Granted (in shares) Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period Estimated annual effective tax rate Effective Income Tax Rate Reconciliation, Estimated Annual Effective Tax Rate Effective Income Tax Rate Reconciliation, Estimated Annual Effective Tax Rate Document Type Document Type Other comprehensive income (loss): Comprehensive Income (Loss), Net of Tax, Attributable to Parent [Abstract] Stockholders’ Equity Common Stock, Number of Shares, Par Value and Other Disclosures [Abstract] Commitments and Contingencies Commitments and Contingencies Disclosure [Text Block] Schedule of VIE assets and maximum exposure Schedule of Variable Interest Entities [Table Text Block] Related Party [Axis] Related Party [Axis] Treasury Stock Treasury Stock [Member] Reserve for losses and LAE Reserve for losses and LAE at beginning of period Reserve for losses and LAE at end of period Liability for Claims and Claims Adjustment Expense Equity-Based Arrangements, Individual Contracts, Type of Deferred Compensation [Domain] Equity-Based Arrangements, Individual Contracts, Type of Deferred Compensation [Domain] ILN 2015 & 2016 Radnor Re 2019-2 Ltd. [Member] Radnor Re 2019-2 Ltd. [Member] Maximum Exposure to Loss, Off - Balance Sheet Variable Interest Entity, Reporting Entity Involvement, Maximum Loss Exposure, Amount Off The Balance Sheet Variable Interest Entity, Reporting Entity Involvement, Maximum Loss Exposure, Amount Off The Balance Sheet Investments Investments in Debt and Marketable Equity Securities (and Certain Trading Assets) Disclosure [Text Block] Reserve rate Risk In Force, Reserve Percentage Risk In Force, Reserve Percentage Statutory Accounting Practices [Table] Statutory Accounting Practices [Table] Rollforward of accumulated other comprehensive income (loss) Schedule of Accumulated Other Comprehensive Income (Loss) [Table Text Block] Vested (in dollars per share) Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Vested in Period, Weighted Average Grant Date Fair Value Significant Unobservable Inputs (Level 3) Fair Value, Inputs, Level 3 [Member] Accrued expenses Deferred Tax Liabilities Tax Deferred Expense Reserves and Accruals Accrued Liabilities Amount of deferred tax liability attributable to taxable temporary differences from accrued liabilities. Unamortized deferred costs Debt Issuance Costs, Gross Effect of reinsurance Effects of Reinsurance [Table Text Block] Fixed maturities available for sale, at fair value (amortized cost: 2020 — $3,393,601; 2019 — $2,967,225) Fixed maturities Fixed Maturities [Member] Statistical Measurement [Domain] Statistical Measurement [Domain] Liabilities and Stockholders’ Equity Liabilities and Equity [Abstract] Net premiums earned: Premiums Earned, Net [Abstract] Stock-based compensation Share-based Compensation Arrangement by Share-based Payment Award [Line Items] Other comprehensive income (loss): Other Comprehensive Income (Loss), Tax, Portion Attributable to Parent, Parenthetical Disclosures [Abstract] Net deferred tax liability Deferred Income Tax Liabilities, Net Fair Value Debt Securities Available For Sale Continuous Unrealized Loss Position [Abstract] Debt Securities Available For Sale Continuous Unrealized Loss Position [Abstract] Security Exchange Name Security Exchange Name Payment of issuance costs for credit facility Payments of Debt Issuance Costs Cancellation of treasury stock Treasury Stock, Retired, Cost Method, Amount Reinsurance Disclosures [Abstract] Reinsurance Disclosures [Abstract] Performance Shares Performance Shares [Member] Outstanding at beginning of year (in dollars per share) Outstanding at end of period (in dollars per share) Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value Investments by Consolidated and Nonconsolidated Entities [Axis] Investments by Consolidated and Nonconsolidated Entities [Axis] Mortgage Insurance Linked Notes Mortgage Insurance Linked Notes [Member] Mortgage Insurance Linked Notes [Member] Realized gross losses Debt Securities, Available-for-sale, Realized Loss Commitments and contingencies (see Note 7) Commitments and Contingencies Second Vesting Period Share-based Payment Arrangement, Tranche Two [Member] Treasury stock acquired Payments for Repurchase of Common Stock Assets Assets [Abstract] Award vesting period Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Period Accounting Policies [Abstract] Accounting Policies [Abstract] Due after 5 but within 10 years Debt Securities, Available-for-sale, Maturity, Allocated and Single Maturity Date, Rolling after Five Through Ten Years, Amortized Cost Vested (in shares) Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Vested in Period Other Information Other Information [Abstract] Other Information [Abstract] Sublease income Sublease Income Accumulated Other Comprehensive Income (Loss) Comprehensive Income (Loss) Note [Text Block] Consumer, non-cyclical Consumer, Non-cyclical Sector [Member] Consumer, Non-cyclical Sector [Member] Maximum Exposure to Loss, On - Balance Sheet Variable Interest Entity, Reporting Entity Involvement, Maximum Loss Exposure, Amount On The Balance Sheet Variable Interest Entity, Reporting Entity Involvement, Maximum Loss Exposure, Amount On The Balance Sheet Estimated fair values and carrying amounts of financial instruments Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] Retained earnings Retained Earnings (Accumulated Deficit) Operating lease Operating Lease, Right-of-Use Asset Entity Address, Country Entity Address, Country Other underwriting and operating expenses Other Underwriting and Operating Expenses Represents the aggregate amount of costs incurred during the period, such as those relating to general administration and policy maintenance that do not vary with, and are not primarily related to the acquisition or renewal of insurance contracts and other operating costs, that are associated with the entity's normal revenue producing operation. 2021 Lessee, Operating Lease, Liability, to be Paid, Year One Incentive Program Bonus Award Fiscal Year Performance Incentive Program Bonus Award Fiscal Year Performance [Member] Represents an incentive program covering bonus awards based on performance for previous fiscal year. Income tax payments Income Taxes Paid AOCI tax effect, beginning of period AOCI tax effect, end of period AOCI Tax, Attributable to Parent 2024 Lessee, Operating Lease, Liability, to be Paid, Year Four Schedule of assets and liabilities measured at fair vale on a recurring basis Schedule of Fair Value, Assets and Liabilities Measured on Recurring Basis [Table Text Block] Deferred policy acquisition costs Increase (Decrease) in Deferred Policy Acquisition Costs AOCI before tax, beginning of period AOCI before tax, end of period AOCI before Tax, Attributable to Parent Net of Tax AOCI Attributable to Parent, Net of Tax [Roll Forward] Credit Concentration Risk Credit Concentration Risk [Member] Lease cost Total lease cost Lease, Cost Purchase of other invested assets Payments to Acquire Equity Method Investments Common shares, par value (in dollars per share) Common Stock, Par or Stated Value Per Share Special tax bonds Special Tax Bonds [Member] Special Tax Bonds Investment Secondary Categorization [Axis] Investment Secondary Categorization [Axis] Other comprehensive income (loss): Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Parent [Abstract] Unearned premium reserve Unearned Premiums Compounded Annual Book Value Per Share Growth 13% Compounded Annual Book Value Per Share Growth Achieved 13 Percent [Member] Represents information pertaining to 13% compounded annual book value per share growth achieved. Stock-based compensation expense APIC, Share-based Payment Arrangement, Increase for Cost Recognition Measurement Frequency [Domain] Measurement Frequency [Domain] Nonvested Shares, Share Units Nonvested Shares, Share Units [Member] Nonvested Shares, Share Units [Member] Third Vesting Period Share-based Payment Arrangement, Tranche Three [Member] Dividends Payable [Line Items] Dividends Payable [Line Items] Concentration risk, percentage Concentration Risk, Percentage EPS calculation Earnings Per Share, Diluted, by Common Class, Including Two Class Method [Line Items] Accumulated Other Comprehensive Income (Loss), Net of Tax [Abstract] Accumulated Other Comprehensive Income (Loss), Net of Tax [Abstract] Accrued investment income Increase (Decrease) in Accrued Investment Income Receivable Statement Statement [Line Items] Organizational expenditures Deferred Tax Assets, Organizational Expenses Represents the amount before the allocation of valuation allowances of deferred tax asset attributable to deductible temporary differences from organizational expenditures. Increase in contingency reserve Statutory Accounting Practices, Increase (Decrease) in Contingency Reserve Represents the amount of increase (decrease) in contingency reserve. Forecast Forecast [Member] Essent Guaranty Essent Guaranty Inc [Member] Represents information pertaining to Essent Guaranty, Inc. (Essent Guaranty), a regulated and licensed indirect wholly-owned subsidiary of the reporting entity. Earnings per share: Earnings Per Share, Basic and Diluted [Abstract] Credit facility borrowings Proceeds from Long-term Lines of Credit Collaborative Arrangement and Arrangement Other than Collaborative [Table] Collaborative Arrangement and Arrangement Other than Collaborative [Table] Statement [Table] Statement [Table] Basic materials Basic Materials Sector [Member] Basic Materials Sector [Member] Statistical Measurement [Axis] Statistical Measurement [Axis] Reinsurance Reinsurance [Text Block] Credit Facility [Axis] Credit Facility [Axis] Net change in short-term investments Payments for (Proceeds from) Short-term Investments U.S. agency securities US Government Agencies Debt Securities [Member] Reinsurance retention policy, debt issued to cover insurance, term Reinsurance, Debt Issued To Cover Insurance, Term Reinsurance, Debt Issued To Cover Insurance, Term Net reserve for losses and LAE at beginning of period Net reserve for losses and LAE at end of period Liability for Unpaid Claims and Claims Adjustment Expense, Net Entity Small Business Entity Small Business Changes in Stockholders' Equity Increase (Decrease) in Stockholders' Equity [Roll Forward] Number of shares issued in transaction Sale of Stock, Number of Shares Issued in Transaction Fair Value Hierarchy and NAV [Domain] Fair Value Hierarchy and NAV [Domain] Debt Obligations Debt Disclosure [Text Block] Issuance of common shares, net of costs Proceeds from Issuance of Common Stock Excess tax benefits from stock-based compensation Effective Income Tax Rate Reconciliation, Tax Expense (Benefit), Share-based Payment Arrangement, Percent Amendment Flag Amendment Flag Schedule of reconciliation of net income and weighted average common shares outstanding used in computations of basic and diluted earnings per common share Schedule of Earnings Per Share, Basic and Diluted [Table Text Block] Disclosure of share-based compensation arrangements by share-based payment award Disclosure of Share-based Compensation Arrangements by Share-based Payment Award [Table Text Block] Weighted average shares outstanding: Weighted Average Number of Shares Outstanding, Diluted [Abstract] Amount paid for remedies (less than) Loss Contingency Accrual, Payments Credit facility borrowings (at carrying value, less unamortized deferred costs of $342 in 2020 and $763 in 2019) Outstanding amount Long-term Line of Credit Loss reserves - TCJA transition adjustment Deferred Tax Liability Tax Cuts And Jobs Act Deferred Tax Liability Tax Cuts And Jobs Act Less: Reclassification adjustment for gains included in net income, net of tax Reclassification from AOCI, Current Period, Net of Tax, Attributable to Parent Increase of margin component of reinsurance premium Risk Margin Increase After Optional Termination Date Risk Margin Increase After Optional Termination Date Net cash provided by operating activities Net Cash Provided by (Used in) Operating Activities Prior years Favorable prior year development Prior Year Claims and Claims Adjustment Expense Entity Central Index Key Entity Central Index Key Related Party [Domain] Related Party [Domain] Measurement Frequency [Axis] Measurement Frequency [Axis] Financial Instruments [Domain] Financial Instruments [Domain] Statutory capital and surplus Statutory Accounting Practices, Statutory Capital and Surplus, Balance Tax exempt interest, net of proration Income Tax Reconciliation at Weighted Average Income Tax Rate Tax Exempt Income Amount of the difference between reported income tax expense (benefit) and expected income tax expense (benefit) computed by applying the weighted average income tax rate to pretax income (loss) from continuing operations attributable to income (loss) exempt from income taxes. Certain members of senior management Certain Senior Management [Member] Represents some, but not all, of a team of individuals at the highest level of organizational management who have the day-to-day responsibilities of managing the entity. Liability for Future Policy Benefits and Unpaid Claims and Claims Adjustment Expense [Abstract] Liability for Future Policy Benefits and Unpaid Claims and Claims Adjustment Expense [Abstract] 12 months or more Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer Total losses and expenses Benefits, Losses and Expenses Tax Effect AOCI Attributable To Parent, Tax [Roll Forward] AOCI Attributable To Parent, Tax Less: Reclassification adjustment for gains included in net income, tax effect Reclassification from AOCI, Current Period, Tax Change in fair market value of derivatives Deferred Tax Assets, Derivative Instruments Amortized cost Amortized Cost Amortized Cost Debt Securities, Available-for-sale, Amortized Cost Renewal term (up to) Lessee, Operating Lease, Renewal Term Unrealized Gains Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax Compounded Annual Book Value Per Share Growth 14% Compounded Annual Book Value Per Share Growth Achieved 14 Percent [Member] Represents information pertaining to 14% compounded annual book value per share growth achieved. Statement of Cash Flows [Abstract] Statement of Cash Flows [Abstract] Remaining Insurance in Force Reinsurance, Remaining Insurance In Force Reinsurance, Remaining Insurance In Force Summary of nonvested Common Share and nonvested Common Share unit activity Share-based Payment Arrangement, Restricted Stock and Restricted Stock Unit, Activity [Table Text Block] Other accrued liabilities Other Accrued Liabilities Compounded Annual Book Value Per Share Growth 15% Compounded Annual Book Value Per Share Growth Achieved 15 Percent [Member] Represents information pertaining to 15% compounded annual book value per share growth achieved. Entity Common Stock, Shares Outstanding Entity Common Stock, Shares Outstanding 2022 Lessee, Operating Lease, Liability, to be Paid, Year Two Schedule of net investment income Investment Income [Table Text Block] Dividends Payable [Table] Dividends Payable [Table] Mortgage