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Asset-backed securities Debt Securities, Available-for-sale, Maturity, without Single Maturity Date, Amortized Cost Reinsurance recoverable Reinsurance Recoverables, Gross Fair Value by Liability Class [Domain] Fair Value by Liability Class [Domain] Beginning balance (in shares) Ending balance (in shares) Shares, Outstanding Insurance claims and claim expenses Policyholder Benefits and Claims Incurred, Net, Property, Casualty and Liability Variable rate floor (in percent) Debt Instrument, Variable Interest Rate Floor Debt Instrument, Variable Interest Rate Floor U.S. Treasury securities and obligations of U.S. government agencies U.S. Treasury securities and obligations of U.S. government agencies US Treasury and Government [Member] Common stock, par value (in dollars per share) Common Stock, Par or Stated Value Per Share Valuation Approach and Technique [Domain] Valuation Approach and Technique [Domain] Other comprehensive income, net of tax: Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Parent [Abstract] Unearned premiums Unearned Premiums Liability Class [Axis] Liability Class [Axis] Share-based compensation expense APIC, Share-based Payment Arrangement, Increase for Cost Recognition Measurement Frequency [Domain] Measurement Frequency [Domain] Investments Investment, Policy [Policy Text Block] Accrued investment income Increase (Decrease) in Accrued Investment Income Receivable Valuation technique, option pricing model Valuation Technique, Option Pricing Model [Member] Statement [Line Items] Statement [Line Items] Forecast Forecast [Member] Earnings per share Earnings Per Share, Basic and Diluted [Abstract] Debt instrument term (years) Debt Instrument, Term Measurement Input Type [Domain] Measurement Input Type [Domain] Statement [Table] Statement [Table] Statistical Measurement [Axis] Statistical Measurement [Axis] Reinsurance Reinsurance [Text Block] Credit Facility [Axis] Credit Facility [Axis] Deferred income taxes Deferred Income Taxes and Tax Credits Exercise price of warrants (in dollars per warrant) Class of Warrant or Right, Exercise Price of Warrants or Rights 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 Amount outstanding Line of Credit Facility, Fair Value of Amount Outstanding Beginning balance, net of reinsurance recoverables Reserve at end of period, net of reinsurance recoverables Liability for Unpaid Claims and Claims Adjustment Expense, Net Prior to June 1, 2022 Prior to June 1, 2022 [Member] Prior to June 1, 2022 Entity Small Business Entity Small Business Increase (Decrease) in Stockholders' Equity [Roll Forward] Increase (Decrease) in Stockholders' Equity [Roll Forward] Number of shares sold (in shares) Sale of Stock, Number of Shares Issued in Transaction Debt Debt Disclosure [Text Block] Fair Value Hierarchy and NAV [Domain] Fair Value Hierarchy and NAV [Domain] Energy Energy, Industry Group [Member] Energy, Industry Group [Member] Proceeds from issuance of common stock related to public offering, net of issuance costs Proceeds from Issuance of Common Stock Proceeds from redemptions, maturities and sale of fixed-maturity investments, available-for-sale Proceeds from Sale and Maturity of Debt Securities, Available-for-sale Amendment Flag Amendment Flag Schedule of earnings per share, basic and diluted Schedule of Earnings Per Share, Basic and Diluted [Table Text Block] Expected volatility Measurement Input, Option Volatility [Member] Beginning balance Ending balance Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Liability Value Debt Issuance costs Debt Issuance Costs, Line of Credit Arrangements, Gross 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. Borrowings outstanding Long-term Line of Credit Ceded Credit Risk, Reinsurer [Axis] Ceded Credit Risk, Reinsurer [Axis] Net cash provided by operating activities Net Cash Provided by (Used in) Operating Activities Favorable prior year development Prior years Prior Year Claims and Claims Adjustment Expense Entity Central Index Key Entity Central Index Key Measurement Frequency [Axis] Measurement Frequency [Axis] Financial Instruments [Domain] Financial Instruments [Domain] Aggregate dividend capacity Statutory Accounting Practices, Statutory