Statement of Stockholders' Equity [Abstract] Statement [Table] Statement [Table] Equity Components [Axis] Equity Components [Axis] Equity Component [Domain] Equity Component [Domain] 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] Retained Earnings Retained Earnings [Member] 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 Cumulative effect of change in accounting principle Cumulative Effect of New Accounting Principle in Period of Adoption 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 APIC, Share-based Payment Arrangement, Increase for Cost Recognition Change in unrealized investment gains/losses, net of tax Other Comprehensive Income (Loss), Securities, Available-for-sale, Adjustment, after Tax Net income Net Income (Loss) Attributable to Parent Ending balance Ending balance (in shares) Statement of Financial Position [Abstract] Assets Assets [Abstract] Fixed maturities, available-for-sale, at fair value (amortized cost of $994,543 and $924,987 as of June 30, 2019 and December 31, 2018, respectively) Debt Securities, Available-for-sale Cash and cash equivalents (including restricted cash of $1,430 and $1,414 as of June 30, 2019 and December 31, 2018, respectively) Cash, Cash Equivalents, Restricted Cash and Restricted 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 Cost Software and equipment, net Property, Plant and Equipment, Net Intangible assets and goodwill Intangible Assets, Net (Including Goodwill) Prepaid reinsurance premiums Prepaid Reinsurance Premiums 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 Liability for Claims and Claims Adjustment Expense Reinsurance funds withheld Funds Held under Reinsurance Agreements, Liability Warrant liability, at fair value Warrants and Rights Outstanding Deferred tax liability, net Deferred Income Tax Liabilities, Net Other liabilities Other Liabilities 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; 67,768,466 and 66,318,849 shares issued and outstanding as of June 30, 2019 and December 31, 2018, respectively (250,000,000 shares authorized) Common Stock, Value, Outstanding Additional paid-in capital Additional Paid in Capital Accumulated other comprehensive income (loss), net of tax Accumulated Other Comprehensive Income (Loss), Net of Tax Retained earnings Retained Earnings (Accumulated Deficit) Total shareholders' equity Total liabilities and shareholders' equity Liabilities and Equity Leases [Abstract] Future Minimum Lease Payments as Accounted for Prior to Adoption of ASU 2016-02 Operating Leases, Future Minimum Payments Due, Fiscal Year Maturity [Abstract] 2019 Operating Leases, Future Minimum Payments Due, Next Twelve Months 2020 Operating Leases, Future Minimum Payments, Due in Two Years 2021 Operating Leases, Future Minimum Payments, Due in Three Years 2022 Operating Leases, Future Minimum Payments, Due in Four Years 2023 Operating Leases, Future Minimum Payments, Due in Five Years Totals Operating Leases, Future Minimum Payments Due Earnings Per Share [Abstract] Earnings per Share, Basic [Abstract] Net Income (Loss) Available to Common Stockholders, Operations, Basic [Abstract] Net income Basic weighted average shares outstanding (in shares) Weighted Average Number of Shares Outstanding, Basic Basic earnings per share (in dollars per share) Earnings Per Share, Basic 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 (in shares) Weighted Average Number Diluted Shares Outstanding Adjustment Dilutive weighted average shares outstanding (in shares) Weighted Average Number of Shares Outstanding, Diluted Diluted earnings per share (in dollars per share) Earnings Per Share, Diluted Antidilutive securities excluded from EPS calculation (in shares) Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount Debt Disclosure [Abstract] Future Principal Payments [Abstract] Long-term Debt, Fiscal Year Maturity [Abstract] 2019 Long-term Debt, Maturities, Repayments of Principal, Remainder of Fiscal Year 2020 Long-term Debt, Maturities, Repayments of Principal in Year Two 2021 Long-term Debt, Maturities, Repayments of Principal in Year Three 2022 Long-term Debt, Maturities, Repayments of Principal in Year Four 2023 Long-term Debt, Maturities, Repayments of Principal in Year Five Total Long-term Debt, Gross Income Tax Disclosure [Abstract] Income Taxes Income Tax Disclosure [Text Block] Weighted-average remaining lease term (in years) Operating Lease, Weighted Average Remaining Lease Term Weighted-average discount rate (percent) Operating Lease, Weighted Average Discount Rate, Percent Organization, Consolidation and Presentation of Financial Statements [Abstract] Basis of Presentation Basis of 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] Summary of Right-of-Use Asset and Lease Liability Activity and Assumptions Lease, Cost [Table Text Block] Schedule of Future Payments Due Under Operating Leases Lessee, Operating Lease, Liability, Maturity [Table Text Block] Schedule of Future Minimum Lease