Business Combinations [Abstract] Triad Transaction Business Combination Disclosure [Text Block] Accounting Policies [Abstract] Insurance Premium Revenue Recognition Revenue Recognition [Abstract] Earned premiums from mortgage guaranty insurance monthly policies as a percentage of total earned premiums (percent) Mortgage Guaranty Insurance Contracts Monthly Policies Earned Premium Percentage of Total Represents the earned premium during the period from mortgage guaranty insurance contracts which provide for monthly payments as a percentage of total earned premium. Threshold coverage period for single premium primary mortgage insurance policies (in years) Primary Mortgage Guaranty Insurance Contracts Single Premium Policies Threshold Period of Coverage Represents the threshold period of coverage for primary mortgage insurance policies to be referred to as single premium policies. Unearned single premium recognized as earned upon notice of policy cancellation due to repayment of insured loan by borrower Non-refundable, Single Premium Primary Mortgage Insurance, Unearned Premium Recognized as Earned upon Cancellation due to Loan Repayment Represents, for single premium primary mortgage insurance policies with a nonrefundable premium, the total amount of unearned premium recognized as earned premium upon notification of cancellation due to repayment of the insured loan by the borrower. Capital [Abstract] Capital Stock Stockholders' Equity Note Disclosure [Text Block] Liability for Future Policy Benefits and Unpaid Claims and Claims Adjustment Expense [Abstract] Incurred claims and claim adjustment expenses Liability for Unpaid Claims and Claims Adjustment Expense, Claims Paid, Prior Years Favorable prior year development Prior Year Claims and Claims Adjustment Expense 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. Number of loans in default increase (decrease) during period Number Of Loans In Default Increase (Decrease) During Period Number of Loans in Default Increase (Decrease) During Period Number of loans in hurricane impacted areas in default increase (decrease) during period Number Of Loans In Hurricane Impacted Areas In Default Increase (Decrease) During Period Number Of Loans In Hurricane Impacted Areas In Default Increase (Decrease) During Period Liability for Claims and Claims Adjustment Expense [Table] Liability for Claims and Claims Adjustment Expense [Table] Catastrophic Event [Axis] Catastrophic Event [Axis] Catastrophic Event [Domain] Catastrophic Event [Domain] Hurricane Hurricane [Member] Liability for Claims and Claims Adjustment Expense [Line Items] Liability for Claims and Claims Adjustment Expense [Line Items] Reserve for losses and defaults Liability for Claims and Claims Adjustment Expense Disclosure of Compensation Related Costs, Share-based Payments [Abstract] Compensation expense Allocated Share-based Compensation Expense Income tax benefit Employee Service Share-based Compensation, Tax Benefit from Compensation Expense Insurance Ratios [Abstract] Capital Maintenance Agreement Capital Maintenance Agreement Disclosure [Text Block] The entire disclosure for the capital maintenance agreement under which the entity guaranty agreed to contribute funds, under specified conditions. Statement of Financial Position [Abstract] Assets Assets [Abstract] Investments available for sale, at fair value Available-for-sale Securities [Abstract] Fixed maturities (amortized cost: 2017 — $1,994,200; 2016 — $1,497,186) Marketable Securities, Fixed Maturities Short-term investments (amortized cost: 2017 — $312,714; 2016 — $132,352) Short-term Investments Total investments Investments Cash Cash Accrued investment income Accrued Investment Income Receivable Accounts receivable Accounts Receivable, Net Deferred policy acquisition costs Deferred Policy Acquisition Costs Property and equipment (at cost, less accumulated depreciation of $50,466 in 2017 and $46,543 in 2016) Property, Plant and Equipment, Net Prepaid federal income tax 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. Other assets Other Assets Total assets Assets Liabilities and Stockholders' Equity Liabilities and Equity [Abstract] Liabilities Liabilities [Abstract] Reserve for losses and LAE Liability for Unpaid Claims and Claims Adjustment Expense, Net Unearned premium reserve Unearned Premiums Net deferred tax liability Deferred Tax Liabilities, Net Credit facility borrowings (at carrying value, less unamortized deferred costs of $1,409 in 2017 and $0 in 2016) Long-term Line of Credit Securities purchases payable Investment-related Liabilities Other accrued liabilities Other Accrued Liabilities Total liabilities Liabilities Commitments and contingencies (see Note 8) Commitments and Contingencies Stockholders' Equity Stockholders' Equity Attributable to Parent [Abstract] Common Shares, $0.015 par value: Authorized - 233,333; issued and outstanding - 98,434 shares in 2017 and 93,105 shares in 2016 Common Stock, Value, Issued Additional paid-in capital Additional Paid in Capital, Common Stock Accumulated other comprehensive loss Accumulated Other Comprehensive Income (Loss), Net of Tax Retained earnings Retained Earnings (Accumulated Deficit) Total stockholders' equity Stockholders' Equity Attributable to Parent Total liabilities and stockholders' equity Liabilities and Equity Condensed Financial Information of Parent Company Only Disclosure [Abstract] Condensed Balance Sheet Statement [Table] Condensed Balance Sheet Statement [Table] Consolidated Entities [Axis] Consolidated Entities [Axis] Consolidated Entities [Domain] Consolidated Entities [Domain] Parent Company Parent Company [Member] Balance Sheets Condensed Balance Sheet Statements, Captions [Line Items] Investments Fixed maturities (amortized cost: 2017 — $0; 2016 — $10,002) Short-term investments (amortized cost: 2017 — $97,926; 2016 — $32,039) Due from affiliates Due from Affiliates Investment in consolidated subsidiaries Equity Method Investments Liabilities and stockholders' equity Credit facility borrowings (at carrying value, less unamortized deferred costs of $1,409 in 2017 and $0 in 2016) Commitments and contingencies Common shares Short-duration Insurance Contracts, Accident Year [Axis] Short-duration Insurance Contracts, Accident Year [Axis] Short-duration Insurance Contracts, Accident Year [Domain] Short-duration Insurance Contracts, Accident Year [Domain] 2010 Short-duration Insurance Contracts, Accident Year 2010 [Member] 2011 Short-duration Insurance Contracts, Accident Year 2011 [Member] 2012 Short-duration Insurance Contracts, Accident Year 2012 [Member] 2013 Short-duration Insurance Contracts, Accident Year 2013 [Member] 2014 Short-duration Insurance Contracts, Accident Year 2014 [Member] 2015 Short-duration Insurance Contracts, Accident Year 2015 [Member] 2016 Short-duration Insurance Contracts, Accident Year 2016 [Member] 2017 Short-duration Insurance Contracts, Accident Year 2017 [Member] Products and Services [Axis] Products and Services [Axis] Products and Services [Domain] Products and Services [Domain] Property Insurance Product Line Property Insurance Product Line [Member] Incurred Loss and Allocated LAE, For the Years Ended December 31, Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net Total of IBNR plus Expected Development on Reported Defaults Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net Cumulative Number of Reported Defaults Short-duration Insurance Contracts, Number of Reported Claims Cumulative Paid Losses and Allocated LAE For the Years Ended December 31, Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net All outstanding liabilities before 2010, net of reinsurance Short-duration Insurance Contracts, Liability for Unpaid Claims and Allocated Claim Adjustment Expense, Net, Not Separately Presented Reserve for losses and LAE, net of reinsurance Condensed Income Statement [Table] Condensed Income Statement [Table] Condensed Statements of Comprehensive Income (Loss) Condensed Income Statements, Captions [Line Items] Revenues: Revenues [Abstract] Net investment income Net Investment Income Realized investment (losses) gains, net Available-for-sale Securities, Gross Realized Gain (Loss), Excluding Other than Temporary Impairments Administrative service fees from subsidiaries Revenue from Related Parties Total revenues Revenues Expenses: Operating Expenses [Abstract] Administrative service fees