Insurance Mortgage Insurance [Member] Mortgage Insurance [Member] Schedule of investments available for sale Schedule of Available-for-sale Securities Reconciliation [Table Text Block] Ceded premiums earned related to percent of risk on all other eligible policies written Reinsurance, Ceded Premiums Earned, Percent Of Risk On All Other Eligible Policies Reinsurance, Ceded Premiums Earned, Percent Of Risk On All Other Eligible Policies Schedule of lease cost and other information Lease, Cost [Table Text Block] Credit Facility [Table] Line of Credit Facility [Table] Loans in default at end of period Number of Loans in Default Represents the number of loans in default. Schedule of Earnings Per Share, Diluted, by Common Class, Including Two Class Method [Table] Schedule of Earnings Per Share, Diluted, by Common Class, Including Two Class Method [Table] 2023 Lessee, Operating Lease, Liability, to be Paid, Year Three Plan Name [Axis] Plan Name [Axis] Reserve for losses and LAE Increase (Decrease) in Liability for Claims and Claims Adjustment Expense Reserve Issuance of common shares, net of issuance costs Stock Issued During Period, Value, New Issues Residential mortgage down payment percentage for which mortgage insurance is generally required (less than) Financing Receivable Consumer Mortgage Insured Down Payment Percentage Represents the percentage of the total sale price that a home buyer contributes in cash towards the purchase of a home for which mortgage insurance is generally required. Total assets Total VIE Assets Assets Scenario [Axis] Scenario [Axis] Non-U.S. government securities Non-U.S. government securities: Debt Security, Government, Non-US [Member] Unrealized (gain) loss on investments Deferred Tax Liabilities, Unrealized Gains on Trading Securities Recently Issued Accounting Standards Organization, Consolidation, Basis of Presentation, Business Description and Accounting Policies [Text Block] Outstanding at beginning of year (in shares) Outstanding at end of period (in shares) Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number Title of 12(b) Security Title of 12(b) Security Reserve for Losses and Loss Adjustment Expenses Liability for Future Policy Benefits and Unpaid Claims Disclosure [Text Block] Investments in limited partnerships Deferred Tax Liabilities, Investments 2025 and thereafter Lessee, Operating Lease, Liability, to be Paid, after Year Four Lessee, Operating Lease, Liability, to be Paid, after Year Four Other-than-temporary impairments Other-than-temporary Impairment Loss, Debt Securities, Available-for-sale, Recognized in Earnings Subsequent Event Type [Axis] Subsequent Event Type [Axis] Investments, Debt and Equity Securities [Abstract] Investments, Debt and Equity Securities [Abstract] Vesting [Domain] Vesting [Domain] Interest expense Interest Expense Consideration received on transaction Sale of Stock, Consideration Received on Transaction Depreciation and amortization Depreciation, Depletion and Amortization Short-term investments available for sale, at fair value (amortized cost: 2020 — $952,952; 2019 — $315,360) Short-term investments Short-term Investments [Member] Schedule of components of income tax expense Schedule of Components of Income Tax Expense (Benefit) [Table Text Block] Gross Unrealized Losses Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss [Abstract] Total liabilities Liabilities Investment Type [Axis] Investment Type [Axis] Insurance [Abstract] Insurance [Abstract] Other Income Tax Reconciliation at Weighted Average Income Tax Rate Other Adjustments Amount of the difference between reported income tax expense (benefit) and expected income tax expense (benefit) computed by applying the weighted average income tax rate to pretax income (loss) from continuing operations attributable to other adjustments. Internal Credit Assessment [Domain] Internal Credit Assessment [Domain] Expected weighted average period for recognition of expense Share-based Payment Arrangement, Nonvested Award, Cost Not yet Recognized, Period for Recognition Less: Future interest expense Lessee, Operating Lease, Liability, Undiscounted Excess Amount Total Debt Securities, Available-for-sale, Unrealized Loss Position Banking Regulation, Total Capital [Abstract] Banking Regulation, Total Capital [Abstract] Radnor Re 2020-2 Radnor Re 2020-2 [Member] Radnor Re 2020-2 2020 Performance-Based Grants Two Thousand Twenty Performance-Based Grants [Member] Two Thousand Twenty Performance-Based Grants [Member] Commitments and Contingencies Disclosure [Abstract] Commitments and Contingencies Disclosure [Abstract] Maximum Exposure to Loss Variable Interest Entity, Reporting Entity Involvement, Maximum Loss (Gain) Exposure, Amount Variable Interest Entity, Reporting Entity Involvement, Maximum Loss (Gain) Exposure, Amount Net income Net income Net Income (Loss) Available to Common Stockholders, Basic Quoted Prices in Active  Markets for Identical Instruments (Level 1) Fair Value, Inputs, Level 1 [Member] Weighted average interest during period Debt, Weighted Average Interest Rate Amortized Cost Debt Securities, Available-for-sale, Maturity, Fair Value, Rolling Maturity [Abstract] Number of states in which the entity is licensed to write mortgage insurance Number of States in which Entity Operates Less than 12 months Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months Number of Shares Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward] Essent Re Essent Reinsurance Ltd [Member] Represents information pertaining to Essent Reinsurance Ltd. (Essent Re), a wholly-owned Bermuda-domiciled Class 3A Insurer licensed pursuant to Section 4 of the Bermuda Insurance Act 1978, which offers mortgage-related insurance and reinsurance. Quarterly cash dividends paid (in dollars per share) Common Stock, Dividends, Per Share, Cash Paid Realized gross gains Debt Securities, Available-for-sale, Realized Gain Maximum percent of individual ownership Shareholder Voting Rights Ownership Percentage Threshold Shareholder Voting Rights Ownership Percentage Threshold Debt Instrument [Axis] Debt Instrument [Axis] Additional Paid-In Capital Additional Paid-in Capital [Member] Financial Assets: Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract] Other assets Other Assets Other accrued liabilities Increase (Decrease) in Accrued Liabilities Treasury stock acquired Treasury Stock, Value, Acquired, Cost Method Start-up expenditures, net Deferred Tax Assets, Start Up Expenses Net Represents the amount before allocation of valuation allowances of deferred tax asset attributable to deductible temporary differences from net start-up expenditures. 