Segment Reporting [Abstract] Schedule of Segment Reporting Information, by Segment [Table] Schedule of Segment Reporting Information, by Segment [Table] Segments [Axis] Segments [Axis] Segments [Domain] Segments [Domain] Excess and Surplus Lines Excess And Surplus Lines [Member] Represents information regarding excess and surplus lines segment. Specialty Admitted Insurance Specialty Admitted Insurance [Member] Represents information regarding specialty admitted insurance. Casualty Reinsurance Casualty Reinsurance [Member] Represents information regarding casualty reinsurance. Corporate and other segment Corporate and Other [Member] Segment Reporting Information [Line Items] Segment Reporting Information [Line Items] Underwriting profit of operating segments Underwriting Profit Loss Of Operating Segments This element represents amount of underwriting Profit (loss) of operating segments. Other operating expenses Other Operating Expenses Of Corporate And Other Segment Represents Other operating expenses of the Corporate and Other segment. Underwriting profit Underwriting Profit Loss Represents the amount related to underwriting profit (loss) during the period. Net investment income Net Investment Income Net realized investment (losses) gains Realized Investment Gains (Losses) Other income Other Income And Expenses Represents other income and expenses. Other expenses Other Expenses Interest expense Interest Expense Amortization of intangible assets Amortization of Intangible Assets Income before income taxes Income (Loss) from Continuing Operations before Income Taxes, Noncontrolling Interest Stockholders' Equity Note [Abstract] Capital Stock Stockholders' Equity Note Disclosure [Text Block] Fair Value Disclosures [Abstract] Fair Value, by Balance Sheet Grouping [Table] Fair Value, by Balance Sheet Grouping [Table] Measurement Basis [Axis] Measurement Basis [Axis] Fair Value Measurement [Domain] Fair Value Measurement [Domain] Portion at Fair Value Measurement Portion at Fair Value Measurement [Member] Carrying Value Reported Value Measurement [Member] Fair Value Estimate of Fair Value Measurement [Member] Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] Assets Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract] Fixed maturity securities, available-for-sale Debt Securities, Available-for-sale Equity securities, at fair value (cost: 2018 – $77,152; 2017 – $75,318) Equity Securities, FV-NI Fixed maturity securities, trading Debt Securities, Trading, and Equity Securities, FV-NI Bank loan participations held-for-investment, at amortized cost, net of allowance Loans Receivable, Net Cash and cash equivalents Cash and Cash Equivalents, at Carrying Value Short-term investments Short-term Investments Other invested assets – notes receivable Notes Receivable Represents carrying value of notes receivable as on reporting date. Liabilities Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract] Senior debt Long-term Debt Junior subordinated debt Junior Subordinated Notes 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 and NAV [Axis] Fair Value Hierarchy and NAV [Axis] Fair Value Hierarchy and NAV [Domain] Fair Value Hierarchy and NAV [Domain] Quoted Prices in Active Markets for Identical Assets Level 1 Fair Value, Inputs, Level 1 [Member] Significant Other Observable Inputs Level 2 Fair Value, Inputs, Level 2 [Member] Significant Unobservable Inputs Level 3 Fair Value, Inputs, Level 3 [Member] Financial Instrument [Axis] Financial Instrument [Axis] Financial Instruments [Domain] Financial Instruments [Domain] Fixed maturity securities: Debt Securities [Member] State and municipal US States and Political Subdivisions Debt Securities [Member] Residential mortgage-backed Residential Mortgage Backed Securities [Member] Corporate Corporate Debt Securities [Member] Commercial mortgage and asset-backed Commercial Mortgage Backed Securities [Member] Obligations of U.S. government corporations and agencies US Government Corporations and Agencies Securities [Member] U.S. Treasury securities and obligations guaranteed by the U.S. government US Treasury and Government [Member] Redeemable preferred stock Redeemable Preferred Stock [Member] Equity securities Equity Securities [Member] Preferred stock Preferred Stock [Member] Common stock Common Stock [Member] Fixed maturity securities, available-for-sale: Debt Securities [Abstract] Available-for-sale, at fair value (amortized cost: 2018 – $1,199,409; 2017 – $1,008,662) Equity securities: Equity Securities, FV-NI and without Readily Determinable Fair Value [Abstract] Equity securities Trading securities: Debt Securities, Current [Abstract] Fixed maturity securities Debt Securities, Trading Liability for Claims and Claims Adjustment Expense [Abstract] Short-duration Insurance Contracts, Claims Development [Table] Short-duration Insurance Contracts, Claims Development [Table] Subsegments [Axis] Subsegments [Axis] Subsegments [Domain] Subsegments [Domain] Commercial Auto Commercial Auto [Member] Commercial Auto [Member] Excluding Commercial Auto Excluding Commercial Auto [Member] Excluding Commercial Auto [Member] Fronting and Programs Fronting and Programs [Member] Represents information of Fronting and Programs. Individual Risk Workers' Compensation Individual Risk Workers Compensation [Member] Represents information about individual risk workers compensation. 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] Accident year 2009 Short-duration Insurance Contracts, Accident Year 2009 [Member] Accident year 2010 Short-duration Insurance Contracts, Accident Year 2010 [Member] Accident year 2011 Short-duration Insurance Contracts, Accident Year 2011 [Member] Accident year 2012 Short-duration Insurance Contracts, Accident Year 2012 [Member] Accident year 2013 Short-duration Insurance Contracts, Accident Year 2013 [Member] Accident year 2014 Short-duration Insurance Contracts, Accident Year 2014 [Member] Accident year 2015 Short-duration Insurance Contracts, Accident Year 2015 [Member] Accident year 2016 Short-duration Insurance Contracts, Accident Year 2016 [Member] Accident year 2017 Short-duration Insurance Contracts, Accident Year 2017 [Member] Accident year 2018 Short-duration Insurance Contracts, Accident Year 2018 [Member] Claims Development [Line Items] Claims Development [Line Items] Short-duration insurance contracts, incurred claims and allocated claim adjustment expense, net Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net Cumulative paid losses and loss adjustment expenses, net of reinsurance Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net All outstanding losses and loss adjustment expenses prior to 2009, net of reinsurance Short-duration Insurance Contracts, Liability for Unpaid Claims and Allocated Claim Adjustment Expense, Net, Not Separately Presented Total outstanding losses and loss adjustment expenses, net of reinsurance Short-duration Insurance Contracts, Liability for Unpaid Claims and Allocated Claim Adjustment Expense, Net Statement of Financial Position [Abstract] Assets Assets [Abstract] Invested assets: Investments [Abstract] Fixed maturity securities: Trading, at fair value (amortized cost: 2018 – $0; 2017 – $3,801) Other invested assets Other Investments Total invested assets Investments Accrued investment income Accrued Investment Income Receivable Premiums receivable and agents’ balances, net Premiums and Other Receivables, Net Reinsurance recoverable on unpaid losses Reinsurance Recoverable for Unpaid Claims and Claims Adjustments Reinsurance recoverable on paid losses Reinsurance Recoverable for Paid Claims and Claims Adjustments Prepaid reinsurance premiums Prepaid Reinsurance Premiums Deferred policy acquisition costs Deferred Policy Acquisition Costs Intangible assets, net Intangible Assets, Net (Excluding Goodwill) Goodwill Goodwill Deferred tax assets, net Deferred Tax Assets, Net of Valuation Allowance Income taxes receivable Income Taxes Receivable Other assets Other Assets Total assets Assets Liabilities and shareholders’ equity Liabilities and Equity [Abstract] Liabilities: Liabilities [Abstract] Reserve for losses and loss adjustment expenses Liability for Claims and Claims Adjustment Expense Unearned premiums Unearned Premiums Payables to reinsurers Reinsurance Payable Junior subordinated debt Junior Subordinated Debenture Owed to Unconsolidated Subsidiary Trust Accrued expenses Accrued Liabilities Deferred tax liabilities, net Deferred Income Tax Liabilities, Net Income taxes payable Taxes Payable Other liabilities Other Liabilities Total liabilities Liabilities Commitments and contingent liabilities Commitments and Contingencies Shareholders’ equity: Stockholders' Equity Attributable to Parent [Abstract] Common Shares – $0.0002 par value; 200,000,000 shares authorized. 2018 and 2017: 29,988,460 and 29,696,682 shares issued and outstanding, respectively Common Stock, Value, Issued Preferred Shares – 2018 and 2017: $0.00125 par value; 20,000,000 shares authorized; no shares issued and outstanding Preferred Stock, Value, Issued Additional paid-in capital Additional Paid in Capital Retained earnings Retained Earnings (Accumulated Deficit) Accumulated other comprehensive (loss) income Accumulated Other Comprehensive Income (Loss), Net of Tax Total shareholders’ equity Stockholders' Equity Attributable to Parent Total liabilities and shareholders’ equity Liabilities and Equity Statutory Accounting Practices, Statutory Amount Available for Dividend Payments [Abstract] Statutory Accounting Practices [Table] Statutory Accounting Practices [Table] Jurisdiction [Axis] Jurisdiction [Axis] Statutory Accounting Practices, Jurisdiction [Domain] Statutory Accounting Practices, Jurisdiction [Domain] UNITED STATES UNITED STATES BERMUDA BERMUDA Legal Entity [Axis] Legal Entity [Axis] Entity [Domain] Entity [Domain] JRG Re Jrg Reinsurance Company Ltd [Member] Represents reinsurance subsidiary of the entity. Statutory Accounting Practices [Line Items] Statutory Accounting Practices [Line Items] Dividend limitations percentage of statutory surplus Dividend Limitations Percentage Of Statutory Surplus Represents dividend limitations percentage of statutory surplus. Maximum amount of dividends available without regulatory approval Statutory Accounting Practices, Statutory Amount Available for Dividend Payments without Regulatory Approval Percentage of dividend withholding tax for distributions Percentage Of Dividend Withholding Tax For Distributions Represents the percentage of dividend withholding tax for distributions. Percentage of dividend distribution tax Percentage Of Dividend Distribution Tax Represents percentage of dividend distribution tax. Maximum amount of dividends and return of capital available Statutory Accounting Practices, Statutory Amount Available for Dividend Payments Broker one Broker One [Member] Name of party. Broker two Broker Two [Member] Name of party. Insured one Insured One [Member] Represents information of insured one. Agency one Agency One [Member] Name of party. Unaffiliated ceding company one Unaffiliated Ceding