to subsidiaries Related Party Transaction, Selling, General and Administrative Expenses from Transactions with Related Party Other operating expenses Other Cost and Expense, Operating Interest expense Interest Expense Total expenses Operating Expenses Income before income taxes Income (Loss) from Continuing Operations before Equity Method Investments, Income Taxes, Noncontrolling Interest Loss before equity in undistributed net income of subsidiaries Income (Loss) from Continuing Operations before Income (Loss) from Equity Method Investments Represents the income or loss from continuing operations attributable to the economic entity which may also be defined as revenue less expenses and taxes from ongoing operations before income or loss from equity method investments. Equity in undistributed net income of subsidiaries Income (Loss) from Subsidiaries, Net of Tax Net income Net Income (Loss) Attributable to Parent Other comprehensive income (loss): Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Parent [Abstract] Change in unrealized appreciation (depreciation) of investments, net of tax expense (benefit) of $4,519 in 2017, ($2,941) in 2016 and ($1,285) in 2015 Other Comprehensive Income (Loss), Available-for-sale Securities Adjustment, Net of Tax, Portion Attributable to Parent Change in unrealized appreciation (depreciation) of investments, tax expense (benefit) Other Comprehensive Income (Loss), Available-for-sale Securities, Tax, Portion Attributable to Parent Total other comprehensive income (loss) Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Parent Comprehensive income Comprehensive Income (Loss), Net of Tax, Attributable to Parent Fair Value Disclosures [Abstract] Fair Value Measurements, Recurring and Nonrecurring [Table] Fair Value Measurements, Recurring and Nonrecurring [Table] Measurement Frequency [Axis] Measurement Frequency [Axis] Fair Value, Measurement Frequency [Domain] Fair Value, Measurement Frequency [Domain] Recurring basis Fair Value, Measurements, Recurring [Member] Fair Value, Hierarchy [Axis] Fair Value, Hierarchy [Axis] Fair Value Hierarchy [Domain] Fair Value Hierarchy [Domain] Significant Unobservable Inputs (Level 3) Fair Value, Inputs, Level 3 [Member] Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] Assets at fair value Assets, Fair Value Disclosure Commitments and Contingencies Disclosure [Abstract] Commitments and Contingencies Commitments and Contingencies Disclosure [Text Block] Statutory Accounting Practices, Statutory Amount Available for Dividend Payments [Abstract] Dividends Restrictions Dividend Payment Restrictions [Text Block] Schedule of Related Party Transactions, by Related Party [Table] Schedule of Related Party Transactions, by Related Party [Table] Legal Entity [Axis] Legal Entity [Axis] Entity [Domain] Entity [Domain] 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. 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. Related Party Transaction [Axis] Related Party Transaction [Axis] Related Party Transaction [Domain] Related Party Transaction [Domain] Capital maintenance agreement Capital Maintenance Agreement [Member] Represents an agreement between two wholly-owned insurance subsidiaries of a common parent for one subsidiary to contribute funds, under specified conditions, to maintain the other subsidiary's risk to capital ratio at or below a level, as specified in the agreement, in return for a surplus note. Related Party [Axis] Related Party [Axis] Related Party [Domain] Related Party [Domain] Range [Axis] Range [Axis] Range [Domain] Range [Domain] Maximum Maximum [Member] Capital Maintenance Agreement Related Party Transaction [Line Items] Risk to capital ratio Risk to Capital Ratio Represents an entity's ratio of net risk in force to the amount of statutory capital, as defined under insurance regulations. Amounts outstanding Notes Receivable, Related Parties Schedule II-Condensed Financial Information of Registrant Condensed Financial Information of Parent Company Only Disclosure [Text Block] Statement of Comprehensive Income [Abstract] Net premiums written Premiums Written, Net Increase in unearned premiums (Increase) Decrease in Unearned Premiums, Net Net premiums earned Premiums Earned, Net Realized investment gains, net Realized Investment Gains (Losses) Other income Other Income Losses and expenses: Benefits, Losses and Expenses [Abstract] Provision for losses and LAE Liability for Unpaid Claims and Claims Adjustment Expense, Incurred Claims 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. Total losses and expenses Benefits, Losses and Expenses Income tax expense Income Tax Expense (Benefit) Earnings per share: Earnings Per Share, Basic and Diluted [Abstract] Basic (in dollars per share) Earnings Per Share, Basic Diluted (in dollars per share) Earnings Per Share, Diluted Weighted average common shares outstanding: Weighted Average Number of Shares Outstanding, Diluted [Abstract] Basic (in shares) Weighted Average Number of Shares Outstanding, Basic Diluted (in shares) Weighted Average Number of Shares Outstanding, Diluted Net income Net Income (Loss) Available to Common Stockholders, Basic Other comprehensive income (loss): Change in unrealized appreciation (depreciation) of investments, net of tax expense (benefit) of $4,519 in 2017, ($2,941) in 2016 and ($1,285) in 2015 Stock-Based Compensation Disclosure of Compensation Related Costs, Share-based Payments [Text Block] Quoted Prices in Active Markets for Identical Instruments (Level 1) Fair Value, Inputs, Level 1 [Member] Significant Other Observable Inputs (Level 2) Fair Value, Inputs, Level 2 [Member] Investment Issuer [Axis] Investment Issuer [Axis] Investment Issuer [Domain] Investment Issuer [Domain] U.S. Agency US Government Corporations and Agencies Securities [Member] Major Types of Debt and Equity Securities [Axis] Major Types of Debt and Equity Securities [Axis] Major Types of Debt and Equity Securities [Domain] Major Types of Debt and Equity Securities [Domain] U.S. Treasury securities US Treasury Securities [Member] U.S. agency securities US Government Agencies Debt Securities [Member] U.S. agency mortgage-backed securities Collateralized Mortgage Backed Securities [Member] Municipal debt securities Municipal Bonds [Member] Corporate debt securities Corporate Debt Securities [Member] Residential and commercial mortgage securities Residential And Commercial Mortgage Securities [Member] Residential And Commercial Mortgage Securities [Member] Asset-backed securities Asset-backed Securities [Member] Money market funds Money Market Funds [Member] Recurring fair value measurements Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract] Fair Value Available-for-sale Securities Total assets at fair value Reserve for Losses and Loss Adjustment Expenses Liability for Claims and Claims Adjustment Expense [Abstract] Number of consecutive missed loan payments by borrower for classification of insured loan as in default Liability for Unpaid Claims and Claims Adjustment Expense, Number of Consecutive Missed Loan Payments for Classification of Loan as in Default Represents, for purposes of establishing loss reserves for future claims on insured loans, the number of consecutive payments missed by the borrower for classification of the loan as in default. Premium Deficiency Reserve Insurance Loss Reserves [Abstract] Premium deficiency reserve Premium Deficiency Reserve Represents the amount of reserve for the excess of the net present value of expected future losses and expenses for a particular group of policies over the net present value of expected future premium, anticipated investment income and existing reserves for that specified group of policies. Accumulated Other Comprehensive Income (Loss), Net of Tax [Abstract] Accumulated Other Comprehensive Income (Loss) Comprehensive Income (Loss) Note [Text Block] Quarterly Financial Information Disclosure [Abstract] Summary of unaudited quarterly results of operations Quarterly Financial Information [Table Text Block] Investments, Debt and Equity Securities [Abstract] Investment Income [Table] Investment Income [Table] Investment Type [Axis] Investment Type [Axis] Investments [Domain] Investments [Domain] Fixed maturities Fixed Maturities [Member] Short-term investments Short-term Investments [Member] Components of net investment income Net Investment Income [Line Items] Gross