Amount Available for Dividend Payments Statutory surplus Statutory Accounting Practices, Statutory Capital and Surplus, Balance 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 Over-allotment option to purchase shares (in percent) Sale of Stock, Over-Allotment Option, Percentage Sale of Stock, Over-Allotment Option, Percentage Fair value, 12 months or greater Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer Senior debt Senior Notes [Member] 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 Fannie Mae Eligible Policies, Pool Two [Member] Eligible Policies, Pool Two [Member] Subsequent Event Subsequent Events [Text Block] NMIC and Re One combined NMic and Re one Combined [Member] NMic and Re one Combined [Member] Ceding commission earned Reinsurance Ceding Commission Earned Reinsurance Ceding Commission Earned Diluted net income Net Income (Loss) Attributable to Parent, Diluted Segments [Domain] Segments [Domain] (Gain) loss from change in fair value of warrant liability Fair Value Adjustment of Warrants Fixed maturities, available-for-sale, amortized cost Amortized Cost Debt Securities, Available-for-sale, Amortized Cost Gross unrealized gains Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax Statement of Cash Flows [Abstract] Statement of Cash Flows [Abstract] Annual risk premium payments, capped amount Risk Premium Payments, Annual Risk Premium Payments, Annual Ceded Credit Risk [Line Items] Ceded Credit Risk [Line Items] Dilutive effect of issuable shares (in shares) Weighted Average Number Diluted Shares Outstanding Adjustment 2018 Term loan Senior Secured Term Loan 2018 [Member] Senior Secured Term Loan 2018 [Member] Dividend yield Measurement Input, Expected Dividend Rate [Member] Entity Common Stock, Shares Outstanding Entity Common Stock, Shares Outstanding 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. Regulatory Information Insurance Disclosure [Text Block] Schedule of components of net investment income Investment Income [Table Text Block] Cash flows from financing activities Net Cash Provided by (Used in) Financing Activities [Abstract] Reinsurance coverage amount amortized (as a percent) Reinsurance Agreement, Optional Termination Right, Percent Of Reinsurance Coverage Threshold Reinsurance Agreement, Optional Termination Right, Percent Of Reinsurance Coverage Threshold Reserve for insurance claims and claim expenses Increase (Decrease) in Liability for Claims and Claims Adjustment Expense Reserve Other liabilities Other Liabilities Common stock: class A shares issued related to public offering Stock Issued During Period, Value, New Issues Cash, cash equivalents and short-term investments Cash and Cash Equivalents, Fair Value Disclosure Total assets Assets Scenario [Axis] Scenario [Axis] Premiums receivable Premiums Receivable, Net General corporate purposes Corporate Segment [Member] Title of 12(b) Security Title of 12(b) Security Reserves for Insurance Claims and Claim Expenses Liability for Future Policy Benefits and Unpaid Claims Disclosure [Text Block] Subsequent Event Type [Axis] Subsequent Event Type [Axis] Unrealized gains in accumulated other comprehensive income, net of tax expense of $2,494 and $1,376 for the three months ended September 30, 2020 and 2019, respectively, and $7,655 and $8,991 for the nine months ended September 30, 2020 and 2019, respectively OCI, Debt Securities, Available-for-Sale, Unrealized Holding Gain (Loss), before Adjustment, after Tax Investments, Debt and Equity Securities [Abstract] Investments, Debt and Equity Securities [Abstract] Organization, Basis of Presentation and Summary of Accounting Principles Business Description and Basis of Presentation [Text Block] Net unrealized (losses) gains in accumulated other comprehensive income, tax (benefit) expense OCI, Debt Securities, Available-for-Sale, Unrealized Holding Gain (Loss), before Adjustment, Tax Common stock price Measurement Input, Share Price [Member] Interest expense Interest Expense Net proceeds of sale of stock Sale of Stock, Consideration Received on Transaction Short-term investments Short-term Investments [Member] 2018 ILN Transaction 2018 ILN [Member] 2018 ILN [Member] Risk written policies in 2020 Eligible Policies, Pool Six [Member] Eligible