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Value, Inputs, Level 2 [Member] Due after five through ten years Debt Securities, Available-for-Sale, Amortized Cost, Maturity, Allocated and Single Maturity Date, after Year 5 Through 10 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 Prior years Liability for Unpaid Claims and Claims Adjustment Expense, Claims Paid, Prior Years Percentage of Amount Assumed to Net SEC Schedule, 12-17, Insurance Companies, Reinsurance, Premium, Percentage Assumed to Net Options forfeited (in shares) Share-based Compensation Arrangement by Share-based Payment Award, Options, Forfeitures in Period After March 1, 2025 After March 1, 2025 [Member] After March 1, 2025 NMIC NMIC [Member] NMIC [Member] Shareholders' equity Equity [Abstract] Total assets Assets, Fair Value Disclosure Diluted EPS Net Income (Loss) Available to Common 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Eligible Policies, Pool Five [Member] Risk free interest rate Measurement Input, Risk Free Interest Rate [Member] Other Deferred Tax Liabilities, Other Operating lease liabilities Present value of lease payments Operating Lease, Liability Net deferred income tax (liability) Deferred Tax Liabilities, Net 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 Previously Ceded Primary Risk-In-Force Recaptured Previously Ceded Primary Risk-In-Force Recaptured Previously Ceded Primary Risk-In-Force Recaptured Debt Instrument [Line Items] Debt Instrument [Line Items] Reserve for Insurance Claims and Claims Expenses Liability Reserve Estimate, Policy [Policy Text Block] Statement of Comprehensive Income [Abstract] Statement of Comprehensive Income [Abstract] Total shareholders' equity Beginning balance Ending balance Stockholders' Equity 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Cash and Cash Equivalents Cash and Cash Equivalents, Policy [Policy Text Block] Total revenues Revenues Class of Stock [Axis] Class of Stock [Axis] Current year Current Year Claims and Claims Adjustment Expense Income tax expense Total income tax expense Income tax expense (benefit) Income Tax Expense (Benefit) Income taxes (refunded) paid Income Taxes Paid, Net Cash and cash equivalents (including restricted cash of $5,555 and $2,662 as of December 31, 2020 and December 31, 2019, respectively) Cash, cash equivalents and restricted cash, beginning of period Cash, cash equivalents and restricted cash, end of period Cash and cash equivalents Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents Contribution amount Defined Contribution Plan, Employer Discretionary Contribution Amount Software and Equipment Property, Plant and Equipment, Policy [Policy Text Block] Debt Securities, Available-for-sale [Table] Debt Securities, Available-for-sale [Table] Indefinite-lived Intangible Assets, Major Class Name [Domain] Indefinite-lived Intangible Assets, Major Class Name [Domain] Total liabilities Financial and Nonfinancial Liabilities, Fair Value Disclosure Diluted (in dollars per share) Diluted earnings per share (in dollars per share) Earnings Per Share, Diluted Local Phone Number Local Phone Number Premiums Receivable Premiums Receivable, Basis of Accounting, Policy [Policy Text Block] Dividends, restriction with regards to capital surplus (in percent) Dividends, restriction with regards to capital surplus Ordinary Dividends, Restriction with Regards to Capital Surplus This concept represents the maximum percentage of surplus as of the prior year that an insurer may pay out in ordinary dividends without prior approval of the Wisconsin Office of the Commissioner of Insurance under Wisconsin law. Reserve for prior year insurance claims and claims expense Liability for Prior Year Claims and Claims Adjustment Expense Liability for Prior Year Claims and Claims Adjustment Expense Loss carry forwards subject to expiration Deferred Tax Assets, Operating Loss Carryforwards, Subject to Expiration Cumulative Effect, Period of Adoption [Domain] Cumulative Effect, Period of Adoption [Domain] Schedule of Stock by Class [Table] Schedule of Stock by Class [Table] Aggregate intrinsic value of options exercised Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercises in Period, Intrinsic Value Current Reinsurance Coverage Current Reinsurance Coverage Current Reinsurance Coverage Warrant liability, measurement input Warrants and Rights Outstanding, Measurement Input Schedule of Identifiable Intangible Assets and Goodwill Schedule of Indefinite-Lived Intangible Assets [Table Text Block] Business Combinations, Goodwill and Intangible Assets Goodwill and Intangible Assets, Policy [Policy Text Block] 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] Net investment income Investment Income, Net Entity Address, Address Line One Entity Address, Address Line One SEC Schedule, 12-17, Insurance Companies, Reinsurance [Abstract] SEC Schedule, 12-17, Insurance Companies, Reinsurance [Abstract] Entity Emerging Growth Company Entity Emerging Growth Company SEC Schedule, 12-17, Insurance Companies, Reinsurance [Table] SEC Schedule, 12-17, Insurance Companies, Reinsurance [Table] Intangible assets Indefinite-lived Intangible Assets (Excluding Goodwill) Schedule of Finite-Lived Intangible Assets [Table] Schedule of Finite-Lived Intangible Assets [Table] Deferred