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] Change in unrealized appreciation of investments, net of tax expense of $3,856 and $3,640 in the three months ended September 30, 2020 and 2019 and $14,469 and $18,685 in the nine months ended September 30, 2020 and 2019 Other Comprehensive Income (Loss), Available-for-sale Securities Adjustment, Net of Tax, Portion Attributable to Parent Internal Credit Assessment [Axis] Internal Credit Assessment [Axis] Common shares, outstanding (in shares) Common Stock, Shares, Outstanding Other invested assets Equity Method Investments Net deferred tax asset Deferred Tax Assets, Net [Abstract] Income Tax Disclosure [Abstract] Income Tax Disclosure [Abstract] Net loss and LAE payments during the current period Liability for Unpaid Claims and Claims Adjustment Expense, Claims Paid Contingency reserve liability Statutory Accounting Practices, Statutory Contingency Reserve Liability Represents the amount of contingency reserve liability, as of the balance sheet date, using prescribed or permitted statutory accounting practices (rather than GAAP, if different) of the state or country. Revolving Credit Facility Revolving Credit Facility [Member] Radnor Re 2018-1 Ltd. ILN 2017 Radnor Re 2018-1 Ltd. [Member] Radnor Re 2018-1 Ltd. Loss Contingency Nature [Axis] Loss Contingency Nature [Axis] Variable Interest Entity, Not Primary Beneficiary Variable Interest Entity, Not Primary Beneficiary [Member] Due after 10 years Debt Securities, Available-for-sale, Maturity, Allocated and Single Maturity Date, Rolling after 10 Years, Fair Value Subsequent Event Subsequent Event [Member] Common shares, authorized (in shares) Common Stock, Shares Authorized Unearned ceding commissions Deferred Tax Assets, Deferred Expense, Unearned Ceding Commissions Deferred Tax Assets, Deferred Expense, Unearned Ceding Commissions Concentration Risk Type [Axis] Concentration Risk Type [Axis] Schedule of realized gross gains and losses on sale of investments available for sale Schedule of Realized Gain (Loss) [Table Text Block] Statutory surplus Statutory Accounting Practices, Statutory Surplus Balance Represents the amount of statutory surplus (stockholders' equity), as of the balance sheet date, using prescribed or permitted statutory accounting practices (rather than GAAP, if different) of the state or country. Due in 1 year Debt Securities, Available-for-sale, Maturity, Allocated and Single Maturity Date, Rolling within One Year, Amortized Cost Insurance Premium Revenue Recognition Collaborative Arrangement and Arrangement Other than Collaborative [Line Items] Accumulated Other Comprehensive Income (Loss) AOCI Attributable to Parent [Member] Schedule of amortized cost and fair value of investments available for sale by contractual maturity Investments Classified by Contractual Maturity Date [Table Text Block] Tax provision at weighted average statutory rates Effective Income Tax Rate Reconciliation at Weighted Average Statutory Income Tax Rate Percentage of weighted average statutory tax rate applicable to pretax income (loss). Vesting Criteria [Domain] Vesting Criteria [Domain] The types of vesting specified for share-based compensation awards. Provision for losses and LAE Net incurred losses and LAE during the current period Liability for Unpaid Claims and Claims Adjustment Expense, Incurred Claims Unassigned surplus Dividend Payments Restrictions Schedule, Statutory Capital and Surplus Vesting Criteria [Axis] Vesting Criteria [Axis] Information about the type of vesting for share-based compensation awards. SEC Schedule, 12-17, Insurance Companies, Reinsurance [Line Items] SEC Schedule, 12-17, Insurance Companies, Reinsurance [Line Items] Radnor Re Radnor Re [Member] Radnor Re [Member] Investing Activities Net Cash Provided by (Used in) Investing Activities, Continuing Operations [Abstract] Excess tax benefits from stock-based compensation Effective Income Tax Rate Reconciliation, Tax Expense (Benefit), Share-based Payment Arrangement, Amount Dividends and dividend equivalents declared Dividends Other Reinsurance Other Reinsurance [Member] Other Reinsurance [Member] Comprehensive income Comprehensive Income (Loss), Net of Tax, Attributable to Parent Schedule of reconciliation of difference between income tax expense and expected tax provision at weighted average tax rate Schedule of Effective Income Tax Rate Reconciliation [Table Text Block] Realized investment gains, net Gain on the sale of investments, net Realized Investment Gains (Losses) Compounded Annual Book Value Per Share Growth 16% Compounded Annual Book Value Per Share Growth Achieved 16 Percent [Member] Compounded Annual Book Value Per Share Growth Achieved 16 Percent [Member] Performance -Based Vesting Based On Performance [Member] Represents a share based compensation award with vesting based on achievement of performance conditions. Scenario [Domain] Scenario [Domain] Unrealized holding gains arising during the period, net of tax OCI, before Reclassifications, Net of Tax, Attributable to Parent Counterparty Name [Domain] Counterparty Name [Domain] Legal Entity [Axis] Legal Entity [Axis] Purchase of property and equipment Payments to Acquire Property, Plant, and Equipment City Area Code City Area Code Percentage of debt securities Investment Owned, Percent of Net Assets Document Period End Date Document Period End Date Effect of percentage point decrease on liability claim and claim expense adjustment expense Liability For Claims And Claims Adjustment Expense, Effect Of Percentage Point Decrease on Liability Claim And Claim Expense Adjustment Expense Liability For Claims And Claims Adjustment Expense, Effect Of Percentage Point Decrease on Liability Claim And Claim Expense Adjustment Expense Total Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss Director Director [Member] Equity in net loss (income) of other invested assets Income (Loss) from Equity Method Investments Income before income taxes Income (Loss) from Continuing Operations before Equity Method Investments, Income Taxes, Noncontrolling Interest Non-deductible expenses Effective Income Tax Rate Reconciliation Weighted Average Statutory Income Tax Rate Non-deductible Expense Percentage of the difference between reported income tax expense (benefit) and expected income tax expense (benefit) computed by applying the weighted average statutory income tax rate to pretax income (loss) from continuing operations attributable to nondeductible expenses. Unrealized holding gains arising during the period, tax effect Other Comprehensive Income (Loss) before Reclassifications, Tax Schedule of compensation expense, net of forfeitures, and related tax effects recognized in connection with nonvested shares Share-based Payment Arrangement, Cost by Plan [Table Text Block] Stock-based compensation expense Share-based Payment Arrangement, Noncash Expense Entity [Domain] Entity [Domain] Fixed assets Deferred Tax Assets, Property, Plant and Equipment Change in unrealized appreciation (depreciation) of investments, tax expense (benefit) Other Comprehensive Income (Loss), Available-for-sale Securities, Tax, Portion Attributable to Parent Cover [Abstract] Cover [Abstract] Statutory Accounting Practices, Statutory Amount Available for Dividend Payments [Abstract] Statutory Accounting Practices, Statutory Amount Available for Dividend Payments [Abstract] Assets on deposit for the benefit of the sponsor Assets On Deposit For The Benefit Of The Sponsor Assets On Deposit For The Benefit Of The Sponsor ILN Radnor Entities [Member] Radnor Entities [Member] Distribution of income from other invested assets Proceeds from Equity Method Investment, Distribution Property and equipment Property, Plant and Equipment, Net [Abstract] Reinsurance for mortgage insurance coverage in excess of 25% Excess Mortgage Insurance Coverage [Member] Represents an arrangement to assume that portion of the risk retained by an affiliate that is in excess of 25% of the balance of any mortgage loan insured by that affiliate after consideration of other reinsurance agreements at that affiliate, in accordance with certain state law requirements. Number of votes per share Common Stock Number Of Votes Per Share Common Stock Number Of Votes Per Share Affiliated Entity Affiliated Entity [Member] Fair Value Disclosures [Abstract] Fair Value Disclosures [Abstract] Total investments Investments COVID-19 