Policies, Pool Six Amortized Cost Debt Securities, Available-for-sale, Maturity, Allocated and Single Maturity Date, Amortized Cost, Rolling Maturity [Abstract] Total liabilities Liabilities Insurance [Abstract] Insurance [Abstract] 2020 Revolving credit facility Secured Revolving Credit Facility 2020 [Member] Secured Revolving Credit Facility 2020 Valuation Approach and Technique [Axis] Valuation Approach and Technique [Axis] Fair Value Debt Securities, Available-for-sale, Unrealized Loss Position Mortgage insurance-linked notes Mortgage Insurance-Linked Notes [Member] Mortgage Insurance-Linked Notes Debt Securities By Industry [Axis] Debt Securities By Industry [Axis] Debt Securities By Industry [Axis] 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 Quoted Prices in Active Markets for Identical Assets (Level 1) Fair Value, Inputs, Level 1 [Member] Fair Value, Recurring and Nonrecurring [Table] Fair Value, Recurring and Nonrecurring [Table] Number of states in which the entity operates Number of States in which Entity Operates Fair value, less than 12 months Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months Gross realized investment gains Debt Securities, Available-for-sale, Realized Gain Anticipated payment related to annual operating expenses Anticipated Operating Expense Payments, Annual Amount of anticipated payments related to operating expenses of counterparty. Debt Instrument [Axis] Debt Instrument [Axis] Additional Paid-in Capital Additional Paid-in Capital [Member] Other assets Other Assets Expected life Measurement Input, Expected Term [Member] Corporate debt securities as component of total (percent) Debt Securities, Corporate, Component Of Total. Percentage Debt Securities, Corporate, Component Of Total. Percentage Class of Stock [Line Items] Class of Stock [Line Items] Adjustments to reconcile net income to net cash provided by operating activities: Adjustments to Reconcile Net Income (Loss) to Cash Provided by (Used in) Operating Activities [Abstract] Number of securities, less than 12 months Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Number of Positions ILN transactions ILN Transactions [Member] ILN Transactions [Member] Number of securities,12 months or greater Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Number of Positions Common stock, outstanding (in shares) Common Stock, Shares, Outstanding Income Tax Disclosure [Abstract] Income Tax Disclosure [Abstract] Total claims and claim expenses paid Liability for Unpaid Claims and Claims Adjustment Expense, Claims Paid Revolving credit facility Revolving Credit Facility [Member] Income before income taxes Income (Loss) from Continuing Operations before Income Taxes, Noncontrolling Interest Warrants Line of Credit and Related Warrants [Text Block] Line of Credit and Related Warrants [Text Block] Due after ten years Debt Securities, Available-for-sale, Maturity, Allocated and Single Maturity Date, Rolling after 10 Years, Fair Value Subsequent Event Subsequent Event [Member] Common stock, authorized (in shares) Common Stock, Shares Authorized Premiums receivable Increase (Decrease) in Premiums Receivable Schedule of ILN transactions Schedule of respective coverages and retentions of the ILN transactions [Table Text Block] Schedule of respective coverages and retentions of the ILN transactions [Table Text Block] Debt instrument covenant, maximum debt-to-total capitalization ratio Debt Instrument, Covenant Terms, Debt to Total Capitalization Ratio, Maximum Debt Instrument, Covenant Terms, Debt to Total Capitalization Ratio, Maximum Due in one year or less Debt Securities, Available-for-sale, Maturity, Allocated and Single Maturity Date, Rolling within One Year, Amortized Cost Prepaid expenses Prepaid Expense Income Statement [Abstract] Income Statement [Abstract] Accumulated Other Comprehensive Income AOCI Attributable to Parent [Member] Schedule of investments by maturity Investments Classified by Contractual Maturity Date [Table Text Block] Other assets Increase (Decrease) in Prepaid Expense and Other Assets Over-allotment option Over-Allotment Option [Member] Accrued interest receivable Interest Receivable Number of votes per common share Number Of Votes Per Share Of Common Stock Number