investment income Gross Investment Income, Operating Investment expenses Investment Income, Investment Expense Net investment income Schedule of Available-for-sale Securities [Table] Schedule of Available-for-sale Securities [Table] Investments available for sale Schedule of Available-for-sale Securities [Line Items] Amortized Cost Available-for-sale Securities, Amortized Cost Basis Unrealized Gains Available-for-sale Securities, Accumulated Gross Unrealized Gain, before Tax Unrealized Losses Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax 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] Schedule of changes during period in Level 3 liabilities measured at fair value on a recurring basis, and realized and unrealized losses (gains) related to Level 3 liabilities Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Table Text Block] Accumulated Other Comprehensive Income (Loss) [Table] Accumulated Other Comprehensive Income (Loss) [Table] Equity Components [Axis] Equity Components [Axis] Equity Component [Domain] Equity Component [Domain] Accumulated Other Comprehensive Income (Loss) AOCI Attributable to Parent [Member] Accumulated Net Investment Gain (Loss) Attributable to Parent Accumulated Net Investment Gain (Loss) Attributable to Parent [Member] Accumulated Other Comprehensive Income (Loss) [Line Items] Accumulated Other Comprehensive Income (Loss) [Line Items] Before Tax AOCI Attributable To Parent, Before Tax [Roll Forward] AOCI Attributable To Parent, Before Tax [Roll Forward] AOCI before tax, beginning of period AOCI before Tax, Attributable to Parent Other comprehensive income (loss): Other Comprehensive Income (Loss), before Tax, Portion Attributable to Parent [Abstract] Unrealized holding gains (losses) arising during the period, before tax OCI, before Reclassifications, before Tax, Attributable to Parent Less: Reclassification adjustment for gains included in net income, before tax Reclassification from AOCI, Current Period, before Tax, Attributable to Parent Other comprehensive income (loss), before tax Other Comprehensive Income (Loss), before Tax, Portion Attributable to Parent AOCI before tax, end of period Tax Effect AOCI Attributable To Parent, Tax [Roll Forward] AOCI Attributable To Parent, Tax AOCI tax effect, beginning of period AOCI Tax, Attributable to Parent Other comprehensive income (loss): Other Comprehensive Income (Loss), Tax, Portion Attributable to Parent, Parenthetical Disclosures [Abstract] Unrealized holding (gains) losses arising during the period, tax effect Other Comprehensive Income (Loss) before Reclassifications, Tax Less: Reclassification adjustment for gains included in net income, tax effect Reclassification from AOCI, Current Period, Tax Other comprehensive income (loss), tax effect Other Comprehensive Income (Loss), Tax, Portion Attributable to Parent AOCI tax effect, end of period Net of Tax AOCI Attributable to Parent, Net of Tax [Roll Forward] Stockholders equity, beginning of period Unrealized holding gains (losses) arising during the period, net of tax OCI, before Reclassifications, Net of Tax, Attributable to Parent Less: Reclassification adjustment for gains included in net income, net of tax Reclassification from AOCI, Current Period, Net of Tax, Attributable to Parent Reclassification of certain income tax effects resulting from tax reform Tax Cuts And Jobs Act Of 2017, Reclassification From AOCI To Retained Earnings Tax Cuts And Jobs Act of 2017, Reclassification From AOCI To Retained Earnings Stockholders equity, end of period Average Annual Percentage Payout of Incurred Losses and Allocated LAE by Year Liability for Unpaid Claims and Claims Adjustment Expense, Activity in Liability [Abstract] Year 1 Short-duration Insurance Contracts, Historical Claims Duration, Year One Year 2 Short-duration Insurance Contracts, Historical Claims Duration, Year Two Year 3 Short-duration Insurance Contracts, Historical Claims Duration, Year Three Year 4 Short-duration Insurance Contracts, Historical Claims Duration, Year Four Year 5 Short-duration Insurance Contracts, Historical Claims Duration, Year Five Year 6 Short-duration Insurance Contracts, Historical Claims Duration, Year Six 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. Summary of nonvested Common Share and nonvested Common Share unit activity Schedule of Share-based Compensation, Restricted Stock and Restricted Stock Units Activity [Table Text Block] Schedule of compensation expense, net of forfeitures, and related tax effects recognized in connection with nonvested shares Schedule of Compensation Cost for Share-based Payment Arrangements, Allocation of Share-based Compensation Costs by Plan [Table Text Block] Fair Value of Financial Instruments Fair Value Disclosures [Text Block] Insurance [Abstract] Schedule of statutory net income, statutory surplus and contingency reserve liability Statutory Accounting Practices Disclosure [Table Text Block] Earnings Per Share [Abstract] 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] Quarterly Financial Data (Unaudited) Quarterly Financial Information [Text Block] Income Tax Disclosure [Abstract] Schedule of components of income tax expense Schedule of Components of Income Tax Expense (Benefit) [Table Text Block] 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] Schedule of net deferred tax (liability) asset and components Schedule of Deferred Tax Assets and Liabilities [Table Text Block] Schedule of balances by type of long-lived assets Property, Plant and Equipment [Table Text Block] Schedule of Business Acquisitions, by Acquisition [Table] Schedule of Business Acquisitions, by Acquisition [Table] Business Acquisition [Axis] Business Acquisition [Axis] Business Acquisition, Acquiree [Domain] Business Acquisition, Acquiree [Domain] Triad Assets Triad Guaranty Incorporated And Triad Guaranty Insurance Corporation Assets And Contractual Obligations [Member] Represents the assets purchased and the assumption of certain contractual obligations from Triad Guaranty Inc. and its wholly-owned subsidiary Triad Guaranty Insurance Corporation (collectively Triad) under the terms of an asset purchase agreement. Other Commitments [Axis] Other Commitments [Axis] Other Commitments [Domain] Other Commitments [Domain] Fixed payment purchase price obligation Fixed Payment Obligation To Seller [Member] Represents the fixed payment obligation to seller in a purchase transaction. Type of Arrangement and Non-arrangement Transactions [Axis] Type of Arrangement and Non-arrangement Transactions [Axis] Arrangements and Non-arrangement Transactions [Domain] Arrangements and Non-arrangement Transactions [Domain] Services Agreement Service Agreement [Member] Represents an agreement to provide services to another party. Counterparty Name [Axis] Counterparty Name [Axis] Counterparty Name [Domain] Counterparty Name [Domain] Triad Triad Guaranty Incorporated And Triad Guaranty Insurance Corporation [Member] Represents information pertaining to Triad Guaranty Inc. together with its wholly-owned subsidiary Triad Guaranty Insurance Corporation (collectively, Triad). Income Statement Location [Axis] Income Statement Location [Axis] Income Statement Location [Domain] Income Statement Location [Domain] Other income Other Income [Member] Triad Transaction Business Acquisition [Line Items] Payment obligation Contractual Obligation Contingent payments Business Combination, Contingent Consideration Arrangements, Range of Outcomes, Value, High Services agreement Business Combination, Separately Recognized Transactions [Abstract] Fees earned under Services Agreement Sales Revenue, Services, Net 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] Schedule of Share-based Compensation Arrangements by Share-based Payment Award [Table] Schedule of Share-based Compensation Arrangements by Share-based Payment Award [Table] Vesting Criteria [Axis] Vesting Criteria [Axis] Information about the type of vesting for share-based compensation awards. Vesting Criteria [Domain] Vesting Criteria [Domain] The types of vesting specified for share-based compensation awards. 