Company One [Member] Name of party. Unaffiliated ceding company two Unaffiliated Ceding Company Two [Member] Name of party. Unaffiliated ceding company three Unaffiliated Ceding Company Three [Member] Unaffiliated Ceding Company Three [Member] Number of brokers Number of Brokers Number of Brokers Number of reportable segments Number of Reportable Segments Fee income Fee Income Represents amount of fee income . Number of underwriting divisions Number Of Underwriting Divisions Represents number of underwriting divisions. Gross written premiums Premiums Written, Gross Consolidated gross written premiums percentage Consolidated Gross Written Premiums Percentage Represents consolidated gross written premiums percentage. Gross written premiums percentage Gross Written Premiums Percentage Represents gross written premiums percentage. Number of unaffiliated ceding companies Number of Unaffiliated Ceding Companies Number of Unaffiliated Ceding Companies Investments, Debt and Equity Securities [Abstract] Investment Income [Table] Investment Income [Table] Bank Holding Company Bank Holding Company [Member] Represents information about Bank Holding Company. Range [Axis] Range [Axis] Range [Domain] Range [Domain] Minimum Minimum [Member] Maximum Maximum [Member] Investment in LLC Investment In Llc [Member] Represents investment in LLC`s. Bank Holding Company Investment In Bank Holding Company [Member] Represents information about Investment in bank holding company. Investment Type [Axis] Investment Type [Axis] Investments [Domain] Investments [Domain] Renewable energy LLCs Renewable Energy Llcs [Member] Name of the investment category. Renewable energy notes receivable Renewable Energy Bridge Financing Notes [Member] Name of the investment category. Limited partnerships Partnership Interest [Member] Bank holding companies Bank Holding Companies [Member] Name of the investment category. Net Investment Income [Line Items] Net Investment Income [Line Items] Total other invested assets Investment Income Investment Income, Net Ownership percentage Equity Method Investment, Ownership Percentage Distributions from equity method investments Proceeds from Equity Method Investment, Distribution Investment interest rate Investment Interest Rate Interest income Investment Income, Interest Proceeds from other investments maturities and repayments Proceeds from Other Investments Maturities and Repayments Proceeds from of Other Investments Maturities and Repayments Carrying value of investments Equity Method Investments Equity in net income of subsidiaries Income (Loss) from Equity Method Investments Commitment to investment in limited partnership Commitment to Investment In Limited Partnership Represents commitment to investment in a limited partnership. Investment in subordinated notes Payments To Acquire Private Subordinated Debt Represents payments to acquire private subordinated debt. SEC Schedule, 12-09, Valuation and Qualifying Accounts [Abstract] Valuation and Qualifying Accounts SEC Schedule, 12-09, Schedule of Valuation and Qualifying Accounts Disclosure [Text Block] Accounting Policies [Abstract] Accounting Policies Basis of Presentation and Significant Accounting Policies [Text Block] Condensed Financial Information Disclosure [Abstract] Condensed Income Statement [Table] Condensed Income Statement [Table] Consolidated Entities [Axis] Consolidated Entities [Axis] Consolidated Entities [Domain] Consolidated Entities [Domain] Parent Company Parent Company [Member] Condensed Income Statements, Captions [Line Items] Condensed Income Statements, Captions [Line Items] Revenues: Revenues [Abstract] Other income Other Income Total revenues Revenues Expenses: Operating Expenses [Abstract] Other operating expenses Other Cost and Expense, Operating Other expenses Interest expense Total expenses Operating Expenses Loss before equity in net income of subsidiaries Net income Net Income (Loss) Attributable to Parent Other comprehensive (loss) income: Other Comprehensive Income (Loss), Net of Tax [Abstract] Equity in other comprehensive (losses) earnings of subsidiaries Other Comprehensive Income (Loss), Net of Tax Total comprehensive income Comprehensive Income (Loss), Net of Tax, Attributable to Parent Income Weighted average common shares Weighted Average Number of Shares Outstanding Reconciliation [Abstract] Basic (in shares) Weighted Average Number of Shares Outstanding, Basic Common share equivalents (in shares) Weighted Average Number Diluted Shares Outstanding Adjustment Diluted (in shares) Weighted Average Number of Shares Outstanding, Diluted Earnings per share Earnings Per Share Reconciliation [Abstract] Basic earnings per share (in dollars per share) Earnings Per Share, Basic Common share equivalents (in dollars per share) Common Share Equivalents Earnings Per Share Represents amount of earnings per share of common share equivalents. Diluted earnings per share (in dollars per share) Earnings Per Share, Diluted SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Abstract] Summary of Investments - Other than Investments in Related Parties SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Text Block] SEC Schedule, 12-16, Insurance Companies, Supplementary Insurance Information [Abstract] Supplementary Insurance Information SEC Schedule, 12-16, Insurance Companies, Supplementary Insurance Information, Disclosure [Text Block] Disclosure of Compensation Related Costs, Share-based Payments [Abstract] 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 [Axis] Award Type [Axis] Equity Award [Domain] Equity Award [Domain] Options Employee Stock Option [Member] Share-based Compensation Arrangement by Share-based Payment Award [Line Items] Share-based Compensation Arrangement by Share-based Payment Award [Line Items] Shares Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding [Roll Forward] Beginning of year (in shares) Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Number Granted (in shares) Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Gross Exercised (in shares) Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercises in Period Forfeited (in shares) Share-based Compensation Arrangement by Share-based Payment Award, Options, Forfeitures in Period End of year (in shares) Exercisable, end of year (in shares) Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercisable, Number Weighted- Average Exercise Price Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Exercise Price [Abstract] Beginning of year (in dollars per share) Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Exercise Price Granted (in dollars per share) Share-based Compensation Arrangements by Share-based Payment Award, Options, Grants in Period, Weighted Average Exercise Price Exercised (in dollars per share) Share-based Compensation Arrangements by Share-based Payment Award, Options, Exercises in Period, Weighted Average Exercise Price Forfeited (in dollars per share) Share-based Compensation Arrangements by Share-based Payment Award, Options, Forfeitures in Period, Weighted Average Exercise Price End of year (in dollars per share) Exercisable, end of year Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercisable, Weighted Average Exercise Price Document And Entity Information [Abstract] Entity Registrant Name Entity Registrant Name Entity Central Index Key Entity Central Index Key Trading Symbol Trading Symbol Entity Current Reporting Status Entity Current Reporting Status Entity Voluntary Filers Entity Voluntary Filers Current Fiscal Year End Date Current Fiscal Year End Date Entity Filer Category Entity Filer Category Entity Emerging Growth Company Entity Emerging Growth Company Entity Small Business Entity Small Business Entity Shell Company Entity Shell Company Entity Well-known Seasoned Issuer Entity Well-known Seasoned Issuer Entity Common Stock, Shares Outstanding Entity Common Stock, Shares Outstanding Entity Public Float Entity Public Float Document Type Document Type Document Period End Date Document Period End Date Amendment Flag Amendment Flag Document Fiscal Period Focus Document Fiscal Period Focus Document Fiscal Year Focus Document Fiscal Year Focus Other Comprehensive (Loss) Income Comprehensive Income (Loss) Note [Text Block] Fair Value Measurements, Recurring and Nonrecurring [Table] Fair Value Measurements, Recurring and Nonrecurring [Table] Asset Class [Axis] Asset Class [Axis] Asset Class [Domain] Asset Class [Domain] Available-for-sale fixed maturity securities 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] Fair value of available-for-sale fixed maturity security Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Value Impaired bank loan participations held for investment Impaired Bank Loan Participations Held For Investment Represents impaired bank loan participations held for investment. Unpaid principal on bank loan participations for which external sources were unavailable to determine fair value Bank Loan Participations Unpaid Principal Balance Represents bank loan participations unpaid principal balance. Carrying value of bank loan participations for which external sources were unavailable to determine fair value Bank Loan Participations Carrying Value Represents carrying value of bank loan participations for which external sources were unavailable to determine fair value. Bank loan participations Bank Loan Obligations [Member] Other invested assets Other Long-term Investments [Member] Cash, cash equivalents, short-term investments, and other Cash and Cash Equivalents [Member] Trading (losses) gains Trading Gains (Losses) [Member] Represents unrealized holding loss before gain recognized in the income statement for investments in trading securities. Gross investment income Gross Investment Income, Operating Investment expense Investment Income, Investment Expense Net investment income Income Tax Disclosure [Abstract] Effective Income Tax Rate Reconciliation, Amount [Abstract] Effective Income Tax Rate Reconciliation, Amount [Abstract] Federal income tax expense at applicable statutory rates Effective Income Tax Rate Reconciliation at Federal Statutory Income Tax Rate, Amount Tax-exempt investment income Effective Income Tax Rate Reconciliation, Tax Exempt Income, Amount Dividends received deduction Effective Income Tax Rate Reconciliation, Deduction, Dividends, Amount Excess tax benefits on share based compensation Effective Income Tax Rate Reconciliation, Nondeductible Expense, Share-based Compensation Cost, Amount Effect of tax rate reduction on deferred tax liability Effective Income Tax Rate Reconciliation, Change in Enacted Tax Rate, Amount Other Effective Income Tax Rate Reconciliation, Other Adjustments, Amount Federal income tax expense Income Tax Reconciliation Federal Income Tax Expense Represents amount of the difference between reported income tax expense (benefit) and expected income tax expense (benefit) computed by applying the domestic federal statutory income tax rates. U.S. state income tax (benefit) expense Effective Income Tax Rate Reconciliation, State and Local Income Taxes, Amount