Of Votes Per Share Of Common Stock Capitalized issuance cost and issue discounts Debt Instrument, Unamortized Discount (Premium) and Debt Issuance Costs, Net Total claims and claim expenses incurred Liability for Unpaid Claims and Claims Adjustment Expense, Incurred Claims Initial First Layer Retained Loss Initial First Layer Retained Loss Initial First Layer Retained Loss Consumer Consumer, Industry Group [Member] Consumer, Industry Group [Member] 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 Public stock offering Public Stock Offering [Member] Public Stock Offering Deductible on policy Mortgage Pool Insurance, Claim Deductible Mortgage Pool Insurance, Claim Deductible Comprehensive income Comprehensive Income (Loss), Net of Tax, Attributable to Parent 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 Prior to March 1, 2025 Prior To March 1, 2025 [Member] Prior To March 1, 2025 Schedule of Deferred Compensation Arrangement with Individual, Excluding Share-based Payments and Postretirement Benefits, by Title of Individual and by Type of Deferred Compensation [Table] Schedule of Deferred Compensation Arrangement with Individual, Excluding Share-based Payments and Postretirement Benefits, by Title of Individual and by Type of Deferred Compensation [Table] Risk premiums paid Reinsurance Retention, Risk Premiums Paid Reinsurance Retention, Risk Premiums Paid Scenario [Domain] Scenario [Domain] Legal Entity [Axis] Legal Entity [Axis] Counterparty Name [Domain] Counterparty Name [Domain] Software and equipment Payments to Acquire Property, Plant, and Equipment City Area Code City Area Code Document Period End Date Document Period End Date Unrealized loss position, accumulated loss Unrealized Losses Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss Technology Technology, Industry Group [Member] Technology, Industry Group [Member] Prepaid expenses Increase (Decrease) in Prepaid Expense Proceeds from senior secured notes Proceeds from Issuance of Senior Long-term Debt Long-term Debt, Type [Domain] Long-term Debt, Type [Domain] Industrial Industrial, Industry Group [Member] Industrial, Industry Group [Member] Share-based compensation expense Share-based Payment Arrangement, Noncash Expense Gain from change in fair value of warrant liability Gain From Change In Fair Value of Warrant Liability Gain From Change In Fair Value of Warrant Liability Entity [Domain] Entity [Domain] 2018 Revolving credit facility Secured Revolving Credit Facility 2018 [Member] Secured Revolving Credit Facility 2018 [Member] Taxes paid related to net share settlement of equity awards Payment, Tax Withholding, Share-based Payment Arrangement Cover page. Cover [Abstract] Base rate Base Rate [Member] Percent of premiums earned under 2018 QSR Transaction Premiums Earned, Percent Of Risk Premiums Earned, Percent Of Risk Measurement Input Type [Axis] Measurement Input Type [Axis] Schedule of fair values and gross unrealized gains and losses Debt Securities, Available-for-sale [Table Text Block] Debt Long-term Debt Fair Value Disclosures [Abstract] Fair Value Disclosures [Abstract] Net amortization of premium on investment securities Accretion (Amortization) of Discounts and Premiums, Investments Liability for Unpaid Claims and Claims Adjustment Expense [Roll Forward] Liability for Unpaid Claims and Claims Adjustment Expense [Roll Forward] Eligible policies, pool one Eligible Policies, Pool One [Member] Eligible Policies, Pool One [Member] Reclassification adjustment for realized losses (gains) included in net income, net of tax (benefit) expense of ($1) and $17 for the three months ended September 30, 2020 and 2019, respectively, and ($258) and ($46) for the nine months ended September 30, 2020 and 2019, respectively Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI for Sale of Securities, Net of Tax Fixed maturities, available-for-sale, at fair value (amortized cost of $1,624,970 and $1,113,779 as of September 30, 2020 and December 31, 2019, respectively) Fair Value Fair Value Fair value of securities Debt Securities, Available-for-sale Total expenses Costs and Expenses Equity Components [Axis] Equity Components [Axis] Debt Instrument, Name [Domain] Debt Instrument, Name [Domain] Due after one through five