COVID-19 [Member] COVID-19 [Member] Reconciliation of the beginning and ending reserve balances for losses and loss adjustment expenses (LAE) Liability for Unpaid Claims and Claims Adjustment Expense [Roll Forward] Concentration Risk Benchmark [Axis] Concentration Risk Benchmark [Axis] Lease cost: Lease, Cost [Abstract] Total investments available for sale Fair Value Debt Securities, Available-for-sale Equity Components [Axis] Equity Components [Axis] Nonvested shares Restricted Stock [Member] Essent PA Essent Guaranty Of P A Inc [Member] Represents information pertaining to Essent Guaranty of PA, Inc. (Essent PA), a regulated and licensed indirect wholly-owned subsidiary of the reporting entity. Share-based Payment Arrangement [Abstract] Share-based Payment Arrangement [Abstract] Debt Instrument, Name [Domain] Debt Instrument, Name [Domain] Due after 1 but within 5 years Debt Securities, Available-for-sale, Maturity, Allocated and Single Maturity Date, Rolling after One Through Five Years, Amortized Cost Deferred tax assets Deferred Tax Assets, Gross Minimum Minimum [Member] Special revenue bonds Special Revenue Municipal Bonds [Member] A municipal bond whose debt service is payable solely from the revenues derived from operating the facilities acquired or constructed with the proceeds of the bonds. RIF ceded Risk In Force, Ceded Risk In Force, Ceded Net premiums written Net premiums written Premiums Written, Net Total unrecognized compensation expense Share-based Payment Arrangement, Nonvested Award, Excluding Option, Cost Not yet Recognized, Amount 2013 Plan Essent Group Limited2013 Long Term Incentive Plan [Member] Represents the Essent Group Limited 2013 Long-term Incentive Plan (2013 Plan). Prepaid federal income tax Net purchases of T&L Bonds Increase (Decrease) in Mortgage Guaranty Insurer United States Mortgage Guaranty Tax and Loss Bonds Represents, for a mortgage guaranty insurer, the increase (decrease) during the reporting period in the amount of investment in United States Mortgage Guaranty Tax and Loss Bonds issued by the Treasury Department for eligibility for certain tax deductions under enacted tax laws. Ceded Ceded Premiums Earned Remaining Risk in Force Reinsurance, Remaining Risk In Force Reinsurance, Remaining Risk In Force Forfeited (in dollars per share) Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Forfeitures, Weighted Average Grant Date Fair Value 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] Capital Stock Stockholders' Equity Note Disclosure [Text Block] Components of the net deferred tax asset Components of Deferred Tax Assets and Liabilities [Abstract] Schedule of fair value of investments in an unrealized loss position and related unrealized losses Debt Securities, Available-for-sale, Unrealized Loss Position, Fair Value [Table Text Block] Current period Liability for Unpaid Claims and Claims Adjustment Expense, Claims Paid, Current Year Proceeds from maturity of investments available for sale Proceeds from Maturities, Prepayments and Calls of Debt Securities, Available-for-sale Percentage of award issuable if current period end were end of contingency period Share-based Compensation Arrangement by Share-based Payment Award, Award Period to Date Vesting Rights, Percentage Percentage of vesting of share-based compensation awards if the end of the current reporting period were the end of the vesting period. Credit facility, commitment fee rate Line of Credit Facility, Commitment Fee Percentage Ceding commission, percent Reinsurance, Ceded Premiums Earned, Ceding Commission, Percent Reinsurance, Ceded Premiums Earned, Ceding Commission, Percent Increase in maximum borrowing capacity Line of Credit Facility, Maximum Borrowing Capacity, Period Increase Line of Credit Facility, Maximum Borrowing Capacity, Period Increase Unusual or Infrequent Item, or Both [Axis] Unusual or Infrequent Item, or Both [Axis] Additional paid-in capital Additional Paid in Capital, Common Stock Entity Registrant Name Entity Registrant Name Subsequent Event Type [Domain] Subsequent Event Type [Domain] Time-Based Share Awards Time-Based Vesting Based On Service [Member] Represents a share based compensation award with vesting based on length of service. Statement of Stockholders' Equity [Abstract] Statement of Stockholders' Equity [Abstract] Employee Employee [Member] Employee [Member] Weighted average discount rate - operating leases Operating Lease, Weighted Average Discount Rate, Percent Deduct payments for losses and LAE, net of reinsurance, occurring in: Liability for Unpaid Claims and Claims Adjustment Expense, Claims Paid [Abstract] Profit commission, percent, maximum Reinsurance, Profit Commissions, Maximum Reinsurance, Profit Commissions, Maximum Ceded premiums earned related to percent of risk on eligible single premium policies Reinsurance, Ceded Premiums Earned, Percent Of Risk On Eligible Single Premium Policies Reinsurance, Ceded Premiums Earned, Percent Of Risk On Eligible Single Premium Policies Deferred tax liabilities Deferred Tax Liabilities, Gross Reinsurance Policy, Type [Axis] Reinsurance Policy, Type [Axis] Assets on deposit under reinsurance agreement Assets on Deposit Under Reinsurance Agreements Assets on Deposit Under Reinsurance Agreements Communications Communications Sector [Member] Communications Sector [Member] Tax allocation bonds Tax Allocation Municipal Bonds [Member] Bonds issued in conjunction with a redevelopment project. The taxes pledged to their repayment come from the increase of assessed value over and above a pre-established base. The redevelopment creates this added value, known as the tax increment. Components of income tax expense Components of Income Tax Expense (Benefit), Continuing Operations [Abstract] Net investment income Net investment income Net Investment Income Nonvested Shares, Share Units Or DEU Nonvested Shares, Share Units Or DEU [Member] Nonvested Shares, Share Units Or DEU [Member] Dividends paid Payments of Ordinary Dividends, Common Stock Reinsurance for mortgage insurance coverage threshold (in excess of) Reinsurance Retention Policy, Reinsured Risk, Percentage Threshold Threshold percentage of risk reinsured on insurance products per entity policy. Entity Incorporation, State or Country Code Entity Incorporation, State or Country Code Total lease payments to be paid Lessee, Operating Lease, Liability, to be Paid Reserve for losses and LAE, for prior years Liability for Unpaid Claims and Claims Adjustment Expense Prior Years Liability, as of the balance sheet date, for amounts representing estimated cost of settling unpaid claims for prior years under the terms of the underlying insurance policies, less estimated reinsurance recoveries on such claims. This includes an estimate for claims which have been incurred but not reported. Claim adjustment expenses represent the costs estimated to be incurred in the settlement of unpaid claims. Investments by Secondary Categorization [Domain] Investments by Secondary Categorization [Domain] Deferred policy acquisition costs Deferred Policy Acquisition Cost Unrealized Losses Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax Entity Address, Postal Zip Code Entity Address, Postal Zip Code Cash Cash Investments available for sale Debt Securities, Available-for-sale [Line Items] Total other comprehensive income Other comprehensive income Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Parent Document Transition Report Document Transition Report Title of Individual [Axis] Title of Individual [Axis] 12 months or more Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss Non-deductible expenses Income Tax Reconciliation at Weighted Average Income Tax Rate Nondeductible Expense Amount of the difference between reported income tax expense (benefit) and expected income tax expense (benefit) computed by applying the weighted average income tax rate to pretax income (loss) from continuing operations attributable to nondeductible expenses. Essent PA Essent PA [Member] Essent PA [Member] Remaining Reinsurance in Force Reinsurance, Remaining Reinsurance In Force Reinsurance, Remaining Reinsurance In Force Quarterly cash dividends declared (in dollars per share) Common Stock, Dividends, Per Share, Declared Investment expenses Investment Income, Investment Expense Prepaid expenses Deferred Tax Liabilities, Prepaid Expenses Significant Other Observable Inputs (Level 2) Fair Value, Inputs, Level 2 [Member] Prior years Incurred claims and claim adjustment expenses Liability for Unpaid Claims and Claims Adjustment Expense, Claims Paid, Prior Years Document Quarterly Report Document Quarterly Report Vesting [Axis] Vesting [Axis] Total assets at fair value Assets, Fair Value Disclosure Issuance costs Adjustments to Additional Paid in Capital, Stock Issued, Issuance Costs Equity-Based Arrangements, Individual Contracts, Type of Deferred Compensation [Axis] Equity-Based Arrangements, Individual Contracts, Type of Deferred Compensation [Axis] Other comprehensive income, before tax Other Comprehensive Income (Loss), before Tax, Portion Attributable to Parent Compounded Annual Book Value Per Share Growth 17% Compounded Annual Book Value Per Share Growth Achieved 17 Percent [Member] Compounded Annual Book Value Per Share Growth Achieved 17 Percent [Member] Loss reserves Deferred Tax Assets, Tax Deferred Expense, Reserves and Accruals, Loss Reserves Schedule of coverages and retentions Reinsurance Retention Policy [Table Text Block] 2018 Performance-Based Grants Two Thousand Eighteen Performance-Based Grants [Member] Two Thousand Eighteen Performance-Based Grants [Member] Industrial Industrial Sector [Member] Industrial Sector [Member] Less: Reinsurance recoverables Plus: Reinsurance recoverables Reinsurance Recoverable for Unpaid Claims and Claims Adjustments Credit Facility [Domain] Credit Facility [Domain] Due after 1 but within 5 years Debt Securities, Available-for-sale, Maturity, Allocated and Single Maturity Date, Rolling after One Through Five Years, Fair Value Diluted (in shares) Diluted weighted average shares outstanding (in shares) Weighted Average Number of Shares Outstanding, Diluted Basic (in dollars per share) Basic earnings per share (in dollars per share) Earnings Per Share, Basic Securities Securities [Member] Securities [Member] Entity File Number Entity File Number Forfeited (in shares) Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Forfeited in Period Debt Disclosure [Abstract] Debt Disclosure [Abstract] Other Effective Income Tax Rate Reconciliation Weighted Average Statutory Income Tax Rate Other Adjustments Percentage of the difference between reported income tax expense (benefit) and expected income tax expense (benefit) computed by applying the weighted average statutory income tax rate to pretax income (loss) from continuing operations attributable to other adjustments. Weighted average remaining lease term - operating leases Operating Lease, Weighted Average Remaining Lease Term Uncommited Line Uncommitted Line of Credit [Member] Uncommitted Line of Credit Tax provision at weighted average statutory rates Income Tax Reconciliation Income Tax Expense Benefit at Weighted Average Income Tax Rate The amount of income tax expense or benefit for the period computed by applying the weighted average income tax rate to pretax income from continuing operations. Operating Activities Net Cash Provided by (Used in) Operating Activities, Continuing Operations [Abstract] Indemnifications related to contract underwriting services Indemnification Agreement [Member] Net cash provided by (used in) financing activities Net Cash Provided by (Used in) Financing Activities ILN 2019 Radnor Re 2020-1 Ltd. Radnor Re 2020-1 [Member] Radnor Re 2020-1 [Member] Tax exempt interest, net of proration Effective Income Tax Rate Reconciliation Weighted Average Statutory Income Tax Rate Tax Exempt Income Percentage of the difference between reported income tax expense (benefit) and expected income tax expense (benefit) computed by applying the weighted average statutory income tax rate to pretax income (loss) from continuing operations attributable to income (loss) exempt from income taxes. Net premiums written: Premiums Written, Net [Abstract] Compounded Annual Book Value Per Share Growth Compounded Annual Book Value Per Share Growth Rate Represents the compounded annual book value per share growth rate, expressed as a percentage. Contingency reserves Deferred Tax Liabilities Contingency Reserves Amount of deferred tax liability attributable to taxable temporary differences from contingency reserves. Compensation expense Share-based Payment Arrangement, Expense Accumulated Net Investment Gains (Losses) On Investments AOCI, Accumulated Gain (Loss), Debt Securities, Available-for-sale, Parent [Member] Counterparty Name [Axis] Counterparty Name [Axis] Investments by Consolidated and Nonconsolidated Entities [Domain] Investments by Consolidated and Nonconsolidated Entities [Domain] Common shares, $0.015 par value: Authorized - 233,333; issued and outstanding - 112,423 shares in 2020 and 98,394 shares in 2019 Common Stock, Value, Issued Document Fiscal Year Focus Document Fiscal Year Focus Ceded Ceded Premiums Written Other comprehensive income, tax effect Other Comprehensive Income (Loss), Tax, Portion Attributable to Parent Time and Performance- Based Share Awards Vesting Based On Service And Performance [Member] Represents a share based compensation award with vesting based on a combination of length of service and achievement of performance conditions. Income tax benefit Share-based Payment Arrangement, Expense, Tax Benefit Entity Current Reporting Status Entity Current Reporting Status Price per share (in dollars per shares) Sale of Stock, Price Per Share Residential and commercial mortgage securities Residential and commercial mortgage securities Residential And Commercial Mortgage Securities [Member] Residential And Commercial Mortgage Securities [Member] Related Party Transaction [Axis] Related Party Transaction [Axis] Purchase of investments available for sale Payments to Acquire Debt Securities, Available-for-sale Schedule of Long-term Debt Instruments [Table] Schedule of Long-term Debt Instruments [Table] Granted (in dollars per share) Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period, Weighted Average Grant Date Fair Value Other income Other Income Vesting (as a percent) Nonvested Common Shares Earned Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Rights, Percentage Common shares, issued (in shares) Common Stock, Shares, Issued ILN 2018 Radnor Re 2019-1 Ltd. Radnor Re 2019-1 Ltd. [Member] Radnor Re 2019-1 Ltd. [Member] Due in 1 year Debt Securities, Available-for-sale, Maturity, Allocated and Single Maturity Date, Rolling within One Year, Fair Value Present value of lease liabilities Operating Lease, Liability U.S. agency mortgage-backed securities Collateralized Mortgage Backed Securities [Member] Net deferred tax liability Deferred Tax Liabilities, Net Minimum number of votes per share for other shareholders