Payments as Accounted For Prior to Adoption of ASU 2016-02 Schedule of Future Minimum Rental Payments for Operating Leases [Table Text Block] Insurance [Abstract] Regulatory Information Insurance Disclosure [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 (in shares) 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 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) Fair value of warrant liability reclassified to additional paid in capital upon exercise Class Of Warrant Or Right, Fair Value Of Warrant Liability Reclassified To Additional Paid In Capital Upon Exercise Class Of Warrant Or Right, Fair Value Of Warrant Liability Reclassified To Additional Paid In Capital Upon Exercise Change in fair value of warrant liability in current period Class Of Warrant Or Right, Change In Fair Value Of Warrant Liability In Current Period Class Of Warrant Or Right, Change In Fair Value Of Warrant Liability In Current Period 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. 2016-02 Accounting Standards Update 2016-02 [Member] New Accounting Pronouncements [Line Items] New Accounting Pronouncements or Change in Accounting Principle [Line Items] Right-of-use assets Operating Lease, Right-of-Use Asset Lease liabilities Operating Lease, Liability 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 Reinsurance Recoverable for Paid and Unpaid Claims and Claims Adjustments 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 Prior Year Claims and Claims Adjustment Expense Total claims and claim 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 Reinsurance terminations Liability For Unpaid Claims And Claims Adjustment Expense, Claims Paid, Reinsurance Terminations Liability For Unpaid Claims And Claims Adjustment Expense, Claims Paid, Reinsurance Terminations 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 Schedule of Statutory Net Income (Loss), Surplus, Contingency Reserve and Risk-to-Capital Ratio Statutory Accounting Practices Disclosure [Table Text Block] 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. RTC Ratio 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). Reserves for Insurance Claims and Claim Expenses Liability for Future Policy Benefits and Unpaid Claims Disclosure [Text Block] Subsequent Event [Abstract] Subsequent Event [Abstract] 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] 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] Reinsurance Policy, Type [Axis] Reinsurance Policy, Type [Axis] Reinsurance Policy [Domain] Reinsurance Policy [Domain] 2019 ILN Transaction Two Thousand Nineteen ILN Transaction [Member] Two Thousand Nineteen ILN Transaction [Member] Oaktown Re III Ltd [Member] Oaktown Re III Ltd [Member] Oaktown Re III Ltd [Member] Debt Instrument [Axis] Debt Instrument [Axis] Debt Instrument, Name [Domain] Debt Instrument, Name [Domain] 2019 ILN Notes Two Thousand Nineteen ILN Notes [Member] Two Thousand Nineteen ILN Notes [Member] Long-term Debt, Type [Axis] Long-term Debt, Type [Axis] Long-term Debt, Type [Domain] Long-term Debt, Type [Domain] Mortgage-linked Debt Secured Debt [Member] Statistical Measurement [Axis] Statistical Measurement [Axis] Statistical Measurement [Domain] Statistical Measurement [Domain] Maximum Maximum [Member] Subsequent Event [Line Items] Subsequent Event [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 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. Investments, Debt and Equity Securities [Abstract] Investments Investments in Debt and Marketable Equity Securities (and Certain Trading Assets) Disclosure [Text Block] Amortized Cost Debt Securities, Available-for-sale, Maturity, Allocated and Single Maturity Date, Amortized Cost [Abstract] Due in one year or less Debt Securities, Available-for-sale, Maturity, Allocated and Single Maturity Date, within One Year, Amortized Cost Due after one through five years Debt Securities, Available-for-sale, Maturity, Allocated and Single Maturity Date, after One Through Five Years, Amortized Cost Due after five through ten years Debt Securities, Available-for-sale, Maturity, Allocated and Single Maturity Date, after Five Through Ten Years, Amortized Cost Due after ten years Debt Securities, Available-for-sale, Allocated and Single Maturity Date, Maturity, after 10 Years, Amortized Cost Asset-backed securities Debt Securities, Available-for-sale, Maturity, without Single Maturity Date, Amortized Cost Amortized Cost Debt Securities, Available-for-sale, Amortized Cost Fair Value Debt Securities, Available-for-sale, Maturity, Allocated and Single Maturity Date, Fair Value [Abstract] Due in one year or less Debt Securities, Available-for-sale, Maturity, Allocated and Single Maturity Date, within One Year, Fair Value Due after one through five years Debt Securities, Available-for-sale, Maturity, Allocated and Single Maturity Date, after One Through Five Years, Fair Value Due after five through ten years Debt Securities, Available-for-sale, Maturity, Allocated