years Debt Securities, Available-for-sale, Maturity, Allocated and Single Maturity Date, Rolling after One Through Five Years, Amortized Cost Minimum Minimum [Member] Net premiums written Premiums Written, Net Reinsurance funds withheld Funds Held under Reinsurance Agreements, Liability Ceded Ceded premiums earned Ceded Premiums Earned Asset-backed securities Asset-backed Securities [Member] Entity Interactive Data Current Entity Interactive Data Current Revenues Revenues [Abstract] Fair Value of Financial Instruments Fair Value Disclosures [Text Block] Cash flows from operating activities Net Cash Provided by (Used in) Operating Activities [Abstract] Common Stock Stockholders' Equity Note Disclosure [Text Block] Liability for Claims and Claims Adjustment Expense [Line Items] Liability for Claims and Claims Adjustment Expense [Line Items] Current year Liability for Unpaid Claims and Claims Adjustment Expense, Claims Paid, Current Year 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). Depreciation and amortization Depreciation, Amortization and Accretion, Net Reinsurance recoverable on loss reserve Reinsurance recoverable on unpaid claims Less reinsurance recoverables Add reinsurance recoverables Reinsurance Recoverable for Paid and Unpaid Claims and Claims Adjustments Entity Registrant Name Entity Registrant Name Subsequent Event Type [Domain] Subsequent Event Type [Domain] Statement of Stockholders' Equity [Abstract] Statement of Stockholders' Equity [Abstract] Claims and claim expenses paid: Liability for Unpaid Claims and Claims Adjustment Expense, Claims Paid [Abstract] Debt Securities By Industry [Line Items] Debt Securities By Industry [Line Items] Debt Securities By Industry [Line Items] Reinsurance Policy, Type [Axis] Reinsurance Policy, Type [Axis] Third-party reinsurers Third-Party Reinsurers [Member] Third-Party Reinsurers [Member] Underwriting and operating expenses Other Cost and Expense, Operating Warrants exercised (in shares) Class of Warrant or 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losses Net realized investment (losses) gains Debt Securities, Available-for-sale, Realized Gain (Loss) Fair Value Debt Securities, Available-for-sale, Maturity, Allocated and Single Maturity Date, Fair Value [Abstract] Fair Value Measurement Inputs and Valuation Techniques [Table] Fair Value Measurement Inputs and Valuation Techniques [Table] Public stock offering and over allotment option Public Stock Offering and Over Allotment Option [Member] Public Stock Offering and Over Allotment Option Debt Securities, Available-for-sale [Line Items] Debt Securities, Available-for-sale [Line Items] Schedule of key inputs and assumptions in option-pricing model Fair Value Measurement Inputs and Valuation Techniques [Table Text Block] Effects of Reinsurance [Line Items] Effects of Reinsurance [Line Items] Other comprehensive income, net of tax Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Parent Document Transition Report Document Transition Report Ceded claims and claim expenses Reinsurance Ceded Claims and Claims Expenses Reinsurance Ceded Claims and Claims Expenses Debt Instrument, Redemption, Period [Axis] Debt Instrument, Redemption, Period [Axis] Title of Individual [Axis] Title of Individual [Axis] Unrealized loss position, 12 months or greater Unrealized losses, 12 months or greater Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss Warrant liability Warrant [Member] Investment expenses Investment Income, Investment Expense Debt instrument face amount Debt Instrument, Face Amount Remaining deferred issuance costs, net of accumulated amortization Debt Issuance Costs, Line of Credit Arrangements, Net Significant Other Observable Inputs (Level 2) Fair Value, Inputs, Level 2 [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 Warrant liability Warrant Liability Warrant Liability Prior years Liability for Unpaid Claims and Claims Adjustment Expense, Claims Paid, Prior Years Document Quarterly Report Document Quarterly Report After March 1, 2025 After March 1, 2025 [Member] After March 1, 2025 NMIC NMIC [Member] NMIC Equity [Abstract] Total assets Assets, Fair Value Disclosure Earnings per Share, Diluted [Abstract] Net Income (Loss) Available to Common