U.S. dividend withholding tax Income Tax Reconciliation Us Dividend Withholding Tax Represents amount of the difference between reported income tax expense (benefit) and expected income tax expense (benefit) computed by applying the domestic federal statutory income tax rates to pretax income (loss) from continuing operations attributable to U.S. dividend withholding tax. Total income tax expense Income Tax Expense (Benefit) Income Statement [Abstract] Ceded written premiums Ceded Premiums Written Net written premiums Premiums Written, Net Change in net unearned premiums (Increase) Decrease in Unearned Premiums, Net Net earned premiums Premiums Earned, Net Net realized and unrealized (losses) gains on investments Gain (Loss) on Investments Losses and loss adjustment expenses Liability for Unpaid Claims and Claims Adjustment Expense, Incurred Claims Amortization of intangible assets Income tax expense (benefit): Income Tax Expense (Benefit), Continuing Operations [Abstract] Current Current Income Tax Expense (Benefit) Deferred Deferred Income Tax Expense (Benefit) Other comprehensive (losses) income: Net unrealized (losses) gains, net of taxes of $(444) in 2018, $2,707 in 2017, and $(1,723) in 2016 Per share data: Earnings Per Share, Basic and Diluted [Abstract] Dividend declared per share (in dollars per share) Common Stock, Dividends, Per Share, Declared Weighted-average common shares outstanding: Weighted Average Number of Shares Outstanding, Basic [Abstract] Schedule of cash dividends declared Dividends Declared [Table Text Block] Deferred Policy Acquisition Costs Disclosures [Abstract] Movement Analysis of Deferred Policy Acquisition Costs [Roll Forward] Movement Analysis of Deferred Policy Acquisition Costs [Roll Forward] Balance at beginning of period Commissions Deferred Policy Acquisition Costs, Additions Underwriting and other issue expenses Deferred Policy Acquisition Costs Underwriting And Other Issue Expenses Represents deferred policy acquisition costs underwriting and other issue expenses. Policy acquisition costs deferred Policy Acquisition Costs Deferred Represents amount of policy acquisition costs deferred during the period. Amortization of policy acquisition costs Deferred Policy Acquisition Costs, Amortization Expense Net change Deferred Policy Acquisition Costs, Period Increase (Decrease) Balance at end of period Available-for-sale debt securities, amortized cost (in dollars) Debt Securities, Available-for-sale, Amortized Cost Trading securities, debt, amortized cost (in dollars) Debt Securities, Trading, Amortized Cost Equity Securities, FV-NI, Cost Equity Securities, FV-NI, Cost Available-for-sale equity securities, amortized cost (in dollars) Available-for-sale Equity Securities, Amortized Cost Basis Common stock, par value (in dollars per share) Common Stock, Par or Stated Value Per Share Common stock, shares authorized Common Stock, Shares Authorized Common stock, shares issued Common Stock, Shares, Issued Common stock, shares outstanding Common Stock, Shares, Outstanding Preferred stock par value (in dollars per share) Preferred Stock, Par or Stated Value Per Share Preferred stock, shares authorized Preferred Stock, Shares Authorized Preferred stock, shares issued Preferred Stock, Shares Issued Preferred stock, shares outstanding Preferred Stock, Shares Outstanding Property, Plant and Equipment [Abstract] Property and Equipment, Net Property, Plant and Equipment Disclosure [Text Block] Share based compensation expense Allocated Share-based Compensation Expense U.S. tax benefit on share based compensation expense Employee Service Share-based Compensation, Tax Benefit from Compensation Expense Income Taxes Income Tax Disclosure [Text Block] Schedule of assets measured at fair value on a recurring basis Fair Value, Assets Measured on Recurring Basis [Table Text Block] Schedule of fair value on a recurring basis using significant unobservable inputs (Level 3) Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Table Text Block] Schedule of assets measured at fair value on a nonrecurring basis Fair Value Measurements, Nonrecurring [Table Text Block] Schedule of carrying value and fair value Fair Value, by Balance Sheet Grouping [Table Text Block] Fixed maturity securities, gross realized gains Debt Securities, Available-for-sale, Realized Gain Fixed maturity securities, gross realized losses Debt Securities, Available-for-sale, Realized Loss Fixed maturity securities Debt Securities, Available-for-sale, Realized Gain (Loss) Equity securities, gross realized gains Equity Securities, FV-NI, Realized Gain Equity securities, gross realized losses Equity Securities, FV-NI, Realized Loss Changes in fair values of equity securities Equity Securities, FV-NI, Realized Gain (Loss) Equity securities Equity Securities, FV-NI, Gain (Loss) Bank loan participations, gross realized gain Bank Loan Participations, Gross Realized Gain Represents the gross realized gains on bank loan participations. Bank loan participations, gross realized losses Bank Loan Participations, Gross Realized Loss Represents the gross realized losses on bank loan participations. Bank loan participations Bank Loan Participations, Gross Realized Gain (Loss) Bank Loan Participations, Gross Realized Gain (Loss) Short-term investments and other, gross realized gains Short Term Investments And Other Gross Realized Gains Represents the gross profit realized on the sale of short term investment and other. Short-term investments and other, gross realized losses Short Term Investments And Other Gross Realized Losses Represents the gross loss realized on the sale of short term investment and other. Short-term investments and other Short Term Investments And Other Gross Realized Gains (Losses) Short Term Investments And Other Gross Realized Gains (Losses) Realized gains and losses on investments SEC Schedule, 12-17, Insurance Companies, Reinsurance [Abstract] Reinsurance SEC Schedule, 12-17, Insurance Companies, Reinsurance [Text Block] Tax on net unrealized gains (losses) Other Comprehensive Income (Loss), Securities, Available-for-sale, Tax Fair Value Measurements Fair Value Disclosures [Text Block] Short-duration Insurance Contracts, Historical Claims Duration [Table] Short-duration Insurance Contracts, Historical Claims Duration [Table] E&S Short-duration Insurance Contracts, Historical Claims Duration [Line Items] Short-duration Insurance Contracts, Historical Claims Duration [Line Items] 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 Year 7 Short-duration Insurance Contracts, Historical Claims Duration, Year Seven Year 8 Short-duration Insurance Contracts, Historical Claims Duration, Year Eight Year 9 Short-duration Insurance Contracts, Historical Claims Duration, Year Nine Year 10 Short-duration Insurance Contracts, Historical Claims Duration, Year Ten Schedule of property and equipment, net Property, Plant and Equipment [Table Text Block] Reinsurance Disclosures [Abstract] Written premiums: Premiums Written, Net [Abstract] Direct Direct Premiums Written Assumed Assumed Premiums Written Ceded Earned premiums: Premiums Earned, Net [Abstract] Direct Direct Premiums Earned Assumed Assumed Premiums Earned Ceded Ceded Premiums Earned Losses and loss adjustment expenses: Policyholder Benefits and Claims Incurred, Net [Abstract] Direct Policyholder Benefits and Claims Incurred, Direct Assumed Policyholder Benefits and Claims Incurred, Assumed Ceded Policyholder Benefits and Claims Incurred, Ceded Net Policyholder Benefits and Claims Incurred, Net 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] Building, leased for which the Company has been deemed the owner for accounting purposes (Note 21) Building [Member] Electronic data processing hardware and software Electronic Data Processing Hardware And Software [Member] Represents information about electronic data processing hardware and software. Furniture and equipment Furniture and Fixtures [Member] Property, Plant and Equipment [Line Items] Property, Plant and Equipment [Line Items] Property and equipment, cost basis Property, Plant and Equipment, Gross Accumulated depreciation Accumulated Depreciation, Depletion and Amortization, Property, Plant, and Equipment Property and equipment, net Property, Plant and Equipment, Net Commitments and Contingencies Disclosure [Abstract] Commitments and Contingent Liabilities Commitments and Contingencies Disclosure [Text Block] Schedule of Available-for-sale Securities [Table] Schedule of Available-for-sale Securities [Table] Debt Securities, Available-for-sale [Line Items] Debt Securities, Available-for-sale [Line Items] Cost or Amortized Cost Gross Unrealized Gains Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax Gross Unrealized Losses Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax Fair Value Schedule of summary of available-for-sale investments Schedule of Available-for-sale Securities Reconciliation [Table Text Block] Schedule of summary of available-for-sale investments by contractual maturity Investments Classified by Contractual Maturity Date [Table Text Block] Schedule of gross unrealized losses and fair value for available-for-sale securities Debt Securities, Available-for-sale [Table Text Block] Schedule of major categories of the company' s net investment income Investment Income [Table Text Block] Schedule of summary of realized gains and losses Realized Gain (Loss) on Investments [Table Text Block] Schedule of available-for-sale gross unrealized gains or losses Unrealized Gain (Loss) on Investments [Table Text Block] Schedule of other invested assets Other Invested Asset [Table Text Block] Tabular disclosure of other invested assets consisting of private debt and equity investments. Subsequent Events [Abstract] Subsequent Events Subsequent Events [Text Block] Reinsurance Reinsurance [Text Block] Other Operating Expenses And Other Expenses [Abstract] Schedule of other operating expenses Schedule of Other Operating Cost and Expense, by Component [Table Text Block] Schedule of other expenses Schedule of Other Nonoperating Income (Expense) [Table Text Block] RSUs Restricted Stock Units (RSUs) [Member] Undesignated preferred stock, shares authorized Undesignated stock par value (in dollars per share) Common shares reserved for future issuance Common Stock, Capital Shares Reserved for Future Issuance Restricted stock unit dividend equivalents Restricted Stock Unit Dividend Equivalents Represents amount of dividend equivalent of RSU's. Dividends payable Dividends Payable Goodwill and Intangible Assets Disclosure [Abstract] Goodwill and Intangible Assets Goodwill and Intangible Assets Disclosure [Text Block] Equity Awards Shareholders' Equity and Share-based Payments [Text Block] SEC Schedule, 12-17, Insurance Companies, Reinsurance [Table] SEC Schedule, 12-17, Insurance Companies, Reinsurance [Table] SEC Schedule, 12-17, Insurance Companies, Reinsurance [Line Items] SEC Schedule, 12-17, Insurance Companies, Reinsurance [Line Items] Direct Written Premiums Ceded to Other Companies Written Premiums Assumed from Other Companies Written