Insurance Claims and Claim Expenses Liability for Future Policy Benefits and Unpaid Claims Disclosure [Text Block]