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. Time-Based Share Awards Vesting Based On Service [Member] Represents a share based compensation award with vesting based on length of service. Award Type [Axis] Award Type [Axis] Equity Award [Domain] Equity Award [Domain] Nonvested shares Restricted Stock [Member] Nonvested share units Restricted Stock Units (RSUs) [Member] Stock-based compensation Share-based Compensation Arrangement by Share-based Payment Award [Line Items] Number of Shares Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward] Outstanding at beginning of year (in shares) Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number Granted (in shares) Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period Vested (in shares) Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Vested in Period Forfeited (in shares) Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Forfeited in Period Outstanding at end of period (in shares) 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] Outstanding at beginning of year (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 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 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 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 Outstanding at end of period (in dollars per share) Statement of Cash Flows [Abstract] Operating Activities Net Cash Provided by (Used in) Operating Activities, Continuing Operations [Abstract] Net income 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] Gain on the sale of investments, net Depreciation and amortization Depreciation, Depletion and Amortization Stock-based compensation expense Share-based Compensation Amortization of premium on investment securities Investment Income, Amortization of Premium Deferred income tax provision Deferred Income Tax Expense (Benefit) Change in: Increase (Decrease) in Operating Capital [Abstract] Accrued investment income Increase (Decrease) in Accrued Investment Income Receivable Accounts receivable Increase (Decrease) in Accounts Receivable Deferred policy acquisition costs Increase (Decrease) in Deferred Policy Acquisition Costs Prepaid federal income tax 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. Other assets Increase (Decrease) in Other Operating Assets Reserve for losses and LAE Increase (Decrease) in Liability for Claims and Claims Adjustment Expense Reserve Unearned premium reserve Increase (Decrease) in Unearned Premiums Other accrued liabilities Increase (Decrease) in Accrued Liabilities Net cash provided by operating activities Net Cash Provided by (Used in) Operating Activities Investing Activities Net Cash Provided by (Used in) Investing Activities, Continuing Operations [Abstract] Net change in short-term investments Payments for (Proceeds from) Short-term Investments Purchase of investments available for sale Payments to Acquire Available-for-sale Securities Proceeds from maturity of investments available for sale Proceeds from Maturities, Prepayments and Calls of Available-for-sale Securities Proceeds from sales of investments available for sale Proceeds from Sale of Available-for-sale Securities Purchase of property and equipment Payments to Acquire Property, Plant, and Equipment Net cash used in investing activities Net Cash Provided by (Used in) Investing Activities Financing Activities Net Cash Provided by (Used in) Financing Activities, Continuing Operations [Abstract] Issuance of common shares, net of costs Proceeds from Issuance of Common Stock Credit facility borrowings Proceeds from Long-term Lines of Credit Credit facility repayments Repayments of Lines of Credit Treasury stock acquired Payments for Repurchase of Common Stock Payment of issuance costs for credit facility Payments of Debt Issuance Costs Other financing activities Proceeds from (Payments for) Other Financing Activities Net cash provided by (used in) financing activities Net Cash Provided by (Used in) Financing Activities Net increase in cash Cash and Cash Equivalents, Period Increase (Decrease) Cash at beginning of year Cash and Cash Equivalents, at Carrying Value Cash at end of year Supplemental Disclosure of Cash Flow Information Supplemental Cash Flow Information [Abstract] Income tax payments Income Taxes Paid, Net Interest payments Interest Paid Noncash Transactions Noncash Investing and Financing Items [Abstract] Repayment of borrowings with term loan proceeds (see Note 7) Repayment Of Borrowing With Proceeds From Debt Repayment Of Borrowing With Proceeds From Debt Condensed Financial Statements [Table] Condensed Financial Statements [Table] Credit Facility [Axis] Credit Facility [Axis] Credit Facility [Domain] Credit Facility [Domain] Revolving Credit Facility Revolving Credit Facility [Member] Term Loan Secured Debt [Member] Uncommitted Line Uncommitted Line of Credit [Member] Uncommitted Line of Credit Essent PA Essent PA [Member] Essent PA [Member] Condensed Financial Information of Registrant Condensed Financial Statements, Captions [Line Items] Dividend payment ability, period of payment of dividends (in months) Statutory Accounting Practices, Statutory Amount Available for Dividend Payments without Regulatory Approval, Dividend Payment Period Represents the period of payment of dividends that can be declared or paid without approval of regulatory agency. Dividend payment ability, as a percentage of preceding year-end statutory policyholders' surplus Statutory Accounting Practices, Statutory Amount Available For Dividend Payments Without Regulatory Approval, Previous Fiscal Year End Statutory Policyholders Surplus Percentage Represents the amount of dividends that can be declared or paid without approval of regulatory agency, as a percentage of the previous fiscal year end statutory policyholders' surplus. Unassigned surplus Dividend Payments Restrictions Schedule, Statutory Capital and Surplus Dividends paid to parent company Cash Dividends Paid to Parent Company by Consolidated Subsidiaries Credit facility, term Debt Instrument, Term Credit facility, maximum borrowing capacity Line of Credit Facility, Maximum Borrowing Capacity Realized gross gains and losses on the sale of investments available for sale Available-for-sale Securities, Gross Realized Gain (Loss), Disclosures [Abstract] Realized gross gains Available-for-sale Securities, Gross Realized Gains Realized gross losses Available-for-sale Securities, Gross Realized Losses 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. Fair Value Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value [Abstract] Less than 12 months Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value 12 months or more Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value Total Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value Gross Unrealized Losses Available-for-sale Securities, Continuous Unrealized Loss Position, Aggregate Loss [Abstract] Less than 12 months Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss 12 months or more Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss Total Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss Other information Available-for-sale Securities, Other Disclosure Items [Abstract] Other-than-temporary impairments Other than Temporary Impairment Losses, Investments, Available-for-sale Securities Fair value of investments deposited with insurance regulatory authorities Available-for-sale Securities, Restricted Fair value of the required investments on deposit in trusts Assets Held-in-trust Debt Disclosure [Abstract] Line of Credit Facility [Table] Line of Credit Facility [Table] Credit Facility [Line Items] Line of Credit Facility [Line Items] Credit facility, commitment fee rate Line of Credit Facility, Commitment Fee Percentage Credit facility borrowings Weighted average interest rate during period Debt, Weighted Average Interest Rate Less: Common Shares dividends declared Dividends Undistributed net income Undistributed Earnings, Basic Net income allocable to Common Undistributed Earnings (Loss) Allocated to Participating Securities, Basic Basic earnings per share (in dollars per share) Diluted earnings per share (in dollars per share) Basic weighted average Common Shares outstanding (in shares) Dilutive effect of nonvested shares (in shares) Incremental Common Shares Attributable to Dilutive Effect of Nonvested Shares with Forfeitable Dividends Diluted weighted average Common Shares outstanding (in shares) Investments Available for Sale Investments in Debt and Marketable Equity Securities (and Certain Trading Assets) Disclosure [Text Block] Net deferred tax asset Deferred Tax Assets, Net [Abstract] Deferred tax assets Deferred Tax Assets, Gross Deferred