Premiums Percentage of Amount Assumed to Net SEC Schedule, 12-17, Insurance Companies, Reinsurance, Premium, Percentage Assumed to Net Other Operating Expenses and Other Expenses Other Operating Expenses And Other Expenses [Text Block] Represents entire disclosure of Other operating expenses and other expenses. Schedule of deferred policy acquisition costs Deferred Policy Acquisition Costs [Table Text Block] Risk-free interest rate Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Risk Free Interest Rate Dividend yield Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Expected Dividend Rate Expected share price volatility Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Expected Volatility Rate Expected life (in years) Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Expected Term Net reserve for losses and loss adjustment expenses Liability for Unpaid Claims and Claims Adjustment Expense, Net Reserve for losses and loss adjustment expenses gross of reinsurance recoverables on unpaid losses and loss adjustment expenses at end of period Incurred Losses and Loss Adj Expenses IBNR Liability for Unpaid Claims and Claims Adjustment Expense, Incurred but Not Reported (IBNR) Claims, Amount Cumulative Number of Reported Claims Short-duration Insurance Contract, Cumulative Number of Reported Claims Segment Information Segment Reporting Disclosure [Text Block] Schedule of weighted-average tax rate as well as a reconciliation to total tax expense Schedule of Effective Income Tax Rate Reconciliation [Table Text Block] Schedule of deferred tax asset at the current prevailing corporate income tax rate Schedule of Deferred Tax Assets and Liabilities [Table Text Block] Schedule Of Acquired Intangible Assets [Table] Schedule Of Acquired Intangible Assets [Table] Represents the tabular information related to intangible assets acquired in the acquisition. Indefinite-lived Intangible Assets [Axis] Indefinite-lived Intangible Assets [Axis] Indefinite-lived Intangible Assets, Major Class Name [Domain] Indefinite-lived Intangible Assets, Major Class Name [Domain] Trademarks Trademarks [Member] Insurance licenses and authorities Licensing Agreements [Member] Finite-Lived Intangible Assets by Major Class [Axis] Finite-Lived Intangible Assets by Major Class [Axis] Finite-Lived Intangible Assets, Major Class Name [Domain] Finite-Lived Intangible Assets, Major Class Name [Domain] Broker relationships Broker Relationships [Member] Represents information related to broker relationships. Acquired Intangible Assets [Line Items] Acquired Intangible Assets [Line Items] Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table. Identifiable intangibles not subject to amortization Indefinite-lived Intangible Assets (Excluding Goodwill) Identifiable intangible assets subject to amortization Finite-Lived Intangible Assets, Net [Abstract] Gross Carrying Amount Finite-Lived Intangible Assets, Gross Accumulated Amortization Finite-Lived Intangible Assets, Accumulated Amortization Total intangible assets, gross Intangible Assets, Gross (Excluding Goodwill) Weighted-Average Life (in years) Finite-Lived Intangible Asset, Useful Life Statutory Matters [Abstract] Statutory Matters Minimum statutory solvency margin Statutory Accounting Practices, Statutory Capital and Surplus Required Actual statutory capital and surplus Statutory Accounting Practices, Statutory Capital and Surplus, Balance Statutory net income Statutory Accounting Practices, Statutory Net Income Amount Minimum liquidity ratio Minimum Liquidity Ratio Represents minimum liquidity ratio required to be maintained. Debt Disclosure [Abstract] Line of Credit Facility [Table] Line of Credit Facility [Table] Debt Instrument [Axis] Debt Instrument [Axis] Debt Instrument, Name [Domain] Debt Instrument, Name [Domain] 2013 Facility 2013 Facility [Member] Represents letter of credit facility 102.5 million. 2017 Facility 2017 Facility [Member] 2017 Facility James River Group Senior Debt James River Group Senior Debt [Member] James River Group Senior Debt [Member] Variable Rate [Axis] Variable Rate [Axis] Variable Rate [Domain] Variable Rate [Domain] LIBOR London Interbank Offered Rate (LIBOR) [Member] Long-term Debt, Type [Axis] Long-term Debt, Type [Axis] Long-term Debt, Type [Domain] Long-term Debt, Type [Domain] Secured Secured Debt [Member] Unsecured Unsecured Debt [Member] Lender Name [Axis] Lender Name [Axis] Line of Credit Facility, Lender [Domain] Line of Credit Facility, Lender [Domain] JRG Re Jrg Re [Member] Represents information about JRG Re. Line of Credit Facility [Line Items] Line of Credit Facility [Line Items] Current total capacity Line of Credit Facility, Current Borrowing Capacity Maximum borrowing capacity Line of Credit Facility, Maximum Borrowing Capacity Letters of credit outstanding Letters of Credit Outstanding, Amount Margin above LIBOR, percentage rate Long-term Debt, Percentage Bearing Variable Interest, Percentage Rate Amount outstanding on line of credit Long-term Line of Credit Commitment to lend Commitment To Lend Represents amount commitment to lend. Principal amount of Senior Debt Debt Instrument, Face Amount 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] Deferred policy acquisition costs Deferred Policy Acquisition Cost Represents costs related to successful acquisition of insurance that are deferred. Amortization of policy acquisition costs Amortization Of Policy Acquisition Costs Represents amortization of policy acquisition costs. Net realized investment losses (gains) Marketable Securities, Realized Gain (Loss) Impairment of intangible assets Impairment of Intangible Assets (Excluding Goodwill) Income from equity method investments Trading securities purchases, sales, and maturities, net Increase (Decrease) in Debt Securities, Trading, and Equity Securities, FV-NI Deferred U.S. federal income tax (benefit) expense Provision for depreciation and amortization Depreciation, Depletion and Amortization Share based compensation expense Share-based Compensation Excess tax benefits from equity incentive plan transactions Excess Tax Benefit from Share-based Compensation, Operating Activities Change in operating assets and liabilities: Increase (Decrease) in Operating Capital [Abstract] Reserve for losses and loss adjustment expenses Increase (Decrease) in Liability for Claims and Claims Adjustment Expense Reserve Unearned premiums Increase (Decrease) in Unearned Premiums Premiums receivable and agents’ balances Increase (Decrease) in Premiums Receivable Reinsurance balances Increase (Decrease) in Reinsurance Recoverable Payable to insurance companies Increase (Decrease) in Reinsurance Payables Other Increase (Decrease) in Other Operating Assets and Liabilities, Net 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] Securities available-for-sale: Debt Securities, Available-for-sale [Abstract] Purchases – fixed maturity securities Payments to Acquire Debt Securities, Available-for-sale Sales – fixed maturity securities Proceeds from Sale of Debt Securities, Available-for-sale Maturities and calls – fixed maturity securities Proceeds from Maturities, Prepayments and Calls of Debt Securities, Available-for-sale Purchases – equity securities Payments to Acquire Trading Securities Held-for-investment Sales – equity securities Proceeds from Sale of Debt and Equity Securities, FV-NI, Held-for-investment Bank loan participations: Bank Loan Participations [Abstract] Purchases Payment To Acquire Bank Loan Participations Represents payment to acquire Bank loan participations. Sales Proceeds From Bank Loan Participations Represents cash inflow from sales of bank loan participations. Maturities Proceeds From Maturities From Bank Loan Participations Represents cash inflow from maturities of bank loan participations. Other invested assets: Other Investments [Abstract] Purchases Payments to Acquire Other Investments Return of capital Proceeds From Other Invested Asset Return Of Capital Represents cash inflow from other invested asset return of capital. Maturities and repayments Proceeds From Maturities And Repayments Of Other Invested Assets Represents proceeds from maturities and repayments of other invested assets. Securities receivable or payable, net Payments for (Proceeds from) Investments Short-term investments, net Payments for (Proceeds from) Short-term Investments Other Payments for (Proceeds from) Other Investing Activities 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] Senior debt issuances Proceeds from Issuance of Senior Long-term Debt Senior debt repayments Repayments of Senior Debt Dividends paid Payments of Dividends Issuances of common shares under equity incentive plans Proceeds from Issuance of Shares under Incentive and Share-based Compensation Plans, Including Stock Options Common share repurchases Payments for Repurchase of Common Stock Other financing activities Proceeds from (Payments for) Other Financing Activities Net cash used in financing activities Net Cash Provided by (Used in) Financing Activities Change in cash and cash equivalents Cash and Cash Equivalents, Period Increase (Decrease) Cash and cash equivalents at beginning of year Cash and cash equivalents at end of year Supplemental information Supplemental Cash Flow Information [Abstract] Income taxes paid (refunded), net Income Taxes Paid, Net Interest paid Interest Paid, Excluding Capitalized Interest, Operating Activities Outstanding losses and loss adjustment expenses assumed from involuntary workers compensation pools Outstanding Losses And Loss Adjustment Expenses Assumed From Involuntary Workers Compensation Pools This element represents amount of outstanding losses and loss adjustment expenses assumed from involuntary workers compensation pools. Claims outstanding Ceded Credit Risk [Table] Ceded Credit Risk [Table] Ceded Credit Risk, Reinsurer [Axis] Ceded Credit Risk, Reinsurer [Axis] Ceded Credit Risk, Reinsurer [Domain] Ceded Credit Risk, Reinsurer [Domain] Largest reinsurer one Credit Risk Reinsurer One [Member] Represents information about credit risk reinsurer one. Largest reinsurer two Credit Risk Reinsurer Two [Member] Represents information about Credit Risk Reinsurer two. Largest reinsurer three Credit Risk Reinsurer Three [Member] Represents information about Credit Risk Reinsurer three. Ceded Credit Risk [Line Items] Ceded Credit Risk [Line Items] Percentage of reinsurance recoverables on unpaid losses for 3 largest reinsurers Reinsurance Recoverables On Unpaid Losses Percentage Of Total Balance Represents reinsurance recoverables on unpaid losses percentage of total balance. Prepaid reinsurance premiums ceded Percentage of prepaid reinsurance premiums ceded for 3 largest reinsurers Prepaid Reinsurance Premiums Ceded Percentage Of Total Balance Represents prepaid reinsurance premiums ceded as percentage of total balance. Employee severance Severance Costs Income on leased building the Company is deemed to own for accounting purposes (see Note 21) Operating Lease, Lease Income Legal and professional services related to secondary share offerings Legal, Tax, And Other