under 9.5% shareholder provision Minimum Number Of Votes Per Share Other Shareholders Minimum Number Of Votes Per Share Other Shareholders Accounts receivable Increase (Decrease) in Accounts Receivable Debt Instrument [Line Items] Debt Instrument [Line Items] Statement of Comprehensive Income [Abstract] Statement of Comprehensive Income [Abstract] Total stockholders’ equity Stockholders equity, beginning of period Stockholders equity, end of period Stockholders' equity Stockholders' Equity Attributable to Parent Deferred policy acquisition costs Deferred Tax Liabilities, Deferred Expense, Deferred Policy Acquisition Cost Concentration Risk Type [Domain] Concentration Risk Type [Domain] Fair Value Debt Securities, Trading and Available-for-sale Total liabilities and stockholders’ equity Liabilities and Equity Loss Contingencies [Line Items] Loss Contingencies [Line Items] Accumulated other comprehensive income 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] Share Units Restricted Stock Units (RSUs) [Member] Operating lease cost Operating Lease, Cost Performance period Share Based Compensation Arrangement by Share Based Payment Award Performance Period Represents the period over which a performance condition to the award is measured, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days. Accounts receivable Financing Receivable, after Allowance for Credit Loss Credit facility borrowings Subordinated Borrowings [Abstract] Financial Instrument [Axis] Financial Instrument [Axis] Antidilutive nonvested shares (in shares) Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount Current Current Income Tax Expense (Benefit) Schedule of portion of nonvested Common Shares earned based upon achievement of compounded annual book value per share growth Schedule of Shares Earned Unvested Performance Shares [Table Text Block] Tabular disclosure of shares earned for unvested performance shares. Credit Facility [Line Items] Line of Credit Facility [Line Items] Percent change used in calculation of expense Liability For Claims And Claims Adjustment Expense, Percent Change Used In Calculation Of Expense Liability For Claims And Claims Adjustment Expense, Percent Change Used In Calculation Of Expense Short-term lease cost Short-term Lease, Cost Equity Component [Domain] Equity Component [Domain] Liabilities Liabilities [Abstract] 2019 Vintage Year 2019 [Member] Vintage Year 2019 [Member] Property and equipment (at cost, less accumulated depreciation of $60,161 in 2020 and $57,639 in 2019) Property, Plant and Equipment, Net Stock-Based Compensation Share-based Payment Arrangement [Text Block] Net income Net income Net Income (Loss) Attributable to Parent Change in: Increase (Decrease) in Operating Capital [Abstract] 2020 (October 1 through December 31) Lessee, Operating Lease, Liability, to be Paid, Remainder of Fiscal Year Schedule of Variable Interest Entities [Table] Schedule of Variable Interest Entities [Table] Compensation expense, net of forfeitures, and related tax effects recognized in connection with nonvested shares Share-based Payment Arrangement, Expensed and Capitalized, Amount [Abstract] Losses and expenses: Benefits, Losses and Expenses [Abstract] Current Fiscal Year End Date Current Fiscal Year End Date Schedule of statutory net income, statutory surplus and contingency reserve liability Statutory Accounting Practices Disclosure [Table Text Block] Earnings Per Share [Abstract] Earnings Per Share [Abstract] Gross investment income Gross Investment Income, Operating Schedule of net deferred tax (liability) asset and components Schedule of Deferred Tax Assets and Liabilities [Table Text Block] Components of net investment income Net Investment Income [Line Items] Radnor Re 2019-2 Ltd. Radnor Re 2019-2 [Member] Radnor Re 2019-2 [Member] Direct Direct Premiums Written Amortization of premium on investment securities Investment Income, Amortization of Premium Less: Reclassification adjustment for gains included in net income, before tax Reclassification from AOCI, Current Period, before Tax, Attributable to Parent Stockholders’ equity Stockholders' Equity Attributable to Parent [Abstract] Accumulated Other Comprehensive Income (Loss) [Line Items] Accumulated Other Comprehensive Income (Loss) [Line Items] Aggregate excess of loss (up to) Reinsurance, Aggreate Excess Of-Loss Reinsurance Coverage Reinsurance, Aggreate Excess Of-Loss Reinsurance Coverage Document Fiscal Period Focus Document Fiscal Period Focus Statutory net income Statutory Accounting Practices, Statutory Net Income Amount Internal Investment Grade Internal Investment Grade [Member] Supplemental Disclosure of Cash Flow Information Supplemental Cash Flow Information [Abstract] Subtotal Debt Securities, Available-for-sale, Maturity, Allocated and Single Maturity Date, Amortized Cost % of pretax income Effective Income Tax Rate Reconciliation, Percent [Abstract] Before Tax AOCI Attributable To Parent, Before Tax [Roll Forward] AOCI Attributable To Parent, Before Tax [Roll Forward] Entity Filer Category Entity Filer Category Common Shares Common Stock [Member] 2015 & 2016 Vintage Year 2015 and 2016 [Member] Vintage Year 2015 and 2016 [Member] Concentration Risk Benchmark [Domain] Concentration Risk Benchmark [Domain] Return of investment from other invested assets Proceeds from Equity Method Investment, Distribution, Return of Capital Certificate of participation bonds Certification Of Participation Bonds [Member] Represents a type of financing where an investor purchases a share of the lease revenues of a program rather than the bond being secured by those revenues. Other comprehensive income (loss): Other Comprehensive Income (Loss), before Tax, Portion Attributable to Parent [Abstract] First year retention Remaining First Layer Retention Reinsurance Retention Policy, Amount Retained Term Loan Secured Debt [Member] U.S. Treasury securities US Treasury Securities [Member] Unusual or Infrequent Item, or Both [Domain] Unusual or Infrequent Item, or Both [Domain] Due after 5 but within 10 years Debt Securities, Available-for-sale, Maturity, Allocated and Single Maturity Date, Rolling after Five Through Ten Years, Fair Value 2019 Performance-Based Grants Two Thousand Nineteen Performance-Based Grants [Member] Two Thousand Nineteen Performance-Based Grants [Member] Less than 12 months Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss Money market funds Money Market Funds [Member] Municipal debt securities Municipal debt securities Municipal Bonds [Member] Reinsurance percentage Reinsurance Retention Policy, Reinsured Risk, Percentage Accumulated depreciation Accumulated Depreciation, Depletion and Amortization, Property, Plant, and Equipment Noncash Transactions Noncash Investing and Financing Items [Abstract] Collateralized coverage legal maturities Reinsurance, Collateralized Coverage, Legal Maturities, Term Reinsurance, Collateralized Coverage, Legal Maturities, Term Net increase (decrease) in cash Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents, Period Increase (Decrease), Including Exchange Rate Effect DEUs Dividend Equivalent Unit [Member] Dividend Equivalent Unit [Member] Dilutive effect of nonvested shares (in shares) Incremental Common Shares Attributable to Dilutive Effect of Nonvested Shares with Forfeitable Dividends Loss Contingency, Nature [Domain] Loss Contingency, Nature [Domain] Schedule of lease liability maturity Lessee, Operating Lease, Liability, Maturity [Table Text Block] Effective Income Tax Rate Reconciliation, Amount