and Single Maturity Date, after Five Through Ten Years, Fair Value Due after ten years Debt Securities, Available-for-sale, Maturity, Allocated and Single Maturity Date, after 10 Years, Fair Value Asset-backed securities Debt Securities, Available-for-sale, Maturity, without Single Maturity Date, Fair Value Fair Value Fixed maturities, available-for-sale, amortized cost Restricted cash Restricted Cash Common stock, par value (in dollars per share) Common Stock, Par or Stated Value Per Share 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 Fair Value Disclosures [Abstract] Fair Value of Financial Instruments Fair Value Disclosures [Text Block] Reinsurance Disclosures [Abstract] Schedule of Effects of Reinsurance Effects of Reinsurance [Table Text Block] Fair Value Measurement Inputs and Valuation Techniques [Table] Fair Value Measurement Inputs and Valuation Techniques [Table] Fair Value Hierarchy and NAV [Axis] Fair Value Hierarchy and NAV [Axis] Fair Value Hierarchy and NAV [Domain] Fair Value Hierarchy and NAV [Domain] Significant Unobservable Inputs (Level 3) Fair Value, Inputs, Level 3 [Member] Valuation Approach and Technique [Axis] Valuation Approach and Technique [Axis] Valuation Approach and Technique [Domain] Valuation Approach and Technique [Domain] Valuation Technique, Option Pricing Model Valuation Technique, Option Pricing Model [Member] Measurement Input Type [Axis] Measurement Input Type [Axis] Measurement Input Type [Domain] Measurement Input Type [Domain] Common stock price Measurement Input, Share Price [Member] Risk free interest rate Measurement Input, Risk Free Interest Rate [Member] Expected life Measurement Input, Expected Term [Member] Expected volatility Measurement Input, Option Volatility [Member] Dividend yield Measurement Input, Expected Dividend Rate [Member] Minimum Minimum [Member] Key Inputs and Assumptions, Valuation Techniques Fair Value Measurement Inputs and Valuation Techniques [Line Items] Warrant liability, measurement input Warrants and Rights Outstanding, Measurement Input Warrant liability, expected life (in years) Warrants and Rights Outstanding, Term Cover page. Document Type Document Type Document Quarterly Report Document Quarterly Report Document Period End Date Document Period End Date Document Transition Report Document Transition Report Entity File Number Entity File Number Entity Registrant Name Entity Registrant Name Entity Central Index Key Entity Central Index Key Current Fiscal Year End Date Current Fiscal Year End Date Document Fiscal Year Focus Document Fiscal Year Focus Document Fiscal Period Focus Document Fiscal Period Focus Amendment Flag Amendment Flag Entity Incorporation, State or Country Code Entity Incorporation, State or Country Code Entity Tax Identification Number Entity Tax Identification Number Entity Address, Address Line One Entity Address, Address Line One Entity Address, City or Town Entity Address, City or Town Entity Address, State or Province Entity Address, State or Province Entity Address, Postal Zip Code Entity Address, Postal Zip Code City Area Code City Area Code Local Phone Number Local Phone Number Title of 12(b) Security Title of 12(b) Security Trading Symbol Trading Symbol Security Exchange Name Security Exchange Name Entity Current Reporting Status Entity Current Reporting Status Entity Interactive Data Current Entity Interactive Data Current Entity Filer Category Entity Filer Category Entity Small Business Entity Small Business Entity Emerging Growth Company Entity Emerging Growth Company Entity Shell Company Entity Shell Company Entity Common Stock, Shares Outstanding Entity Common Stock, Shares Outstanding Reinsurance Reinsurance [Text Block] Ceded Credit Risk [Table] Ceded Credit Risk [Table] Ceded Credit Risk [Line Items] Ceded Credit Risk [Line Items] Ceded risk-in-force Risk In Force, Ceded Risk In Force, Ceded Ceded premiums written Ceded Premiums Written Ceded premiums earned Ceded Premiums Earned Ceded claims and claim 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 Warrants Line of Credit and Related Warrants [Text Block] Line of Credit and Related Warrants [Text Block] Debt Securities, Available-for-sale [Table] Debt Securities, Available-for-sale [Table] Financial Instrument [Axis] Financial Instrument [Axis] Financial Instruments [Domain] Financial Instruments [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] Total bonds Bonds [Member] Short-term investments Short-term Investments [Member] Debt Securities, Available-for-sale [Line Items] Debt Securities, Available-for-sale [Line Items] Gross Unrealized Gains Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax Gross Unrealized Losses Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax Fair value of securities Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Table] Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Table] 