tax liabilities Deferred Tax Liabilities, Gross Net deferred tax liability Components of the net deferred tax asset Components of Deferred Tax Assets and Liabilities [Abstract] Contingency reserves Deferred Tax Liabilities Contingency Reserves Amount of deferred tax liability attributable to taxable temporary differences from contingency reserves. Unearned premium reserve Deferred Tax Assets, Tax Deferred Expense, Reserves and Accruals, Unearned Premiums Reserve Nonvested shares Deferred Tax Assets, Tax Deferred Expense, Compensation and Benefits, Share-based Compensation Cost Deferred policy acquisition costs Deferred Tax Liabilities, Deferred Expense, Deferred Policy Acquisition Cost Unearned ceding commissions Deferred Tax Assets, Deferred Expense, Unearned Ceding Commissions Deferred Tax Assets, Deferred Expense, Unearned Ceding Commissions Fixed assets Deferred Tax Assets, Property, Plant and Equipment 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. Unrealized (gain) loss on investments Deferred Tax Liabilities, Other Comprehensive Income Unrealized (gain) loss on investments Deferred Tax Assets, Other Comprehensive Loss 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. Loss reserves Deferred Tax Assets, Tax Deferred Expense, Reserves and Accruals, Loss Reserves Prepaid expenses Deferred Tax Liabilities, Prepaid Expenses 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. Level 3 Liabilities Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward] Fair value of derivative liabilities at beginning of period Fair Value, Measurement with Unobservable Inputs Reconciliations, Recurring Basis, Liability Value Net realized and unrealized losses (gains) included in income Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Liability, Gain (Loss) Included in Earnings Other comprehensive (income) loss Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Liability, Gain (Loss) Included in Other Comprehensive Income (Loss) Purchases, sales, issues and settlements, net Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Liability, Purchases, (Sales), Issuances, (Settlements) Gross transfers in Fair Value, Measurement with Unobservable Inputs Reconciliation, Liability, Transfers Into Level 3 Gross transfers out Fair Value, Measurement with Unobservable Inputs Reconciliation, Liability, Transfers out of Level 3 Fair value of derivative liabilities at end of period Changes in net unrealized losses (gains) included in income on instruments held at end of period Fair Value, Liabilities Measured on Recurring Basis, Change in Unrealized Gain (Loss) Condensed Cash Flow Statement [Table] Condensed Cash Flow Statement [Table] Condensed Statements of Cash Flows Condensed Cash Flow Statements, Captions [Line Items] Net income Equity in net income of subsidiaries Loss (gain) on the sale of investments, net Changes in assets and liabilities: Other accrued liabilities Increase (Decrease) in Other Accrued Liabilities Net change in short-term investments Investments in subsidiaries Payments to Acquire Equity Method Investments Repayment of borrowings with term loan proceeds (see Note C) Organization, Consolidation and Presentation of Financial Statements [Abstract] Schedule of Collaborative Arrangements and Non-collaborative Arrangement Transactions [Table] Schedule of Collaborative Arrangements and Non-collaborative Arrangement Transactions [Table] Affiliated Entity Affiliated Entity [Member] 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. 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. Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items] Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items] Residential mortgage down payment percentage for which mortgage insurance is generally required (percent) (less than) Loans and Leases 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. Number of states in which the entity is licensed to write mortgage insurance Number of States in which Entity Operates Reinsurance percentage Reinsurance Retention Policy, Reinsured Risk, Percentage Reinsurance for mortgage insurance coverage threshold (as a percent) Reinsurance Retention Policy, Reinsured Risk, Percentage Threshold Threshold percentage of risk reinsured on insurance products per entity policy. Statement of Stockholders' Equity [Abstract] Statement [Table] Statement [Table] Common Shares Common Stock [Member] Additional Paid-In Capital Additional Paid-in Capital [Member] Retained Earnings Retained Earnings [Member] Treasury Stock Treasury Stock [Member] Statement Statement [Line Items] Changes in Stockholders' Equity Increase (Decrease) in Stockholders' Equity [Roll Forward] Net income Other comprehensive income (loss) Issuance of Common Shares, net of issuance cost of $1,802 Stock Issued During Period, Value, New Issues Issuance of management incentive shares Stock Issued During Period, Value, Share-based Compensation, Gross Forfeiture of management incentive shares Stock Issued During Period, Value, Share-based Compensation, Forfeited Stock-based compensation expense Adjustments to Additional Paid in Capital, Share-based Compensation, Requisite Service Period Recognition Cumulative effect of ASU 2016-09 adoption Cumulative Effect of New Accounting Principle in Period of Adoption Excess tax benefits from stock-based compensation expense Adjustments to Additional Paid in Capital, Income Tax Benefit from Share-based Compensation Treasury stock acquired Treasury Stock, Value, Acquired, Cost Method Cancellation of treasury stock Treasury Stock, Retired, Cost Method, Amount Other equity transactions Adjustments to Additional Paid in Capital, Other Reclassification of certain income tax effects resulting from tax reform Reserve for Losses and Loss Adjustment Expenses Liability for Future Policy Benefits and Unpaid Claims Disclosure [Text Block] Schedule of Capitalization, Equity [Table] Schedule of Capitalization, Equity [Table] Minimum Minimum [Member] Equity Schedule of Capitalization, Equity [Line Items] Total equity 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] Performance-based share awards Performance Shares [Member] EPS calculation Earnings Per Share, Diluted, by Common Class, Including Two Class Method [Line Items] Contingently issuable awards Incremental Weighted Average Shares Attributable to Dilutive Effect [Abstract] Antidilutive nonvested shares Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount 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. Amortized Cost Available-for-sale Securities, Amortized Cost Basis [Abstract] Due in 1 year Available-for-sale Securities, Debt Maturities, Next Rolling Twelve Months, Amortized Cost Basis Due after 1 but within 5 years Available-for-sale Securities, Debt Maturities, Rolling Year Two Through Five, Amortized Cost Basis Due after 5 but within 10 years Available-for-sale Securities, Debt Maturities, Rolling Year Six Through Ten, Amortized Cost Basis Due after 10 years Available-for-sale Securities, Debt Maturities, Rolling after Year Ten, Amortized Cost Basis Subtotal Available-for-sale Securities, Debt Maturities, Single Maturity Date, Amortized Cost Basis Total amortized investment Fair Value Due in 1 year Available-for-sale Securities, Debt Maturities, Next Rolling Twelve Months, Fair Value Due after 1 but within 5 years Available-for-sale Securities, Debt Maturities, Rolling Year Two Through Five, Fair Value Due after 5 but within 10 years Available-for-sale Securities, Debt Maturities, Rolling Year Six Through Ten, Fair Value Due after 10 years Available-for-sale Securities, Debt Maturities, Rolling after Year Ten, Fair Value Subtotal Available-for-sale Securities, Debt Maturities, Single Maturity Date Schedule of future minimum lease payments of all non-cancelable operating leases Schedule of Future Minimum Rental Payments for Operating Leases [Table Text Block] Net purchases of T&L Bonds T&L Bonds held as of end of year Subsequent Event Type [Axis] Subsequent Event Type [Axis] Subsequent Event Type [Domain] Subsequent Event Type [Domain] Subsequent event Subsequent Event [Member] Equity-Based Arrangements, Individual Contracts, Type of Deferred Compensation [Axis] Equity-Based Arrangements, Individual Contracts, Type of Deferred Compensation [Axis] Equity-Based Arrangements, Individual Contracts, Type of Deferred Compensation [Domain] Equity-Based Arrangements, Individual Contracts, Type