Stockholders, Operations, Diluted [Abstract] 2017 ILN transaction Two Thousand Seventeen ILN Transaction [Member] Two Thousand Seventeen ILN Transaction [Member] Percent of aggregate balance redeemable with equity offerings Debt Instrument, Redemption Price, Percentage Of Principal Amount, Redeemable Debt Instrument, Redemption Price, Percentage Of Principal Amount, Redeemable Subsequent Event [Line Items] Subsequent Event [Line Items] Credit Facility [Domain] Credit Facility [Domain] Earnings per Share, Basic [Abstract] Net Income (Loss) Available to Common Stockholders, Operations, Basic [Abstract] 2018 ILN transaction Two Thousand Eighteen ILN Transaction [Member] Two Thousand Eighteen ILN Transaction [Member] Due after one through five years Debt Securities, Available-for-sale, Maturity, Allocated and Single Maturity Date, Rolling after One Through Five Years, Fair Value Diluted (in shares) Dilutive weighted average shares outstanding (in shares) Weighted Average Number of Shares Outstanding, Diluted Schedule of fair value measurements of financial instruments Fair Value Measurements, Recurring and Nonrecurring [Table Text Block] Basic (in dollars per share) Basic earnings per share (in dollars per share) Earnings Per Share, Basic Change in unrealized investment gains/losses, tax expense OCI, Debt Securities, Available-for-Sale, Gain (Loss), after Adjustment, Tax Entity File Number Entity File Number Debt Disclosure [Abstract] Debt Disclosure [Abstract] Tax and loss bonds Tax And Loss Bond Tax And Loss Bond Amortization of debt discount and debt issuance costs Amortization of Debt Issuance Costs and Discounts Common stock - class A shares, $0.01 par value; 84,808,516 and 68,358,074 shares issued and outstanding as of September 30, 2020 and December 31, 2019, respectively (250,000,000 shares authorized) Common Stock, Value, Outstanding Investment Income, Net [Abstract] Investment Income, Net [Abstract] Net cash provided by (used in) financing activities Net Cash Provided by (Used in) Financing Activities 2017 ILN Transaction 2017 ILN [Member] 2017 ILN [Member] Net premiums written Premiums Written, Net [Abstract] Counterparty Name [Axis] Counterparty Name [Axis] Document Fiscal Year Focus Document Fiscal Year Focus Ceded Ceded Premiums Written Reinsurance recoverable Increase (Decrease) in Reinsurance Recoverable Oaktown Re IV Ltd. Oaktown Re IV Ltd. [Member] Oaktown Re IV Ltd. 2020-1 ILN Transaction 2020-1 ILN [Member] 2020-1 ILN Entity Current Reporting Status Entity Current Reporting Status 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 Investment income Investment Income, Interest and Dividend Total bonds Bonds [Member] 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 Percentage of ceding commission received Ceded Credit Risk, Commission Earned, Percentage Ceded Credit Risk, Commission Earned, Percentage Intangible assets and goodwill Intangible Assets, Net (Including Goodwill) Subsequent Event [Table] Subsequent Event [Table] Purchase of fixed-maturity investments, available-for-sale Payments to Acquire Debt Securities, Available-for-sale Earnings Per Share Earnings Per 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Risk-In-Force Recaptured Debt Instrument [Line Items] Debt Instrument [Line Items] Total shareholders' equity Beginning balance Ending balance Stockholders' Equity Attributable to Parent QSR transactions QSR Transactions [Member] QSR Transactions [Member] Total liabilities and shareholders' equity Liabilities and Equity Commitment fees in interest expense Line of Credit Facility, Commitment Fee Amount Accumulated other comprehensive income, net of tax Accumulated Other Comprehensive Income (Loss), Net of Tax Income Taxes Income Tax Disclosure [Text Block] Entity Address, City or Town Entity Address, City or Town Fair Value Hierarchy and NAV [Axis] Fair Value Hierarchy and NAV [Axis] Financial Instrument [Axis] Financial Instrument [Axis] Anti-dilutive shares (in shares) Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount Ceded risk-in-force Risk In Force, Ceded Risk In Force, Ceded Equity Component [Domain] Equity Component [Domain] Cash and investments held with various state insurance departments Cash, Cash Equivalents, and Short-term Investments Change in