Deferred Income Tax Expense (Benefit) Accrued investment income Accrued Investment Income Receivable Credit facility borrowing capacity Line of Credit Facility, Maximum Borrowing Capacity Due from affiliates, net Due from Affiliates IRS Internal Revenue Service (IRS) [Member] Award Type [Axis] Award Type [Axis] Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items] Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items] Weighted Average Grant Date Fair Value per Share Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value [Abstract] Fair value of shares vested Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Vested in Period, Fair Value Maximum Maximum [Member] Reinsurance balances, net Increase (Decrease) in Reinsurance Assets and Liabilities Increase (Decrease) in Reinsurance Assets and Liabilities Share-based compensation Deferred Tax Assets, Tax Deferred Expense, Compensation and Benefits, Share-based Compensation Cost Net realized investment gains Net realized investment (losses) gains Net realized investment gains Gain (Loss) on Investments Restricted cash Restricted Cash Purchase of short-term investments Payments to Acquire Short-term Investments Accounts payable and accrued expenses Accounts Payable and Accrued Liabilities Retained Earnings (Accumulated Deficit) Retained Earnings [Member] Claims and claim expenses incurred: Liability for Unpaid Claims and Claims Adjustment Expense, Incurred Claims [Abstract] Mortgage insurance risk in force Mortgage Insurance Risk in Force This concept represents the risk in force (an estimate of the maximum loss exposure that an entity has at any point in time). Effective income tax rate Effective Income Tax Rate Reconciliation, Percent 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] Summary of Accounting Principles Significant Accounting Policies [Text Block] Net cash (used in) investing activities Net Cash Provided by (Used in) Investing Activities Schedule of Share-based Compensation Arrangements by Share-based Payment Award [Table] Schedule of Share-based Compensation Arrangements by Share-based Payment Award [Table] Warrant liability, at fair value Warrants and Rights Outstanding Award Type [Domain] Award Type [Domain] Service expenses Other Nonoperating Expense Initial Reinsurance Coverage Initial Reinsurance Coverage Initial Reinsurance Coverage Financial Financial, Industry Group [Member] Financial, Industry Group [Member] Corporate debt securities Corporate Debt Securities [Member] Trading Symbol Trading Symbol 2018 QSR Transaction Two Thousand Eighteen QSR Transaction [Member] Two Thousand Eighteen QSR Transaction [Member] Weighted average common shares outstanding Weighted Average Number of Shares Outstanding Reconciliation [Abstract] Profit commission Reinsurance Profit Commission Reinsurance Profit Commission Risk Written Policies in 2018 Eligible Policies, Pool Four [Member] Eligible Policies, Pool Four [Member] Software and Equipment Property, Plant and Equipment Disclosure [Text Block] Weighted average remaining contractual life of RSUs outstanding Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Outstanding, Weighted Average Remaining Contractual Terms Commitment fee (in percent) Line of Credit Facility, Unused Capacity, Commitment Fee Percentage Proceeds from issuance of common stock related to employee equity plans Proceeds, Issuance of Shares, Share-based Payment Arrangement, Including Option Exercised 2016 QSR Transaction Two Thousand Sixteen QSR Transaction [Member] Two Thousand Sixteen QSR Transaction [Member] Unearned premium reserve Deferred Tax Assets, Tax Deferred Expense, Reserves and Accruals, Unearned Premiums Reserve Earnings per Share Earnings Per Share [Text Block] 2021 QSR Transaction Two Thousand Twenty One QSR Transaction [Member] Two Thousand Twenty One QSR Transaction Organization, Consolidation and Presentation of Financial Statements [Abstract] Organization, Consolidation and Presentation of Financial Statements [Abstract] Reconciliation of Liability for Insurance Claims and Claims Expenses Schedule of Liability for Unpaid Claims and Claims Adjustment Expense [Table Text Block] Equipment Equipment [Member] Federal statutory income tax rate Effective Income Tax Rate Reconciliation, at Federal Statutory Income Tax Rate, Percent 2019 ILN Transaction 2019 ILN [Member] 2019 ILN [Member] Entity Shell Company Entity Shell Company Fair Value Measurement Inputs and Valuation Techniques [Line Items] Fair Value Measurement Inputs and Valuation Techniques [Line Items] Recurring Fair Value, Recurring [Member] Prepaid reinsurance premiums Prepaid Reinsurance Premiums Net premiums earned Net premiums earned Premiums Earned, Net Options expired (in dollars per share) Share-based Compensation Arrangements by Share-based Payment Award, Options, Expirations in Period, Weighted Average Exercise Price Income Tax Contingency [Table] Income Tax Contingency [Table] Recent Accounting Pronouncements New Accounting Pronouncements, Policy [Policy Text Block] Entity Public Float Entity Public Float Statement of Financial Position [Abstract] Statement of Financial Position [Abstract] Statutory Accounting Practices [Line Items] Statutory Accounting Practices [Line Items] Year 2 Short-duration Insurance Contracts, Historical Claims Duration, Year Two