of Deferred Compensation [Domain] 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. Title of Individual [Axis] Title of Individual [Axis] Relationship to Entity [Domain] Relationship to Entity [Domain] Certain 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. Employee Employee [Member] Employee [Member] Director Director [Member] Certain Employees Certain Employees [Member] Certain Employees [Member] Vesting [Axis] Vesting [Axis] Vesting [Domain] Vesting [Domain] First Anniversary Of Completion Of Performance Period Vesting First Anniversary Of Completion Of Performance Period Vesting [Member] Represents information pertaining to the vesting of equity-based compensation on the one-year anniversary of the completion of the performance period. Vesting period one Share-based Compensation Award, Tranche One [Member] Vesting period two Share-based Compensation Award, Tranche Two [Member] Vesting period three Share-based Compensation Award, Tranche Three [Member] Vesting period four Share-based Compensation Award, Tranche Four [Member] Share-based Compensation Award, Tranche Four [Member] Plan Name [Axis] Plan Name [Axis] Plan Name [Domain] Plan Name [Domain] 2013 Plan Essent Group Limited2013 Long Term Incentive Plan [Member] Represents the Essent Group Limited 2013 Long-term Incentive Plan (2013 Plan). Vesting Based On Performance Vesting Based On Performance [Member] Represents a share based compensation award with vesting based on achievement of performance conditions. Shares authorized (in shares) Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Authorized Nonvested shares outstanding (in shares) Number of share available for future grant (in shares) Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Available for Grant Vesting (as a percent) Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Rights, Percentage 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. Vesting period Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Period 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 Total unrecognized compensation expense Employee Service Share-based Compensation, Nonvested Awards, Compensation Not yet Recognized, Share-based Awards Other than Options Expected weighted average period for recognition of expense Employee Service Share-based Compensation, Nonvested Awards, Compensation Cost Not yet Recognized, Period for Recognition Shares tendered by employees to pay employee withholding taxes (in shares) Shares Paid for Tax Withholding for Share Based Compensation Statutory Accounting Practices [Table] Statutory Accounting Practices [Table] Essent Guaranty And Essent PA Essent Guaranty And Essent PA [Member] Essent Guaranty And Essent PA [Member] Dividends Restrictions Statutory Accounting Practices [Line Items] Award Date [Axis] Award Date [Axis] Award Date [Domain] Award Date [Domain] 2017 Performance-Based Grants Two Thousand Seventeen Performance-Based Grants [Member] Two Thousand Seventeen Performance-Based Grants [Member] 2016 Performance-Based Grants Two Thousand Sixteen Performance-Based Grants [Member] Two Thousand Sixteen Performance-Based Grants [Member] 2013, 2014 and 2015 Performance-Based Grants Two Thousand Thirteen, Fourteen and Fifteen [Member] Two Thousand Thirteen, Fourteen and Fifteen [Member] 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] 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] Compounded Annual Book Value Per Share Growth 18 % Compounded Annual Book Value Per Share Growth Achieved 18 Percent [Member] Compounded Annual Book Value Per Share Growth Achieved 18 Percent [Member] Compounded Annual Book Value Per Share Growth 19 % Compounded Annual Book Value Per Share Growth Achieved 19 Percent [Member] Compounded Annual Book Value Per Share Growth Achieved 19 Percent [Member] 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. 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. 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. Compounded Annual Book Value Per Share Growth 11% Compounded Annual Book Value Per Share Growth Achieved11 Percent [Member] Represents information pertaining to 11% compounded annual book value per share growth achieved. Compounded Annual Book Value Per Share Growth 12% Compounded Annual Book Value Per Share Growth Achieved12 Percent [Member] Represents information pertaining to 12% compounded annual book value per share growth achieved. 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. Nonvested Common Shares Earned Rollforward of accumulated other comprehensive income (loss) Schedule of Accumulated Other Comprehensive Income (Loss) [Table Text Block] Loss Contingencies [Table] Loss Contingencies [Table] Loss Contingency Nature [Axis] Loss Contingency Nature [Axis] Loss Contingency, Nature [Domain] Loss Contingency, Nature [Domain] Indemnifications related to contract underwriting services Indemnification Agreement [Member] Loss Contingencies [Line Items] Loss Contingencies [Line Items] Amount paid for remedies Loss Contingency Accrual, Payments Related Party Transactions [Abstract] Related Party Transactions Related Party Transactions Disclosure [Text Block] Summary of Investments, Other than Investments in Related Parties [Abstract] Schedule I-Summary of Investments-Other Than Investments in Related Parties Summary of Investments, Other than Investments in Related Parties [Text Block] Property, Plant and Equipment [Table] Property, Plant and Equipment [Table] Property, Plant and Equipment, Type [Axis] Property, Plant and Equipment, Type [Axis] Property, Plant and Equipment, Type [Domain] Property, Plant and Equipment, Type [Domain] Furniture and fixtures Furniture and Fixtures [Member] Equipment, computer hardware and purchased software Equipment, Computer Hardware And Purchased Software [Member] Equipment, Computer Hardware And Purchased Software [Member] Office equipment Office Equipment [Member] Computer hardware Computer Equipment [Member] Purchased software Purchased Software [Member] Purchased software applications for long-term internal use. Costs of internal-use software Software Development [Member] Leasehold improvements Leasehold Improvements [Member] Long-Lived Assets Property, Plant and Equipment [Line Items] Estimated useful lives (in years) Property, Plant and Equipment, Useful Life Cost Property, Plant and Equipment, Gross Accumulated Depreciation/ Amortization Accumulated Depreciation, Depletion and Amortization, Property, Plant, and Equipment Goldman Sachs Goldman Sachs Group Inc [Member] Represents information pertaining to The Goldman Sachs Group, Inc. Goldman Sachs Asset Management L.P. Goldman Sachs Asset Management Limited Partnership [Member] Represents Goldman Sachs Asset Management, L.P., a subsidiary of The Goldman Sachs Group, Inc. (Goldman Sachs), a shareholder of the reporting entity. Investment, Name [Axis] Investment, Name [Axis] Investment, Name [Domain] Investment, Name [Domain] Essent Group Essent Group Limited [Member] Represents Essent Group Ltd., a Bermuda-based holding company. Investor Investor [Member] Investment advisory agreement Investment Advisory Agreement [Member] Represents an agreement with an outside party to perform investment advisory services to the entity. Related Party Transactions Percentage of outstanding shares held by investor (less than after IPO) Percentage of Outstanding Shares Held by Investor Represents the percentage of outstanding shares held by investor. Expense incurred Related Party Transaction, Expenses from Transactions with Related Party Debt issuance costs, gross Debt Issuance Costs, Gross Commitment fees and interest incurred Debt Related Commitment Fees and Debt Issuance Costs Statutory net income Statutory Accounting Practices, Statutory Net Income Amount 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. 