unrealized investment gains/losses, net of tax benefit/expense OCI, Debt Securities, Available-for-Sale, Gain (Loss), after Adjustment and Tax Liabilities Liabilities [Abstract] Schedule of Available-for-sale Securities [Table] Schedule of Available-for-sale Securities [Table] Software and equipment, net Property, Plant and Equipment, Net Ceded Credit Risk [Table] Ceded Credit Risk [Table] Entity Tax Identification Number Entity Tax Identification Number Warrant liability, expected life Warrants and Rights Outstanding, Term Net income Net income Net income Net Income (Loss) Attributable to Parent 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 Reclassification adjustment for realized losses (gains) included in net income, tax expense (benefit) Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI for Sale of Securities, Tax Long-term Debt, Type [Axis] Long-term Debt, Type [Axis] Current Fiscal Year End Date Current Fiscal Year End Date Schedule of statutory net income (loss), surplus, contingency reserve and risk-to-capital ratio Statutory Accounting Practices Disclosure [Table Text Block] Effects of Reinsurance [Table] Effects of Reinsurance [Table] Earnings Per Share [Abstract] Earnings Per Share [Abstract] Schedule of investments by industry group Investments Classified By Issuer Industry Group [Table Text Block] Investments Classified By Issuer Industry Group [Table Text Block] Direct Direct Premiums Written Default percent (in percent) Liability For Unpaid Claims And Claims Adjustment Expense, Incurred But Not Reported (IBNR) Claims, Number Of Primary Loans In Default, Percent Of Total Policies In-Force Liability For Unpaid Claims And Claims Adjustment Expense, Incurred But Not Reported (IBNR) Claims, Number Of Primary Loans In Default, Percent Of Total Policies In-Force Shareholders' equity Stockholders' Equity Attributable to Parent [Abstract] Warrants issued (in shares) Class of Warrant or Right, Number of Securities Called by Warrants or Rights Proceeds from maturity of short-term investments Proceeds from Sale of Short-term Investments Document Fiscal Period Focus Document Fiscal Period Focus 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 Statutory net (loss) gain Statutory Accounting Practices, Statutory Net Income Amount Supplemental disclosures of cash flow information Supplemental Cash Flow Information [Abstract] Redemption price (in percent) Debt Instrument, Redemption Price, Percentage Entity Filer Category Entity Filer Category Common Stock - Class A Common stock Common Stock [Member] Ceded Credit Risk, Reinsurer [Domain] Ceded Credit Risk, Reinsurer [Domain] Number of quota share agreements Numer of Quota Share Agreements Numer of Quota Share Agreements Amount retained Reinsurance Retention Policy, Amount Retained 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 Common stock: class A shares issued related to public offering (in shares) Stock Issued During Period, Shares, New Issues Communications Communications, Industry Group [Member] Communications, Industry Group [Member] Due after five through ten years Debt Securities, Available-for-sale, Maturity, Allocated and Single Maturity Date, Rolling after Five Through Ten Years, Fair Value Stated interest rate (in percent) Debt Instrument, Interest Rate, Stated Percentage Unrealized losses, less than 12 months Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Table] Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Table] Common stock: class A shares issued related to warrant exercises (in shares) Stock issued upon exercise of warrants (in shares) Stock Issued During Period, Shares, Conversion of Convertible Securities Percent of premiums ceded under QSR Transaction Percent of pool RIF reinsured Reinsurance Retention Policy, Reinsured Risk, Percentage Applicable premium Debt Instrument, Covenant Terms, Applicable Premium Debt Instrument, Covenant Terms, Applicable Premium Net increase in cash, cash equivalents and restricted cash Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents, Period Increase (Decrease), Including Exchange Rate Effect Basis of Presentation Basis of Accounting, Policy [Policy Text Block] Reinsurance Policy [Domain] Reinsurance Policy [Domain] Basic (in shares) Basic weighted