Professional Services Expense Represents the amount related to legal, tax, and other professional services. Other Other Expense, Miscellaneous Other Expense, Miscellaneous Impairment of intangible asset Impairment of Intangible Assets, Indefinite-lived (Excluding Goodwill) Total Basis of Presentation and Principles of Consolidation Basis of Accounting, Policy [Policy Text Block] Estimates and Assumptions Use of Estimates, Policy [Policy Text Block] Fixed Maturity and Equity Securities Marketable Securities, Policy [Policy Text Block] Bank Loan Participations Held-for-Investment and Allowance for Credit Losses Finance, Loan and Lease Receivables, Held-for-investment, Policy [Policy Text Block] Other Invested Assets Other Invested Assets [Policy Text Block] Represents disclosure of accounting policy for other invested assets composition and accounting. Short-Term Investments Investment, Policy [Policy Text Block] Cash Equivalents Cash and Cash Equivalents, Policy [Policy Text Block] Direct Written Premiums Revenue Recognition, Premiums Earned, Policy [Policy Text Block] Assumed Reinsurance Premiums Assumed Reinsurance Premiums [Policy Text Block] Represents disclosure of accounting policy for assumed Reinsurance Premiums. Premiums Receivable and Agents' Balances, Net Premiums Receivable, Basis of Accounting, Policy [Policy Text Block] Deferred Policy Acquisition Costs Deferred Policy Acquisition Costs, Policy [Policy Text Block] Reinsurance and Adjustable Features of Insurance and Reinsurance Contracts Reinsurance Accounting Policy [Policy Text Block] Other Income Other Income [Policy Text Block] Represents disclosure of accounting policy for other income composition and revenue recognition policy. Income Taxes Income Tax, Policy [Policy Text Block] Goodwill Goodwill and Intangible Assets, Goodwill, Policy [Policy Text Block] Intangible Assets, Net Goodwill and Intangible Assets, Policy [Policy Text Block] Impairment of Long-Lived Assets Impairment or Disposal of Long-Lived Assets, Policy [Policy Text Block] Property and Equipment, Net Property, Plant and Equipment, Policy [Policy Text Block] Reserve for Losses and Loss Adjustment Expenses Liability Reserve Estimate, Policy [Policy Text Block] Share Based Compensation Share-based Compensation, Option and Incentive Plans Policy [Policy Text Block] Financing Obligations Asset Retirement Obligation [Policy Text Block] Variable Interest Entities Consolidation, Variable Interest Entity, Policy [Policy Text Block] Earnings Per Share Earnings Per Share, Policy [Policy Text Block] Adopted and Prospective Accounting Standards New Accounting Pronouncements, Policy [Policy Text Block] Deferred tax assets: Deferred Tax Assets, Net [Abstract] Accrued compensation expenses Deferred Tax Assets, Tax Deferred Expense, Compensation and Benefits, Employee Compensation Reserve for losses and loss adjustment expenses Deferred Tax Assets, Tax Deferred Expense, Reserves and Accruals, Loss Reserves Unearned premiums Deferred Tax Assets, Tax Deferred Expense, Reserves and Accruals, Unearned Premiums Reserve Share based compensation Deferred Tax Assets, Tax Deferred Expense, Compensation and Benefits, Share-based Compensation Cost Allowance for doubtful accounts Deferred Tax Assets, Tax Deferred Expense, Reserves and Accruals, Allowance for Doubtful Accounts Deferred policy acquisition costs Deferred Tax Assets Deferred Policy Acquisition Costs Represents amount before allocation of valuation allowances of deferred tax asset attributable to deductible temporary differences from the Deferred policy acquisition costs. Property and equipment Deferred Tax Assets, Property, Plant and Equipment Invested asset impairments Deferred Tax Assets, Tax Deferred Expense, Reserves and Accruals, Impairment Losses Other Deferred Tax Assets, Other Total deferred tax assets Deferred Tax Assets, Gross Deferred tax liabilities: Components of Deferred Tax Liabilities [Abstract] Intangible assets Deferred Tax Liabilities, Intangible Assets Net unrealized gains Deferred Tax Liabilities, Other Comprehensive Income Deferred policy acquisition costs Deferred Tax Liabilities, Deferred Expense, Deferred Policy Acquisition Cost Equity method investments Deferred Tax Liabilities, Investment in Noncontrolled Affiliates Other Deferred Tax Liabilities, Other Total deferred tax liabilities Deferred Tax Liabilities, Gross Net deferred tax assets Deferred Tax Assets, Net Net deferred tax assets (liabilities) Deferred Tax Liabilities, Net Intangible Assets [Roll Forward] Finite-lived Intangible Assets [Roll Forward] Net Carrying Value Amortization Impairment Losses Net Carrying Value Statutory capital and surplus Minimum required statutory capital and surplus Employee Benefits and Share-based Compensation, Noncash [Abstract] Employee Benefits Compensation and Employee Benefit Plans [Text Block] Subordinated Borrowings [Abstract] Schedule of Junior Subordinated Debt Schedule of Subordinated Borrowing [Table Text Block] Income Tax Examination [Table] Income Tax Examination [Table] Geographical [Axis] Geographical [Axis] Geographical [Domain] Geographical [Domain] Bermuda Income Tax Examination [Line Items] Income Tax Examination [Line Items] Percentage of dividend withholding tax Percentage Of Dividend Withholding Tax Represents percentage of dividend withholding tax. Dividend distributions to intermediate holding company Dividend Distributions To Intermediate Holding Company Represents dividend distributions to intermediate holding company. Deferred tax asset for additional discount Tax Cuts And Jobs Act Of 2017, Incomplete Accounting, Change In Tax Rate, Deferred Tax Asset, Provisional Income Tax Expense Tax Cuts And Jobs Act Of 2017, Incomplete Accounting, Change In Tax Rate, Deferred Tax Asset, Provisional Income Tax Expense Deferred tax liability Tax Cuts and Jobs Act of 2017, Change in Tax Rate, Deferred Tax Liability, Income Tax Benefit Tax Cuts and Jobs Act of 2017, Change in Tax Rate, Deferred Tax Liability, Income Tax Benefit Transition provision expense Tax Cuts and Jobs Act of 2017, Change in Tax Rate, Income Tax Expense (Benefit) Tax Cuts and Jobs Act of 2017, Change in Tax Rate, Income Tax Expense (Benefit) Remittance of dividend withholding tax Dividend Withholding Tax Remittance Represents dividend withholding tax remittance. Federal statutory tax rates Effective Income Tax Rate Reconciliation, at Federal Statutory Income Tax Rate, Percent U.S. income before Federal income taxes Income (Loss) from Continuing Operations before Income Taxes, Domestic Percentage of excise tax on reinsurance premiums paid Excise Tax On Reinsurance Premiums Paid Represents excise tax on reinsurance premiums paid. Payment of federal excise taxes Payment Of Federal Excise Taxes Represents payment of federal excise taxes on intercompany reinsurance transactions. Excise taxes paid Excise Taxes Paid Represents excise taxes paid on written premiums assumed from third-party insurers with respect to risks located in the U.S. Schedule of future minimum payments under non-cancelable operating leases Schedule of Future Minimum Rental Payments for Operating Leases [Table Text Block] Net realized investment (losses) gains Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI for Sale of Securities, before Tax Bank loan participations realized investment gains (losses) Related Party Transactions [Abstract] Schedule of Related Party Transactions, by Related Party [Table] Schedule of Related Party Transactions, by Related Party [Table] Subsequent Event Type [Axis] Subsequent Event Type [Axis] Subsequent Event Type [Domain] Subsequent Event Type [Domain] Subsequent event Subsequent Event [Member] Adjustments for New Accounting Pronouncements [Axis] Adjustments for New Accounting Pronouncements [Axis] Type of Adoption [Domain] Type of Adoption [Domain] ASU 2016-02 Accounting Standards Update 2016-02 [Member] Related Party [Axis] Related Party [Axis] Related Party [Domain] Related Party [Domain] Non-Executive Chairman Non-Executive Chairman [Member] Non-Executive Chairman [Member] Independent Directors Director [Member] Agreement [Axis] Agreement [Axis] Information of agreement. Agreement [Domain] Agreement [Domain] Information of agreement. Consulting Agreement Consulting Agreement [Member] Information of consulting agreement. Related Party Transaction [Line Items] Related Party Transaction [Line Items] Lease term (in years) Lessee, Operating Lease, Term of Contract Increase in fixed annual rent Increase In Fixed Annual Rent Represents percentage increase in fixed annual rent. Assets Liabilities Cumulative effect of adoption of ASU Cumulative Effect of New Accounting Principle in Period of Adoption Total fees paid for the use of plane Related Party Transaction, Amounts of Transaction Investment and other business consulting services fees Professional Fees Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Table] Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Table] Available-for-sale fixed maturity and equity securities Debt and Equity Securities [Member] Debt and Equity Securities [Member] Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items] Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items] Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward] Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward] Beginning balance Transfers out of Level 3 Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Transfers out of Level 3 Transfers in to Level 3 Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Transfers Into Level 3 Purchases Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Purchases Sales Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Sales Maturities and calls Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Settlements Amortization of discount Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Period Increase (Decrease) Total gains or losses (realized/unrealized) - Included in earnings Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Gain (Loss) Included in Earnings Total gains or losses (realized/unrealized) - Included in other comprehensive income Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Gain (Loss) Included in Other Comprehensive Income (Loss) Ending balance SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Table] SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Table] Debt Security Category [Axis] Debt Security Category [Axis] Other than Temporary Impairment, Credit Losses Recognized in Earnings, Categories of Investments [Domain] Other than Temporary Impairment, Credit Losses Recognized in Earnings, Categories of Investments [Domain] Available-for-sale Securities Available-for-sale Securities [Member] Bank loan participations, held-for-investment, net of allowance Short-term investments Short-term Investments [Member] Other invested assets Other Security Investments [Member] SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items] SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items] Cost or Amortized Cost SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties, Cost Fair Value SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties, Fair Value Amount at which shown on Balance Sheet SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties, Amount Quarterly Financial Data [Abstract] Unaudited Selected Quarterly Financial Data Quarterly Financial Information [Text Block] Date Of Declaration [Axis] Date Of Declaration [Axis] Represents information about date of declaration. Date Of Declaration [Domain] Date Of Declaration [Domain] Represents information about date of declaration. November 1, 2017 Date Of Declaration November 1, 2017 [Member] Date Of Declaration November 1, 2017 [Member] November 1, 2017 Date Of Declaration November 1, 2017 One [Member] Date Of Declaration November 1, 2017 One [Member] November 1, 2016 Date Of Declaration November 1, 2016 [Member] Represents date of dividend declaration. November 1, 2016 Date Of Declaration November 1, 2016 One [Member] Represents date of dividend declaration. Dividend declared per share (in dollars per share) Total Amount Dividends, Common Stock, Cash Dividend Restrictions Dividend Payment Restrictions [Text Block] Investments Investment [Text Block] Contingent Liabilities [Table] Contingent Liabilities [Table] Discloses information about contingent liabilities. JRG Reinsurance Company, Ltd. Captive insurance company affiliate of the insured group Affiliated Entity [Member] Credit Facility [Axis] Credit Facility [Axis] Credit Facility [Domain] Credit Facility [Domain] Letter of credit 100 million Letter Of Credit 100 Million [Member] Represents letter of credit facility of 100.0 million. 