Effective Income Tax Rate Reconciliation, Amount [Abstract] Reinsurance Policy [Domain] Reinsurance Policy [Domain] Amortization period Amortization Period Excess of Loss Portfolio Amortization Period Excess of Loss Portfolio Utilities Utilities Sector [Member] Utilities Sector [Member] Basic (in shares) Basic weighted average shares outstanding (in shares) Weighted Average Number of Shares Outstanding, Basic Unearned premium reserve Increase (Decrease) in Unearned Premiums Investments Investment available for sale Fair Value Debt Securities, Available-for-sale [Abstract] Number of investment securities in an unrealized loss position Debt Securities, Available-for-sale, Unrealized Loss Position, Number of Positions Prepaid federal income tax T&L Bonds held as of end of period Mortgage Guaranty Insurer United States Mortgage Guaranty Tax and Loss Bonds Represents, for a mortgage guaranty insurer, the amount of investment in United States Mortgage Guaranty Tax and Loss Bonds issued by the Treasury Department for eligibility for certain tax deductions under enacted tax laws. Loss Contingencies [Table] Loss Contingencies [Table] Direct Direct Premiums Earned Plan Name [Domain] Plan Name [Domain] Interest payments Interest Paid, Excluding Capitalized Interest, Operating Activities Fair value of investments deposited with insurance regulatory authorities Debt Securities, Available-for-sale, Restricted Technology Technology Debt Sector [Member] Technology Debt Sector [Member] Nature of Operations and Basis of Presentation Organization, Consolidation and Presentation of Financial Statements Disclosure [Text Block] Lease liabilities arising from obtaining right-of-use assets Right-of-Use Asset Obtained in Exchange for Operating Lease Liability Total revenues Revenues Current period Current Year Claims and Claims Adjustment Expense Income tax expense Total income tax expense Income Tax Expense (Benefit) Investment Income [Table] Investment Income [Table] Cash at beginning of year Cash at 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] Energy Energy Sector [Member] Energy Sector [Member] Diluted (in dollars per share) Diluted earnings per share (in dollars per share) Earnings Per Share, Diluted Variable Interest Entity [Line Items] Variable Interest Entity [Line Items] Proceeds from sales of investments available for sale Proceeds from Sale of Debt Securities, Available-for-sale Local Phone Number Local Phone Number Quota share reinsurance Quota Share Reinsurance Transaction [Member] Represents an agreement between an insurer and a reinsurer whereby the reinsurer pays an agreed-upon percentage of all losses the insurer sustains. First Vesting Period Share-based Payment Arrangement, Tranche One [Member] Quota Share Reinsurance Quota Share Reinsurance [Member] Quota Share Reinsurance [Member] Amount outstanding, gross Long-term Debt, Gross Panel of Reinsurers Panel Of Reinsurers [Member] Panel Of Reinsurers [Member] Consumer, cyclical Consumer, Cyclical Sector [Member] Consumer, Cyclical Sector [Member] Entity Address, Address Line One Entity Address, Address Line One Entity Address, Address Line Two Entity Address, Address Line Two Due after 10 years Debt Securities, Available-for-sale, Maturity, Allocated and Single Maturity Date, Rolling after 10 Years, Amortized Cost Issuance of management incentive shares Shares Issued, Value, Share-based Payment Arrangement, before Forfeiture Related Party Transaction [Domain] Related Party Transaction [Domain] Other assets Increase (Decrease) in Other Operating Assets Entity Emerging Growth Company Entity Emerging Growth Company 2017 Vintage Year 2017 [Member] Vintage Year 2017 SEC Schedule, 12-17, Insurance Companies, Reinsurance [Table] SEC Schedule, 12-17, Insurance Companies, Reinsurance [Table] Deferred income tax provision Deferred Deferred Income Tax Expense (Benefit) Accrued investment income Accrued Investment Income Receivable Credit facility, maximum borrowing capacity Line of Credit Facility, Maximum Borrowing Capacity Award Type [Axis] Award Type [Axis] Weighted Average Grant Date Fair Value Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value [Abstract] Decrease in unearned premiums (Increase) Decrease in Unearned Premiums, Net Dividends Restrictions Dividend Payment Restrictions [Text Block] Total fair value of shares vested Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Vested in Period, Fair Value Financial Financial Sector [Member] Financial Sector [Member] Maximum Maximum [Member] Nonvested shares Deferred Tax Assets, Tax Deferred Expense, Compensation and Benefits, Share-based Compensation Cost Retained Earnings Retained Earnings [Member] Add provision for losses and LAE, net of reinsurance, occurring in: Liability for Unpaid Claims and Claims Adjustment Expense, Incurred Claims [Abstract] Statutory Accounting Statutory Accounting Disclosure [Text Block] Represents the entire disclosure pertaining to the statutory accounting. Total income tax expense Effective income tax rate Effective Income Tax Rate Reconciliation, Percent Net cash used in investing activities Net Cash Provided by (Used in) Investing Activities Fair value of the required investments on deposit in trusts Assets Held-in-trust Subtotal Debt Securities, Available-for-sale, Maturity, Allocated and Single Maturity Date, Fair Value Schedule of Share-based Compensation Arrangements by Share-based Payment Award [Table] Schedule of Share-based Compensation Arrangements by Share-based Payment Award [Table] Award Type [Domain] Award Type [Domain] Investments [Domain] Investments [Domain] Corporate debt securities Corporate Debt Securities [Member] Trading Symbol Trading Symbol 2018 Vintage Year 2018 [Member] Vintage Year 2018 Accumulated Other Comprehensive Income (Loss) [Table] Accumulated Other Comprehensive Income (Loss) [Table] Unrealized holding gains arising during the period, before tax OCI, before Reclassifications, before Tax, Attributable to Parent Other information: Lessee, Operating Lease, Description [Abstract] Fair Value, by Balance Sheet Grouping [Table] Fair Value, by Balance Sheet Grouping [Table] Unearned premium reserve Deferred Tax Assets, Tax Deferred Expense, Reserves and Accruals, Unearned Premiums Reserve 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] Schedule of reconciliation of beginning and ending reserve balances for losses and loss adjustment expenses (LAE) Schedule of Liability for Unpaid Claims and Claims Adjustment Expense [Table Text Block] General obligation bonds General Obligation Municipal Bonds [Member] A bond secured by a pledge of the issuer's taxing powers (limited or unlimited). More commonly the general obligation bonds of local governments are paid from ad valorem property taxes and other general revenues. Considered the most secure of all municipal debt. Financing Activities Net Cash Provided by (Used in) Financing Activities, Continuing Operations [Abstract] Entity Shell Company Entity Shell Company Fair Value, Measurements, Recurring Fair Value, Recurring [Member] Shares tendered by employees to pay employee withholding taxes (in shares) Share-based Payment Arrangement, Shares Withheld for Tax Withholding Obligation Net premiums earned Premiums Earned, Net Proceeds Proceeds from Lines of Credit Recently Issued Accounting Standards New Accounting Pronouncements, Policy [Policy Text Block] Statement of Financial Position [Abstract] Statement of Financial Position [Abstract] Dividends Restrictions Statutory Accounting Practices [Line Items]