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] Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items] Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items] Roll-forward of Level 3 liabilities: Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward] Beginning balance Fair Value, Measurement with Unobservable Inputs Reconciliation, 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 Statutory net income (loss) Statutory Accounting Practices, Statutory Net Income Amount Organization, Basis of Presentation and Summary of Accounting Principles Business Description and Basis of Presentation [Text Block] Statement of Cash Flows [Abstract] Cash flows from operating activities Net Cash Provided by (Used in) Operating Activities [Abstract] 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 (gains) Debt Securities, Available-for-sale, Realized Gain (Loss) Loss (gain) 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 Payment Arrangement, Noncash Expense 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 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 Debt Securities, Available-for-sale 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 Debt Securities, Available-for-sale 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, net of issuance costs Proceeds from Issuance of Common Stock Proceeds from issuance of common stock related to employee equity plans Proceeds, Issuance of Shares, Share-based Payment Arrangement, Including Option Exercised Taxes paid related to net share settlement of equity awards Payment, Tax Withholding, Share-based Payment Arrangement Proceeds from senior note, net Proceeds from Issuance of Senior Long-term Debt Repayments of term loan Repayments of Long-term Debt Payments of debt issuance/modification costs Payments of Debt Issuance Costs Net cash (used in) provided by financing activities Net Cash Provided by (Used in) Financing Activities Net increase (decrease) in cash, cash equivalents and restricted cash Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents, Period Increase (Decrease), Including Exchange Rate Effect Cash, cash equivalents and restricted cash, beginning of period Cash, cash equivalents and restricted cash, end of period Supplemental disclosures of cash flow information Supplemental Cash Flow Information [Abstract] Interest paid Interest Paid, Excluding Capitalized Interest, Operating Activities Income tax (refunded) paid, net Proceeds from Income Tax Refunds Income tax (refunded) paid, net Income Taxes Paid Number of states in which the entity operates Number of States in which Entity Operates Subsequent Events [Abstract] Subsequent Events Subsequent Events [Text Block] Net premiums written Premiums Written, Net [Abstract] Direct Direct Premiums Written Ceded Net premiums written Premiums Written, Net Net premiums earned Premiums Earned, Net [Abstract] Direct Direct Premiums Earned Ceded Net premiums earned Premiums Earned, Net Lessee, Lease, Description [Table] Lessee, Lease, Description [Table] Name of Property [Axis] Name of Property [Axis] Name of Property [Domain] Name of Property [Domain] Corporate Headquarters Corporate Headquarters [Member] Corporate Headquarters [Member] Lessee, Lease, Description [Line Items] Lessee, Lease, Description [Line Items] Number of operating leases related to corporate headquarters and data center facility Number Of Operating Leases, Corporate Office And Data Center Facility Number Of Operating Leases, Corporate Office And Data Center Facility Right-of-use assets obtained in exchange for new operating lease liabilities Right-of-Use Asset Obtained in Exchange for Operating Lease Liability Cash paid for amounts included in the measurement of operating lease liabilities Operating Lease, Initial Direct Cost Expense, over Term Operating lease expense Operating Lease, Expense Operating lease terms Lessee, Operating Lease, Term of Contract Operating lease option to renew, term Lessee, Operating Lease, Renewal Term Change in unrealized investment gains/losses, tax expense (benefit) Other Comprehensive Income (Loss), Securities, Available-for-sale, Tax 2017 ILN Notes Two Thousand Seventeen ILN Notes [Member] Two Thousand Seventeen ILN Notes [Member] 2018 ILN Notes Two Thousand Eighteen ILN Notes [Member] Two Thousand Eighteen ILN Notes [Member] Oaktown Re Ltd Oaktown Re Ltd [Member] Oaktown Re Ltd [Member] ILN Transactions ILN Transactions [Member] ILN Transactions [Member] 2017 ILN Transaction Two Thousand Seventeen ILN Transaction [Member] Two Thousand Seventeen ILN Transaction [Member] 2018 ILN Transaction Two Thousand Eighteen ILN Transaction [Member] Two Thousand Eighteen ILN Transaction [Member] QSR Transactions QSR Transactions [Member] QSR Transactions [Member] 2018 QSR Transaction Two Thousand Eighteen QSR Transaction [Member] Two Thousand Eighteen QSR Transaction [Member] Risk Written Policies in 2018 Eligible Policies, Pool Four [Member] Eligible Policies, Pool Four [Member] Risk Written Policies in 2019 Eligible Policies, Pool Five [Member] Eligible Policies, Pool Five [Member] 2016 QSR Transaction Two Thousand Sixteen QSR Transaction [Member] Two Thousand Sixteen QSR Transaction [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] 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 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 ceded under QSR Transaction Reinsurance Retention Policy, Reinsured Risk, Percentage Percent of premiums earned under 2018 QSR Transaction Premiums Earned, Percent Of Risk Premiums Earned, Percent Of Risk Previously ceded primary RIF recaptured Previously Ceded Primary Risk-In-Force Recaptured Previously Ceded Primary Risk-In-Force Recaptured 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 Schedule of Available-for-sale Securities [Table] Schedule of Available-for-sale Securities [Table] U.S. Treasury securities and obligations of U.S. government agencies Cash and investments held with various state insurance departments Cash, Cash Equivalents, and Short-term Investments Unrealized loss position, accumulated loss Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss Unrealized loss position, 12 months or greater Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss Other-than-temporary impairment Other-than-temporary Impairment Loss, Debt Securities, Available-for-sale Effective income tax rate on pre-tax income or loss Effective Income Tax Rate Reconciliation, Percent Schedule of Future Principal Payments Schedule of Maturities of Long-term Debt [Table Text Block] Number of securities, less than 12 months Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Number of Positions Fair value, less than 12 months Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months Unrealized losses, less than 12 months Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss Number of securities,12 months or greater Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Number of Positions Fair value, 12 months or greater Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer Unrealized losses, 12 months or greater Number of securities, total Debt Securities, Available-for-sale, Unrealized Loss Position, Number of Positions Fair value Debt Securities, Available-for-sale, Unrealized Loss Position Unrealized Losses Future Payment Due Under Operating Leases Lessee, Operating Lease, Liability, Payment, Due [Abstract] 2019 Lessee, Operating Lease, Liability, Payments, Remainder of Fiscal Year 2020 Lessee, Operating Lease, Liability, Payments, Due Year Two 2021 Lessee, Operating Lease, Liability, Payments, Due Year Three 2022 Lessee, Operating Lease, Liability, Payments, Due Year Four 2023 Lessee, Operating Lease, Liability, Payments, Due Year Five Total undiscounted lease payments Lessee, Operating Lease, Liability, Payments, Due Less effects of discounting Lessee, Operating Lease, Liability, Undiscounted Excess Amount Present value of lease payments Liability for Claims and Claims Adjustment Expense [Table] Liability for Claims and Claims Adjustment Expense [Table] 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 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 Favorable prior year development 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 Reconciliation of Liability for Insurance Claims and Claim Expenses Schedule of Liability for Unpaid Claims and Claims Adjustment Expense [Table Text Block] Schedule of Earnings per Share, Basic and Diluted Schedule of Earnings Per Share, Basic and Diluted [Table 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 Measurement Inputs and Valuation Techniques [Table Text Block] Schedule of Fair Values and Gross Unrealized Gains and Losses Debt Securities, Available-for-sale [Table Text Block] Schedule of Investments by Industry Group Investments Classified By Issuer Industry Group [Table Text Block] Investments Classified By Issuer Industry Group [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 Components of Net Investment Income Investment Income [Table Text Block] Schedule of Net Realized Investment Gains (Losses) Realized Gain (Loss) on Investments [Table Text Block] Debt Debt Disclosure [Text Block] Gross realized investment gains Debt Securities, Available-for-sale, Realized Gain Gross realized investment losses Debt Securities, Available-for-sale, Realized Loss Net realized investment losses Income Statement [Abstract] Net unrealized (losses) gains in accumulated other comprehensive income, tax (benefit) expense Other Comprehensive Income (Loss), Securities, Available-for-Sale, Unrealized Holding Gain (Loss) 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 Debt Securities By Industry [Axis] Debt Securities By Industry [Axis] Debt Securities By Industry [Axis] Debt Securities By Industry [Domain] Debt Securities By Industry [Domain] [Domain] for Debt Securities By Industry [Axis] Financial Financial, Industry Group [Member] Financial, Industry Group [Member] Consumer Consumer, Industry Group [Member] Consumer, Industry