2013 Facility Policy management software Computer Software, Intangible Asset [Member] Contingent Liabilities [Line Items] Contingent Liabilities [Line Items] Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table. Rental expense Operating Leases, Rent Expense Future minimum lease payments for building constructed Future Minimum Lease Payments For Building Constructed Represents future minimum lease payments for building constructed. Total payments under lease Operating Leases, Future Minimum Payments Due Letter of credit facilities Number of Letter of Credit Facilities Number of Letter of Credit Facilities Lease payment per year Operating Leases, Rent Expense, Minimum Rentals Letters of credit facility, amount Letter Of Credit Facility Amount Represents amount of letter of credit facility. Amount of letters of credit issued Assets deposited for securing letters of credit Assets Deposited For Securing Letters Of Credit Represents amount of assets deposited for securing letters of credit. Total amount deposited in trust accounts Assets Held-in-trust Cash equivalent collateral held in the collateral trust arrangement Assets Held-in-trust, Current Maximum matching employer contribution Defined Contribution Plan, Employer Matching Contribution, Percent of Match Expense associated with Savings Plans Defined Contribution Plan, Cost Nonrecurring basis Fair Value, Measurements, Nonrecurring [Member] Bank loan participations held-for-investment Amortized Cost Debt Securities, Available-for-sale, Amortized Cost, Fiscal Year Maturity [Abstract] One year or less Debt Securities, Available-for-sale, Maturity, Allocated and Single Maturity Date, within One Year, Amortized Cost After one year through five years Debt Securities, Available-for-sale, Maturity, Allocated and Single Maturity Date, after One Through Five Years, Amortized Cost After five years through ten years Debt Securities, Available-for-sale, Maturity, Allocated and Single Maturity Date, after Five Through Ten Years, Amortized Cost After ten years Debt Securities, Available-for-sale, Allocated and Single Maturity Date, Maturity, after 10 Years, Amortized Cost Residential mortgage-backed Residential Mortgage Backed Amortized Cost Represents Amortized Cost of Residential mortgage-backed securities. Commercial mortgage and asset-backed Commercial Mortgage And Asset Backed Amortized Cost Represents amortized cost of commercial mortgage and asset-backed. Redeemable preferred stock Redeemable Preferred Stock Amortized Cost Represents amortized cost of redeemable preferred stock. Fair Value Debt Securities, Available-for-sale, Fair Value, Fiscal Year Maturity [Abstract] One year or less Debt Securities, Available-for-sale, Maturity, Allocated and Single Maturity Date, within One Year, Fair Value After one year through five years Debt Securities, Available-for-sale, Maturity, Allocated and Single Maturity Date, after One Through Five Years, Fair Value After five years through ten years Debt Securities, Available-for-sale, Maturity, Allocated and Single Maturity Date, after Five Through Ten Years, Fair Value After ten years Debt Securities, Available-for-sale, Maturity, Allocated and Single Maturity Date, after 10 Years, Fair Value Residential mortgage-backed Residential Mortgage Backed Fair Value Represents fair value of residential mortgage backed. Commercial mortgage and asset-backed Commercial Mortgage And Asset Backed Fair Value Represents fair value of commercial mortgage and asset backed. Redeemable preferred stock Redeemable Preferred Stock Fair Value Represents fair value of Redeemable preferred stock. Total, Fair Value Product and Service [Axis] Product and Service [Axis] Product and Service [Domain] Product and Service [Domain] Manufacturers and Contractors Manufacturers And Contractors [Member] Name of underwriting division. Excess Casualty Excess Casualty [Member] Name of underwriting division. General Casualty General Casualty [Member] Name of underwriting division. Energy Energy [Member] Name of underwriting division. Allied Health Allied Health [Member] Name of underwriting division. Excess Property Excess Property [Member] Name of underwriting division. Life Sciences Life Sciences [Member] Name of underwriting division. Small Business Small Business [Member] Name of underwriting division. Professional Liability Professional Liability [Member] Name of underwriting division. Environmental Environmental [Member] Name of underwriting division. Medical Professionals Medical Professionals [Member] Name of underwriting division. Sports and Entertainment Sports And Entertainment [Member] Name of underwriting division. Total gross written premiums Senior Debt Debt Disclosure [Text Block] Statements of financial information of parent company only (Parent Company) Condensed Financial Information of Parent Company Only Disclosure [Text Block] Income Statement Location [Axis] Income Statement Location [Axis] Income Statement Location [Domain] Income Statement Location [Domain] Commission expense Selling and Marketing Expense [Member] Total revenues Comprehensive (loss) income Earnings per share: SEC Schedule, 12-18, Supplemental Information, Property-Casualty Insurance Underwriters [Abstract] Supplementary Information Concerning Property Casualty Insurance Operations SEC Schedule, 12-18, Supplemental Information, Property-Casualty Insurance Underwriters [Text Block] Schedule of Business Acquisitions, by Acquisition [Table] Schedule of Business Acquisitions, by Acquisition [Table] State Licenses License [Member] Business Acquisition [Axis] Business Acquisition [Axis] Business Acquisition, Acquiree [Domain] Business Acquisition, Acquiree [Domain] James River Group, Inc. James River Group Inc [Member] Represents information regarding James River Group, Inc. Business Acquisition [Line Items] Business Acquisition [Line Items] Percentage of outstanding shares acquired Business Acquisition, Percentage of Voting Interests Acquired Goodwill impairment Goodwill, Impairment Loss Accumulated goodwill impairment losses Goodwill, Impaired, Accumulated Impairment Loss Schedule of summary of company's segment results Schedule of Segment Reporting Information, by Segment [Table Text Block] Schedule of underwriting profit (loss) of operating segments by individual segment and reconciliation to consolidated income before taxes Reconciliation of Operating Profit (Loss) from Segments to Consolidated [Table Text Block] Schedule of gross written premiums by segment and underwriting division Reconciliation of Revenue from Segments to Consolidated [Table Text Block] Amortization of policy acquisition costs Other underwriting expenses of the insurance segments Other Underwriting Expense Other operating expenses of the Corporate and Other segment Total Schedule of components of comprehensive income Comprehensive Income (Loss) [Table Text Block] Schedule of summary of option activity Share-based Compensation, Stock Options, Activity [Table Text Block] Schedule of value of the options granted was estimated at the date of grant using the Black-Scholes-Merton Schedule of Share-based Payment Award, Stock Options, Valuation Assumptions [Table Text Block] Schedule of summary of RSU activity Schedule of Nonvested Restricted Stock Units Activity [Table Text Block] Schedule of summary of amount of expense and related tax benefit Schedule of Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Table Text Block] Subsequent Event [Table] Subsequent Event [Table] Line of Credit Line of Credit [Member] Plan Name [Axis] Plan Name [Axis] Plan Name [Domain] Plan Name [Domain] 2014 Long Term Incentive Plan Long Term Incentive Plan 2014 [Member] Represents information regarding Long Term Incentive Plan 2014. Subsequent Event [Line Items] Subsequent Event [Line Items] Dividends payable, per common share Dividends Payable, Amount Per Share Vesting period (in years) Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Period Number of awards granted Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period Fair value on grant date Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period, Weighted Average Grant Date Fair Value Repayments of unsecured borrowings Repayments of Unsecured Debt Unsecured loans outstanding Unsecured Debt Less Than 12 Months, Fair Value Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months Less Than 12 Months, Unrealized Losses Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss 12 Months or More, Fair Value Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer 12 Months or More, Gross Unrealized Losses Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss Total, Fair Value Debt Securities, Available-for-sale, Unrealized Loss Position Total, Gross Unrealized Losses Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss 2019 Finite-Lived Intangible Assets, Amortization Expense, Next Twelve Months 2020 Finite-Lived Intangible Assets, Amortization Expense, Year Two 2021 Finite-Lived Intangible Assets, Amortization Expense, Year Three 2022 Finite-Lived Intangible Assets, Amortization Expense, Year Four 2023 Finite-Lived Intangible Assets, Amortization Expense, Year Five Thereafter Finite-Lived Intangible Assets, Amortization Expense, after Year Five Total Finite-Lived Intangible Assets, Net Schedule of statutory accounting Statutory Accounting Practices Disclosure [Table Text Block] Accident years 2014 through 2016 Accident Years 2016, 2015, and 2014 [Member] Accident Years 2016, 2015, and 2014 [Member] Accident years