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. Increase in contingency reserve Statutory Accounting Practices, Increase (Decrease) in Contingency Reserve Represents the amount of increase (decrease) in contingency reserve. Statutory capital and surplus Statutory Accounting Practices, Statutory Capital and Surplus, Balance Authorized share capital (in shares) Common Stock, Shares Authorized Number of votes per share Common Stock Number of Votes Per Share Represents the number of votes for each share of common stock held. Shareholder ownership threshold for voting rights (as a percent) Shareholder Voting Rights Ownership Percentage Threshold Shareholder Voting Rights Ownership Percentage Threshold Maximum number of votes per share for certain shareholders under 9.5% shareholder provision Maximum Number Of Votes Per Share Certain Shareholders Under 9.5 Percent Shareholder Provision Maximum Number Of Votes Per Share Certain Shareholders Under 9.5 Percent Shareholder Provision 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 Common Shares, issued (in shares) Common Stock, Shares, Issued Share price (in dollars per share) Sale of Stock, Price Per Share Net proceeds from sale of stock Schedule of investments available for sale Schedule of Available-for-sale Securities Reconciliation [Table Text Block] Schedule of amortized cost and fair value of investments available for sale by contractual maturity Investments Classified by Contractual Maturity Date [Table Text Block] Schedule of realized gross gains and losses on sale of investments available for sale Schedule of Realized Gain (Loss) [Table Text Block] Schedule of fair value of investments in an unrealized loss position and related unrealized losses Schedule of Unrealized Loss on Investments [Table Text Block] Schedule of net investment income Investment Income [Table Text Block] Earnings per Share (EPS) Earnings Per Share [Text Block] New Accounting Pronouncements or Change in Accounting Principle [Table] New Accounting Pronouncements or Change in Accounting Principle [Table] Adjustments for New Accounting Pronouncements [Axis] Adjustments for New Accounting Pronouncements [Axis] Type of Adoption [Domain] Type of Adoption [Domain] Accounting Standard Update 2018-02 Accounting Standard Update 2018-02 [Member] Accounting Standard Update 2018-02 [Member] New Accounting Pronouncements or Change in Accounting Principle [Line Items] New Accounting Pronouncements or Change in Accounting Principle [Line Items] Receivables [Abstract] Accounts Receivable Loans, Notes, Trade and Other Receivables Disclosure [Text Block] Schedule of Accounts, Notes, Loans and Financing Receivable [Table] Schedule of Accounts, Notes, Loans and Financing Receivable [Table] Receivable Type [Axis] Receivable Type [Axis] Receivable [Domain] Receivable [Domain] Premiums receivable Premiums Receivable [Member] Accounts receivable Accounts, Notes, Loans and Financing Receivable [Line Items] Accounts Receivable Accounts Receivable, Net [Abstract] Premiums receivable Premiums Receivable, Gross Other receivables Other Receivables Total accounts receivable Accounts Receivable, Gross Less: Allowance for doubtful accounts Allowance for Doubtful Accounts Receivable Accounts receivable, net Threshold period unpaid for write-off of mortgage insurance premiums Threshold Period Past Due for Write-off of Trade Accounts Receivable Provision for doubtful accounts Provision for Doubtful Accounts Operating Loss Carryforwards [Table] Operating Loss Carryforwards [Table] Income Tax Authority [Axis] Income Tax Authority [Axis] Income Tax Authority [Domain] Income Tax Authority [Domain] United States Ireland Tax Treaty Benefits Availed United States Ireland Tax Treaty Benefits Availed [Member] Represents information assuming benefits under the U.S./Ireland tax treaty are availed. Absent Benefits Of United States Ireland Tax Treaty Absent Benefits Of United States Ireland Tax Treaty [Member] Represents information absent benefits under the U.S./Ireland tax treaty. Essent Irish Intermediate Essent Irish Intermediate Holdings Limited [Member] Represents Essent Irish Intermediate Holdings Limited (Essent Irish Intermediate), a wholly-owned subsidiary of the reporting entity and direct parent of Essent Holdings, Inc. (Essent Holdings). Geographical [Axis] Geographical [Axis] Geographical [Domain] Geographical [Domain] U.S. UNITED STATES Essent Holdings Essent Us Holdings Inc [Member] Represents Essent US Holdings, Inc. (Essent Holdings), an indirect wholly-owned subsidiary of the reporting entity through which, by way of its wholly-owned subsidiaries, the reporting entity's primary operations are conducted. Operating Loss Carryforwards [Line Items] Operating Loss Carryforwards [Line Items] Withholding tax rate on dividends paid (as a percent) Foreign Earnings Repatriated, Withholding Tax Rate, Percent This element represents the withholding tax percentage applied to the amount of foreign earnings repatriated from subsidiaries outside the country of domicile. Withholding taxes accrued with respect to un-remitted earnings Deferred Tax Liabilities, Undistributed Foreign Earnings Taxes provided on un-remitted earnings Deferred Tax Liabilities, Undistributed Domestic Earnings Amount of deferred tax liability attributable to taxable temporary differences from undistributed earnings of subsidiaries and other recognized entities within the country of domicile of the entity. Cumulative amount of earnings that would be subject to withholding tax, if distributed outside of the U.S. Undistributed Earnings of Domestic Subsidiaries Associated withholding tax liability on cumulative amount of earnings that would be subject to withholding tax, if distributed outside of the U.S. Deferred Tax Liability Not Recognized, Amount of Unrecognized Deferred Tax Liability, Undistributed Earnings of Domestic Subsidiaries Unrecognized tax benefits Unrecognized Tax Benefits Liability for uncertain tax positions Liability for Uncertainty in Income Taxes, Noncurrent Investment Secondary Categorization [Axis] Investment Secondary Categorization [Axis] Investments by Secondary Categorization [Domain] Investments by Secondary Categorization [Domain] 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. 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. 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. 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. Special tax bonds Special Tax Bond [Member] Special Tax Bond [Member] Investment Sector [Axis] Investment Sector [Axis] Investment Sector [Domain] Investment Sector [Domain] Financial Financial Sector [Member] Financial Sector [Member] Consumer, non-cyclical Consumer, Non-cyclical Sector [Member] Consumer, Non-cyclical Sector [Member] Energy Energy Sector [Member] Energy Sector [Member] Communications Communications Sector [Member] Communications Sector [Member] Industrial Industrial Sector [Member] Industrial Sector [Member] Consumer, cyclical Consumer, Cyclical Sector [Member] Consumer, Cyclical Sector [Member] Utilities Utilities Sector [Member] Utilities Sector [Member] Technology Technology Debt Sector [Member] Technology Debt Sector [Member] Basic materials Basic Materials Sector [Member] Basic Materials Sector [Member] Percentage of debt securities Investment Owned, Percent of Net Assets Accounting Standards Update 2016-09 Accounting Standards Update 2016-09 [Member] Cumulative effect of new accounting principle in period of adoption Summary of Significant Accounting Policies Significant Accounting Policies [Text Block] Debt Obligations Debt Disclosure [Text Block] Rent expense Operating Leases, Rent Expense, Net Future minimum lease payments of all non-cancelable operating leases Operating Leases, Future Minimum Payments Due, Fiscal Year Maturity [Abstract] 2018 Operating Leases, Future Minimum Payments Due, Next Twelve Months 2019 Operating Leases, Future Minimum Payments, Due in Two Years 2020 Operating Leases, Future Minimum Payments, Due in Three Years 2021 Operating Leases, Future Minimum Payments, Due in Four Years 2022 Operating Leases, Future Minimum Payments, Due in Five Years 2023 and thereafter Operating Leases, Future Minimum Payments, Due Thereafter Total minimum payments required Operating Leases, Future Minimum Payments Due Minimum sublease rental income, due in 2018 Operating Leases, Future Minimum Payments Due, Future Minimum Sublease Rentals Statutory Accounting Statutory Accounting Disclosure [Text Block] Represents the entire disclosure pertaining to the statutory accounting. Nature of Operations and Basis of Presentation Organization, Consolidation and Presentation of Financial Statements Disclosure [Text Block] Common stock, issuance cost Adjustments to Additional Paid in Capital, Stock Issued, Issuance Costs Reconciliation of the beginning and ending reserve balances for losses and loss adjustment expenses (LAE) Liability for Unpaid Claims and Claims Adjustment Expense, Period Increase (Decrease) [Abstract] Reserve for losses and LAE at beginning of year Less: Reinsurance recoverables Reinsurance Recoverable for Unpaid Claims and Claims Adjustments Net reserve for losses and LAE at beginning of year Add provision for losses and LAE, net of reinsurance, occurring in: Liability for Unpaid Claims and Claims Adjustment Expense, Incurred Claims [Abstract] Current year Current Year Claims and Claims Adjustment Expense Prior years Net incurred losses during the current year Deduct payments for losses and LAE, net of reinsurance, occurring in: Liability for Unpaid Claims and Claims Adjustment Expense, Claims Paid [Abstract] Current year Liability for Unpaid Claims and Claims Adjustment Expense, Claims Paid, Current Year Prior years Net loss and LAE payments during the current year Liability for Unpaid Claims and Claims Adjustment Expense, Claims Paid Net reserve for losses and LAE at end of year Plus: Reinsurance recoverables Reserve for losses and LAE at end of year Loans in default at end of year Number of Loans in Default Represents the number of loans in default. Deferred Policy Acquisition Costs [Table] Deferred Policy Acquisition Costs [Table] Deferred Policy Acquisition Costs [Table] Other underwriting and operating expenses Other Underwriting And Operating Expenses [Member] Primary financial statement caption encompassing other underwriting and operating expenses. Deferred Policy Acquisition Costs [Line Items] Deferred Policy Acquisition Costs [Line Items] [Line Items] for Deferred Policy Acquisition Costs [Table] Deferred Policy Acquisition Costs Deferred Policy Acquisition Costs Disclosures [Abstract] Policy acquisition costs deferred Deferred Policy Acquisition Costs, Additions Amortization of deferred policy acquisition costs Deferred Policy Acquisition Costs, Amortization Expense Use of Estimates Use of Estimates, Policy [Policy Text Block] Investments Available for Sale Marketable Securities, Available-for-sale Securities, Policy [Policy Text Block] Long-Lived Assets Property, Plant and Equipment, Policy [Policy Text Block] Deferred Policy Acquisition Costs Deferred Policy Acquisition Costs, Policy [Policy Text Block] Insurance Premium Revenue Recognition Insurance Premiums Revenue Recognition, Policy [Policy Text Block] Reserve for Losses and Loss Adjustment Expenses Unpaid Policy Claims and Claims Adjustment Expense, Policy [Policy Text Block] Premium Deficiency Reserve Anticipated Investment Income as Component of Premium Deficiency on Short Duration Contracts, Policy [Policy Text Block] Derivative Instruments Derivatives, Policy [Policy Text Block] Stock-Based Compensation Share-based Compensation, Option and Incentive Plans Policy [Policy Text Block] Income Taxes Income Tax, Policy [Policy Text Block] Earnings per Share Earnings Per Share, Policy [Policy Text Block] Recently Issued Accounting Standards New Accounting Pronouncements, Policy [Policy Text Block] Net premiums earned Other revenues Revenues Other than Premiums Earned, Net All revenues other than the net revenues from premiums earned. Provision for losses and LAE Policyholder Benefits and Claims Incurred, Net Income before income taxes Basic earnings per Common Share (in dollars per share) Diluted earnings per Common Share (in dollars per share) Diluted weighted average Common Shares outstanding (in shares) Investments available for sale Amortized cost Property and equipment Property, Plant and Equipment, Net [Abstract] Accumulated depreciation Credit Facility Borrowings Subordinated Borrowings [Abstract] Unamortized deferred costs Common Shares, par value (in dollars per share) Common Stock, Par or Stated Value Per Share Common Shares, authorized (in shares) Common Shares, outstanding (in shares) Common Stock, Shares, Outstanding Summary of Investments, Other than Investments in Related Parties [Table] Summary of Investments, Other than Investments in Related Parties [Table] United States Government and government agencies and authorities US Treasury and Government [Member] States, municipalities and political subdivisions US States and Political Subdivisions Debt Securities [Member] All other corporate bonds Other Corporate Bonds [Member] Investments-Other Than Investments in Related Parties Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items] Amortized Cost Fair Value Amount at which shown in the Balance Sheet Summary of Investments, Other than Investments in Related Parties, Carrying Amount Income Tax Authority, Name [Axis] Income Tax Authority, Name [Axis] Income Tax Authority, Name [Domain] Income Tax Authority, Name [Domain] Office of the Tax Commissioner, Bermuda Office of the Tax Commissioner, Bermuda [Member] Internal Revenue Service (IRS) Internal Revenue Service (IRS) [Member] Bermuda Foreign Tax Authority [Member] U.S. Domestic Tax Authority [Member] Bermuda BERMUDA Statutory rate (as a percent) Effective Income Tax Rate Reconciliation, at Federal Statutory Income Tax Rate, Percent Tax Cuts and Jobs Act of 2017 tax expense (benefit) Tax Cuts And Jobs Act Of 2017, Income Tax Expense (Benefit) Tax Cuts And Jobs Act Of 2017, Income Tax Expense (Benefit) Components of income tax expense Components of Income Tax Expense (Benefit), Continuing Operations [Abstract] Current Current Income Tax Expense (Benefit) Deferred Deferred Income Tax Expense (Benefit) Before The Effect Of Tax Act Of 2017 Deferred Income Tax Expense (Benefit) Before The Effect Of Tax Act Of 2017 Remeasurement of net deferred tax liability for enacted changes in tax law Total income tax expense Effective Income Tax Rate Reconciliation, Amount Effective Income Tax Rate Reconciliation, Amount [Abstract] 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. Change in valuation of net deferred tax liability Effective Income Tax Rate Reconciliation, Tax Cuts And Jobs Act Of 2017, Amount Effective Income Tax Rate Reconciliation, Tax Cuts and Jobs Act of 2017, Amount Excess tax benefits from stock-based compensation Effective Income Tax Rate Reconciliation, Share-based Compensation, Excess Tax Benefit, Amount Effective Income Tax Rate Reconciliation, Share-based Compensation, Excess Tax Benefit, Amount 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. 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. 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. % of pretax income Effective Income Tax Rate Reconciliation, Percent [Abstract] Tax provision (benefit) at weighted average statutory rates (as a percent) Effective Income Tax Rate Reconciliation at Weighted Average Statutory Income Tax Rate Percentage of weighted average statutory tax rate applicable to pretax income (loss). Change in valuation of net deferred tax liability (as a percent) Effective Income Tax Rate Reconciliation, Tax Cuts And Jobs Act Of 2017, Percent Effective Income Tax Rate Reconciliation, Tax Cuts And Jobs Act Of 2017, Percent Excess tax benefits from stock-based compensation (as a percent) Effective Income Tax Rate Reconciliation, Share-based Compensation, Excess Tax Benefit, Percent Effective Income Tax Rate Reconciliation, Share-based Compensation, Excess Tax Benefit, Percent Tax exempt interest, net of proration (as a percent) 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. Non-deductible expenses (as a percent) 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. Other (as a percent) 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. Total income tax expense (as a percent) Effective Income Tax Rate Reconciliation, Percent Schedule of accounts receivable Schedule of Accounts, Notes, Loans and Financing Receivable [Table Text Block] Document and Entity Information Entity Registrant Name Entity Registrant Name Entity Central Index Key Entity Central Index Key Document Type Document Type Document Period End Date Document Period End Date Amendment Flag Amendment Flag Current Fiscal Year End Date Current Fiscal Year End Date Entity Well-known Seasoned Issuer Entity Well-known Seasoned Issuer Entity Voluntary Filers Entity Voluntary Filers Entity Current Reporting Status Entity Current Reporting Status Entity Filer Category Entity Filer Category Entity Public Float Entity Public Float Entity Common Stock, Shares Outstanding Entity Common Stock, Shares Outstanding Document Fiscal Year Focus Document Fiscal Year Focus Document Fiscal Period Focus Document Fiscal Period Focus Income Taxes Income Tax Disclosure [Text Block]