Group [Member] Communications Communications, Industry Group [Member] Communications, Industry Group [Member] Utilities Utilities, Industry Group [Member] Utilities, Industry Group [Member] Industrial Industrial, Industry Group [Member] Industrial, Industry Group [Member] Technology Technology, Industry Group [Member] Technology, Industry Group [Member] Energy Energy, Industry Group [Member] Energy, Industry Group [Member] Other Other, Industry Group [Member] Other, Industry Group [Member] Debt Securities By Industry [Line Items] Debt Securities By Industry [Line Items] Debt Securities By Industry [Line Items] Corporate debt securities as component of total (percent) Debt Securities, Corporate, Component Of Total. Percentage Debt Securities, Corporate, Component Of Total. Percentage Earnings per Share (EPS) Earnings Per Share [Text Block] Revenues Revenues [Abstract] Net premiums earned Net investment income Net Investment Income Net realized investment (losses) gains Gain (Loss) on Investments Other revenues Other Income 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] (Loss) gain 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 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] Weighted average common shares outstanding Weighted Average Number of Shares Outstanding Reconciliation [Abstract] Dilutive weighted average shares outstanding (in shares) Comprehensive income: Comprehensive Income (Loss), Net of Tax, Attributable to Parent [Abstract] Other comprehensive income (loss), net of tax: Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Parent [Abstract] Unrealized gains (losses) in accumulated other comprehensive income, net of tax expense (benefit) of $3,662 and ($2,879) for the three months ended June 30, 2019 and 2018 and $7,615 and ($3,304) for the six months ended June 30, 2019 and 2018, respectively Other Comprehensive Income (Loss), Securities, Available-for-Sale, Unrealized Holding Gain (Loss) Arising During Period, after Tax Reclassification adjustment for realized losses (gains) included in net income, net of tax (benefit) expense of ($24) and $12 for the three months ended June 30, 2019 and 2018 and ($63) and $10 for the six months ended June 30, 2019 and 2018, 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 Leases Lessee, Operating Leases [Text Block] Schedule of Long-term Debt Instruments [Table] Schedule of Long-term Debt Instruments [Table] Credit Facility [Axis] Credit Facility [Axis] Credit Facility [Domain] Credit Facility [Domain] Revolving Credit Facility Revolving Credit Facility [Member] Secured Debt Senior Secured Debt Senior Secured Debt [Member] Senior Secured Debt [Member] 2018 Term Loan Senior Secured Term Loan 2018 [Member] Senior Secured Term Loan 2018 [Member] 2018 Revolving Credit Facility Secured Revolving Credit Facility 2018 [Member] Secured Revolving Credit Facility 2018 [Member] 2015 Term Loan Credit Agreement Amendment [Member] Credit Agreement Amendment [Member] Variable Rate [Axis] Variable Rate [Axis] Variable Rate [Domain] Variable Rate [Domain] Base Rate Base Rate [Member] Eurodollar Eurodollar [Member] Debt Instrument [Line Items] Debt Instrument [Line Items] Debt instrument face amount Debt Instrument, Face Amount Debt instrument term (years) Debt Instrument, Term Credit facility borrowing capacity Line of Credit Facility, Maximum Borrowing Capacity Variable rate floor (percent) Debt Instrument, Variable Interest Rate Floor Debt Instrument, Variable Interest Rate Floor Basis spread on variable rate (percent) Debt Instrument, Basis Spread on Variable Rate Interest rate during period (percent) Debt Instrument, Interest Rate During Period Frequency of periodic payment Debt Instrument, Frequency of Periodic Payment Periodic payment of principal Debt Instrument, Periodic Payment, Principal Term loan Borrowings outstanding Long-term Line of Credit Interest expense Unamortized issuance costs Debt Instrument, Unamortized Discount (Premium) and Debt Issuance Costs, Net Commitment fee (percent) Line of Credit Facility, Unused Capacity, Commitment Fee Percentage Commitment fees in interest expense Line of Credit Facility, Commitment Fee Amount Debt issuance costs Debt Issuance Costs, Gross Interest expense from amortization of debt issuance costs Amortization of Debt Issuance Costs Remaining deferred issuance costs, net of accumulated amortization Debt Issuance Costs, Line of Credit Arrangements, Net 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 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 Fair Value, Recurring and Nonrecurring [Table] Fair Value, Recurring and Nonrecurring [Table] Measurement Frequency [Axis] Measurement Frequency [Axis] Measurement Frequency [Domain] Measurement Frequency [Domain] Recurring Fair Value, Recurring [Member] 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] 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] 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