at least four years old Short-duration Insurance Contracts, Accident Years At Least Four Years Old [Member] Short-duration Insurance Contracts, Accident Years At Least Four Years Old [Member] Accident years 2010 through 2014 Accident Years 2010 Through 2014 [Member] Information about favorable reserve development in 2010 through 2014 accident year. Accident years 2010 through 2015 Short-duration Insurance Contracts, Accident Years 2010 Through 2015 [Member] Short-duration Insurance Contracts, Accident Years 2010 Through 2015 [Member] Accident years 2010 through 2013 Short-duration Insurance Contracts, Accident Years 2010 Through 2013 [Member] Short-duration Insurance Contracts, Accident Years 2010 Through 2013 [Member] Accident years 2012 and 2013 Short-duration Insurance Contracts, Accident Years 2012 and 2013 [Member] Short-duration Insurance Contracts, Accident Years 2012 and 2013 [Member] Favorable development on prior year loss reserves Development On Prior Year Loss Reserves [Abstract] Reserves for losses and loss adjustment expenses Prior Year Claims and Claims Adjustment Expense SEC Schedule, 12-09, Valuation and Qualifying Accounts Disclosure [Table] SEC Schedule, 12-09, Valuation and Qualifying Accounts Disclosure [Table] SEC Schedule, 12-09, Valuation Allowances and Reserves Type [Axis] SEC Schedule, 12-09, Valuation Allowances and Reserves Type [Axis] SEC Schedule, 12-09, Valuation Allowances and Reserves [Domain] SEC Schedule, 12-09, Valuation Allowances and Reserves [Domain] Allowance for Doubtful Accounts SEC Schedule, 12-09, Allowance, Credit Loss [Member] Allowance for Credit Losses on Bank Loans SEC Schedule, 12-09, Allowance, Loss on Finance Receivable [Member] SEC Schedule, 12-09, Valuation and Qualifying Accounts Disclosure [Line Items] SEC Schedule, 12-09, Valuation and Qualifying Accounts Disclosure [Line Items] SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward] SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward] Balance at Beginning of Period SEC Schedule, 12-09, Valuation Allowances and Reserves, Amount Additions Amounts Charged to Expense SEC Schedule, 12-09, Valuation Allowances and Reserves, Additions, Charge to Cost and Expense Deductions Amounts Written Off or Disposals SEC Schedule, 12-09, Valuation Allowances and Reserves, Deduction Balance at End of Period Schedule of reconciliation of numerator and denominator of basic and diluted earnings per share Schedule of Earnings Per Share, Basic and Diluted [Table Text Block] 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 Thereafter Operating Leases, Future Minimum Payments, Due Thereafter Total Renewable Energy Bridge Financing Notes Credit Rating, Standard & Poor's [Axis] Credit Rating, Standard & Poor's [Axis] External Credit Rating, Standard & Poor's [Domain] External Credit Rating, Standard & Poor's [Domain] Standard & Poor's, BBB- Rating Standard & Poor's, BBB- Rating [Member] Puerto Rico loan Puerto Rico Loan [Member] Represents information about Puerto Rico Loan. Impaired bank loans Impaired Bank Loans [Member] Impaired Bank Loans [Member] Number of available-for-sale securities held in an unrealized loss position Debt Securities, Available-for-sale, Unrealized Loss Position, Number of Positions Total fair value of unrealized loss position securities Gross unrealized losses Percentage of available for sale securities Percentage Of Available For Sale Securities Represents percentage of available for sale securities. Impairment loss Other than Temporary Impairment Losses, Investments, Available-for-sale Securities Allowance for credit losses Impaired Financing Receivable, Related Allowance Carrying value of loan Unpaid principal on impaired loans Impaired Financing Receivable, Unpaid Principal Balance Carrying value of impaired loans Loan And Advances Carrying Value Represents the carrying value of impaired loans. Number of impaired loans Number Of Impaired Loans Represents the number of impaired loans. Trading securities, realized gain (loss) Trading Securities, Realized Gain (Loss) Average recorded investment in impaired bank loans Impaired Financing Receivable, Average Recorded Investment Net Investment Income Net realized gain (loss) on changes in fair value of impaired bank loans Realized Gain Loss On Changes In Fair Value Of Impaired Bank Loans This item represents the Net realized gain (loss) on changes in fair value of impaired bank loans. Unamortized discount Debt Instrument, Unamortized Discount Unamortized premium Debt Instrument, Unamortized Premium Dividend income Investment Income, Dividend Gross realized gains Available-for-sale Securities, Gross Realized Gains Investment as collateral for outstanding letters of credit Security Owned and Pledged as Collateral, Fair Value Investments on deposit with state insurance departments Cash, Cash Equivalents, and Short-term Investments Deferred Policy Acquisition Costs Deferred Policy Acquisition Costs [Text Block] Other Related Party Transactions Related Party Transactions Disclosure [Text Block] Schedule of unaudited quarterly results of operations Quarterly Financial Information [Table Text Block] Statutory Matters Statutory Matters [Text Block] The entire disclosure represents information regarding insurance statutory matters. Net earned premiums Segment revenues Segment goodwill Segment assets Schedule of Long-term Debt Instruments [Table] Schedule of Long-term Debt Instruments [Table] Junior Subordinated Debt [Member] Junior Subordinated Debt [Member] Debt Instrument, Redemption, Period [Axis] Debt Instrument, Redemption, Period [Axis] Debt Instrument, Redemption, Period [Domain] Debt Instrument, Redemption, Period [Domain] Debt Instrument [Line Items] Debt Instrument [Line Items] Debt redemption percentage Debt Instrument, Redemption Price, Percentage Deferred interest payment period (in years) Debt Instrument, Deferred Interest Option, Maximum Term Debt Instrument, Deferred Interest Option, Maximum Term Unrealized (losses) gains arising during the period, before U.S. income taxes Other Comprehensive Income (Loss), Securities, Available-for-Sale, Unrealized Holding Gain (Loss) Arising During Period, before Tax U.S. income taxes Other Comprehensive Income (Loss), Securities, Available-for-Sale, Unrealized Holding Gain (Loss) Arising During Period, Tax Unrealized (losses) gains arising during the period, net of U.S. income taxes Other Comprehensive Income (Loss), Securities, Available-for-Sale, Unrealized Holding Gain (Loss) Arising During Period, after Tax Less reclassification adjustment: Other Comprehensive Income (Loss), Securities, Available-for-sale, Adjustment, before Reclassification Adjustments, after Tax [Abstract] U.S. income taxes Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI for Sale of Securities, Tax Reclassification adjustment for investment (losses) gains realized in net income Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI for Sale of Securities, Net of Tax Other comprehensive (loss) income Condensed Balance Sheet Statement [Table] Condensed Balance Sheet Statement [Table] Condensed Balance Sheet Statements, Captions [Line Items] Condensed Balance Sheet Statements, Captions [Line Items] Assets [Abstract] Investment in subsidiaries Due from subsidiaries Due from Related Parties Notes payable to subsidiary Notes Payable, Related Parties, Noncurrent Due to subsidiaries Due to Related Parties, Noncurrent Class A common shares Condensed Financial Statements [Table] Condensed Financial Statements [Table] Equity Components [Axis] Equity Components [Axis] Equity Component [Domain] Equity Component [Domain] Retained Earnings Retained Earnings [Member] ASU 2016-01 Accounting Standards Update 2016-01 [Member] ASU 2018-02 Accounting Standards Update 2018-02 [Member] Accounting Standards Update 2018-02 [Member] Condensed Financial Statements, Captions [Line Items] Condensed Financial Statements, Captions [Line Items] Accounting Policies [Table] Accounting Policies [Table] Schedule detailing information related to accounting policies. AOCI AOCI Including Portion Attributable to Noncontrolling Interest [Member] United States Financing Receivables, Period Past Due [Axis] Financing Receivables, Period Past Due [Axis] Financing Receivables, Period Past Due [Domain] Financing Receivables, Period Past Due [Domain] Receivables greater than 90 days past due Financing Receivables, Equal to Greater than 90 Days Past Due [Member] Accounting Policies [Line Items] Accounting Policies [Line Items] Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table. Number of insurance companies Number Of Insurance Companies This element represents number of insurance companies owned by the entity. Number of bank loans on nonaccrual status Number Of Participation Bank Loans On Nonaccrual Status Represents the number of participation bank loans on nonaccrual status. Premiums receivable, past due Financing Receivable, Recorded Investment, Past Due Allowance for doubtful accounts Allowance for Doubtful Accounts Receivable Bad debt expense Provision for Doubtful Accounts Allowance for doubtful accounts receivables written off Allowance for Doubtful Accounts Receivable, Write-offs Intangible assets, useful life (in years) Property and equipment, estimated useful lives (in years) Property, Plant and Equipment, Useful Life Right-of-use assets Operating Lease, Right-of-Use Asset Lease liabilities Operating Lease, Liability Investment in variable interest entities Variable Interest Entity, Reporting Entity Involvement, Maximum Loss Exposure, Amount Common share equivalents excluded from calculations of diluted earnings per share Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount Reduction in basic and diluted earnings per share (in dollars per share) Earnings Per Share, Basic and Diluted Schedule of premiums written, premiums earned, and losses and loss adjustment expenses Effects of Reinsurance [Table Text Block] Title of Individual [Axis] Title of Individual [Axis] Relationship to Entity [Domain] Relationship to Entity [Domain] Non-employee directors Non-employee Directors [Member] Non-employee Directors [Member] 2014 Non-Employee Director Incentive Plan Non Employee Director Incentive Plan 2014 [Member] Represents information regarding 2014 Non Employee Director Incentive Plan. Maximum number of shares available for issuance Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Authorized Number of shares available for grant Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Available for Grant Contractual life of option (in years) Share Based Arrangement By Share Based Award Option Contractual Life Represents Share based arrangement by share based award option Contractual life. Total intrinsic value of options exercised Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercises in Period, Intrinsic Value Aggregate intrinsic value of options outstanding Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Intrinsic Value Aggregate intrinsic value of options exercisable Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercisable, Intrinsic Value Fair value of