average shares outstanding (in shares) Weighted Average Number of Shares Outstanding, Basic Basis spread on variable rate (in percent) Debt Instrument, Basis Spread on Variable Rate Unearned premiums Increase (Decrease) in Unearned Premiums Expenses Costs and Expenses [Abstract] Subsequent Events [Abstract] Number of securities, total Debt Securities, Available-for-sale, Unrealized Loss Position, Number of Positions Variable Interest Entities Consolidation, Variable Interest Entity, Policy [Policy Text Block] Sale of Stock [Domain] Sale of Stock [Domain] OTTI loss in earnings Other than Temporary Impairment Losses, Investments Direct Direct Premiums Earned Fannie Mae Fannie Mae [Member] Fannie Mae [Member] Interest paid Interest Paid, Excluding Capitalized Interest, Operating Activities Additional paid-in capital Additional Paid in Capital Fair value of long term debt Long-term Debt, Fair Value Total revenues Revenues Current year Current Year Claims and Claims Adjustment Expense Income tax expense Income Tax Expense (Benefit) Income taxes refunded Income Taxes Paid, Net Cash and cash equivalents (including restricted cash of $5,555 and $2,662 as of September 30, 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, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents Debt Securities, Available-for-sale [Table] Debt Securities, Available-for-sale [Table] Title of Individual [Domain] Title of Individual [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] 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 Debt Securities By Industry [Domain] Debt Securities By Industry [Domain] [Domain] for Debt Securities By Industry [Axis] Schedule of Stock by Class [Table] Schedule of Stock by Class [Table] Current Reinsurance Coverage Current Reinsurance Coverage Current Reinsurance Coverage Warrant liability, measurement input Warrants and Rights Outstanding, Measurement Input Roll-forward of Level 3 liabilities: 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 Due after ten years Debt Securities, Available-for-sale, Maturity, Allocated and Single Maturity Date, Rolling after 10 Years, Amortized Cost Entity Emerging Growth Company Entity Emerging Growth Company Accrued investment income Accrued Investment Income Receivable Credit facility borrowing capacity Line of Credit Facility, Maximum Borrowing Capacity Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items] Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items] Repayments of term loan Repayments of term loan Repayments of Secured Debt Maximum Maximum [Member] Reinsurance balances, net Increase (Decrease) in Reinsurance Assets and Liabilities Increase (Decrease) in Reinsurance Assets and Liabilities Net realized investment (losses) 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 Retained Earnings [Member] Claims and claim expenses incurred: Liability for Unpaid Claims and Claims Adjustment Expense, Incurred Claims [Abstract] Effective income tax rate on pre-tax income or loss 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] Net cash (used in) investing activities Net Cash Provided by (Used in) Investing Activities Warrant liability, at fair value Warrants and Rights Outstanding 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] 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] Earnings per Share (EPS) Earnings Per Share [Text Block] Organization, Consolidation and Presentation of Financial Statements [Abstract] Organization, Consolidation and Presentation of Financial Statements [Abstract] Reconciliation of liability for insurance claims and claim expenses Schedule of Liability for Unpaid Claims and Claims Adjustment Expense [Table Text Block] 2019 ILN Transaction 2019 ILN [Member] 2019 ILN [Member] Entity Shell Company Entity Shell Company Key Inputs and Assumptions, Valuation Techniques 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 Schedule of aging unrealized losses Schedule of Unrealized Loss on Investments [Table Text Block] Recent Accounting Pronouncements New Accounting Pronouncements, Policy [Policy Text Block] Statement of Financial Position [Abstract] Statement of Financial Position [Abstract] Statutory Accounting Practices [Line Items] Statutory Accounting Practices [Line Items]