shares used in calculation of intrinsic values (in dollars per share) Share Price Weighted-average remaining contractual life of options outstanding (in years) Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Remaining Contractual Term Weighted-average remaining contractual life of options exercisable (in years) Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercisable, Weighted Average Remaining Contractual Term Weighted-average fair value of options granted (in dollars per share) Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Weighted Average Grant Date Fair Value 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 Unrecognized share based compensation expense Employee Service Share-based Compensation, Nonvested Awards, Compensation Cost Not yet Recognized Weighted-average period of unrecognized share based compensation expense (in years) Employee Service Share-based Compensation, Nonvested Awards, Compensation Cost Not yet Recognized, Period for Recognition Reserve for Losses and Loss Adjustment Expenses Liability For Claims And Claims Adjustment Expense [Text Block] The entire disclosure for the liability for claims and claims adjustment expense. SEC Schedule, 12-16, Insurance Companies, Supplementary Insurance Information [Table] SEC Schedule, 12-16, Insurance Companies, Supplementary Insurance Information [Table] SEC Schedule, 12-16, Insurance Companies, Supplementary Insurance Information [Line Items] SEC Schedule, 12-16, Insurance Companies, Supplementary Insurance Information [Line Items] Deferred Policy Acquisition Costs SEC Schedule, 12-16, Insurance Companies, Supplementary Insurance Information, Deferred Policy Acquisition Cost Reserve for Losses and Loss Adjustment Expenses SEC Schedule, 12-16, Insurance Companies, Supplementary Insurance Information, Liability for Future Policy Benefit, Loss, Claim and Loss Expense Unearned Premiums SEC Schedule, 12-16, Insurance Companies, Supplementary Insurance Information, Unearned Premium Net Earned Premiums SEC Schedule, 12-16, Insurance Companies, Supplementary Insurance Information, Premium Revenue Net Investment Income SEC Schedule, 12-16, Insurance Companies, Supplementary Insurance Information, Net Investment Income Losses and Loss Adjustment Expenses SEC Schedule, 12-16, Insurance Companies, Supplementary Insurance Information, Benefit, Claim, Loss and Settlement Expenses Amortization of Policy Acquisition Costs SEC Schedule, 12-16, Insurance Companies, Supplementary Insurance Information, Amortization of Deferred Policy Acquisition Cost Other Operating Expenses SEC Schedule, 12-16, Insurance Companies, Supplementary Insurance Information, Other Operating Expense Net Written Premiums SEC Schedule, 12-16, Insurance Companies, Supplementary Insurance Information, Premium Written Available-for-sale securities, change in gross unrealized gains (losses) Other Comprehensive Income (Loss), Securities, Available-for-sale, Adjustment, before Tax Schedule of gross carrying amounts and accumulated amortization Schedule of Intangible Assets and Goodwill [Table Text Block] Schedule of future estimated amortization Schedule of Finite-Lived Intangible Assets, Future Amortization Expense [Table Text Block] Schedule of acquired indefinite-lived intangible assets Schedule of Acquired Indefinite-lived Intangible Assets by Major Class [Table Text Block] Schedule of acquired finite-lived intangible assets Schedule of Acquired Finite-Lived Intangible Assets by Major Class [Table Text Block] Schedule of reconciliation of beginning and ending reserve balances for losses and loss adjustment expenses Schedule of Liability for Unpaid Claims and Claims Adjustment Expense [Table Text Block] Schedule of incurred losses and loss adjustment expenses, net of reinsurance Short-duration Insurance Contracts, Claims Development [Table Text Block] Schedule of reserve for losses and loss adjustment expenses Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Table Text Block] Schedule of average annual percentage payouts of incurred claims by age, net of reinsurance Short-duration Insurance Contracts, Schedule of Historical Claims Duration [Table Text Block] Schedule of incurred but not reported liabilities and claims frequency Schedule Of Incurred But Not Reported Liabilities And Claims Frequency [Table Text Block] Represents information of incurred but not reported Liabilities and claims frequency. Statement of Stockholders' Equity [Abstract] Statement [Table] Statement [Table] Common Shares Additional Paid-in Capital Additional Paid-in Capital [Member] Accumulated Other Comprehensive (Loss) Income AOCI Attributable to Parent [Member] Statement [Line Items] Statement [Line Items] Increase (Decrease) in Stockholders' Equity [Roll Forward] Increase (Decrease) in Stockholders' Equity [Roll Forward] Balances Balances (in shares) Other comprehensive loss Dividends Dividends Exercise of stock options and related excess tax benefits Stock Issued During Period, Value, Stock Options Exercised Exercise of stock options and related excess tax benefits (in shares) Vesting of RSUs and related excess tax benefits Vesting Of Restricted Stock Units And Related Excess Tax Benefits Value Represents the amount related to values of vesting of restricted stock units and related excess tax benefits. Vesting of RSUs and related excess tax benefits (in shares) Vesting Of Restricted Stock Units And Related Excess Tax Benefits Shares Represents the amount related to shares of vesting of restricted stock units and related excess tax benefits. Compensation expense under share incentive plans Adjustments to Additional Paid in Capital, Share-based Compensation, Requisite Service Period Recognition Balances Balances (in shares) Condensed Cash Flow Statement [Table] Condensed Cash Flow Statement [Table] Condensed Cash Flow Statements, Captions [Line Items] Condensed Cash Flow Statements, Captions [Line Items] Adjustments to reconcile net income to net cash (used in) provided by operating activities: Equity in undistributed earnings of subsidiaries Income (Loss) from Equity Method Investments, Net of Dividends or Distributions Changes in operating assets and liabilities: Increase (Decrease) in Operating Capital Dividends from subsidiaries Proceeds from Equity Method Investment, Distribution, Return of Capital Senior debt issuance Subsidiary note repayments Repayments of Related Party Debt Debt issue costs paid Payments of Debt Issuance Costs Issuances of common shares under equity incentive plans Common share repurchases Increase in cash and cash equivalents Interest paid Liability for Unpaid Claims and Claims Adjustment Expense, Period Increase (Decrease) [Abstract] Liability for Unpaid Claims and Claims Adjustment Expense, Period Increase (Decrease) [Abstract] Reserve for losses and loss adjustment expenses net of reinsurance recoverables at beginning of period Add: Incurred losses and loss adjustment expenses net of reinsurance: Liability for Unpaid Claims and Claims Adjustment Expense, Incurred Claims [Abstract] Current year Current Year Claims and Claims Adjustment Expense Prior years Total incurred losses and loss and adjustment expenses Deduct: Loss and loss adjustment expense payments net of reinsurance: Liability for Unpaid Claims and Claims Adjustment Expense, Claims Paid [Abstract] Current year Liability for Unpaid Claims and Claims Adjustment Expense, Claims Paid, Current Year Prior years Liability for Unpaid Claims and Claims Adjustment Expense, Claims Paid, Prior Years Total loss and loss adjustment expense payments Liability for Unpaid Claims and Claims Adjustment Expense, Claims Paid Reserve for losses and loss adjustment expenses net of reinsurance recoverables at end of period Add: Reinsurance recoverables on unpaid losses and loss adjustment expenses at end of period Deferred policy acquisition costs SEC Schedule, 12-18, Supplemental Information, Property-Casualty Insurance Underwriters, Deferred Policy Acquisition Cost Reserve for losses and loss adjustment expenses SEC Schedule, 12-18, Supplemental Information, Property-Casualty Insurance Underwriters, Reserve for Unpaid Claim and Claim Adjustment Expense Unearned premiums SEC Schedule, 12-18, Supplemental Information, Property-Casualty Insurance Underwriters, Unearned Premium Net earned premiums SEC Schedule, 12-18, Supplemental Information, Property-Casualty Insurance Underwriters, Earned Premium Net investment income SEC Schedule, 12-18, Supplemental Information, Property-Casualty Insurance Underwriters, Net Investment Income Prior year Amortization of policy acquisition costs SEC Schedule, 12-18, Supplemental Information, Property-Casualty Insurance Underwriters, Amortization of Deferred Policy Acquisition Cost Paid losses and loss adjustment expenses, net of reinsurance SEC Schedule, 12-18, Supplemental Information, Property-Casualty Insurance Underwriters, Paid Claim and Claim Adjustment Expense Net written premiums SEC Schedule, 12-18, Supplemental Information, Property-Casualty Insurance Underwriters, Premium Written Shares Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward] Unvested, beginning of year (in shares) Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number Granted (in shares) 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 Unvested, end of year (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] Unvested, 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) 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 Unvested, end of year (in dollars per share) Junior Subordinated Debt Junior Subordinated Debt [Axis] Junior Subordinated Debt [Axis] Represents information by junior subordinated debt types. Junior Subordinated Debt [Domain] Junior Subordinated Debt [Domain] Represents categorization of information by junior subordinated debt. James River Capital Trust I James River Capital Trust I [Member] Represents information about James River Capital Trust I. James River Capital Trust II James River Capital Trust Ii [Member] Represents information about James River Capital Trust II. James River Capital Trust III James River Capital Trust Iii [Member] Represents information about James River Capital Trust III. James River Capital Trust IV James River Capital Trust Iv [Member] Represents information about James River Capital Trust IV. Franklin Holdings II (Bermuda) Capital Trust I Franklin Holdings Ii Bermuda Capital Trust I [Member] Represents information about Franklin Holdings II Bermuda Capital Trust I. Issue date Debt Instrument, Issuance Date Principal amount of Trust Preferred Securities Face Value Of Trust Preferred Securities Represents face value of trust preferred securities. Principal amount of Junior Subordinated Debt Carrying amount of Junior Subordinated Debt net of repurchases Maturity date of Junior Subordinated Debt, unless accelerated earlier Debt Instrument, Maturity Date Trust common stock Trust Common Stock Represents trust common stock. Interest rate, per annum Debt Instrument, Description of Variable Rate Basis Junior Subordinated Debt Subordinated Borrowings Disclosure [Text Block]