Liability for Claims and Claims Adjustment Expense [Abstract] 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. Earnings Per Share [Abstract] Net income to shareholders Net Income (Loss) Attributable to Parent Weighted average common shares outstanding: 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 (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 (in dollars per share) Earnings Per Share, Diluted Investments [Abstract] Investment Income [Table] Investment Income [Table] Range [Axis] Range [Axis] Range [Domain] Range [Domain] Minimum Minimum [Member] Maximum Maximum [Member] Segments [Axis] Segments [Axis] Segments [Domain] Segments [Domain] Corporate and other Corporate and Other [Member] Excess and Surplus Lines Excess And Surplus Lines [Member] Represents information regarding excess and surplus lines segment. Major Types of Debt and Equity Securities [Axis] Major Types of Debt and Equity Securities [Axis] Major Types of Debt and Equity Securities [Domain] Major Types of Debt and Equity Securities [Domain] 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 bridge financing notes 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] 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. Total other invested assets Other Investments Investment income Investment Income, Net Ownership percentage Equity Method Investment, Ownership Percentage Cash distributions from LLCs Proceeds from Equity Method Investment, Dividends or Distributions Rate of interest Investment Interest Rate Interest income Investment Income, Interest Carrying values of limited partnerships held Carrying Values Of Limited Partnerships Held Represents carrying values of limited partnerships held across segments. Investment income (loss) 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 private subordinated notes Payments To Acquire Private Subordinated Debt Represents payments to acquire private subordinated debt. Schedule of Antidilutive Securities Excluded from Computation of Earnings Per Share [Table] Schedule of Antidilutive Securities Excluded from Computation of Earnings Per Share [Table] Antidilutive Securities [Axis] Antidilutive Securities [Axis] Antidilutive Securities, Name [Domain] Antidilutive Securities, Name [Domain] Stock options and restricted share units ("RSU's") Stock Options And Restricted Stock Units Rsu [Member] Stock options and share instrument which is convertible to stock or an equivalent amount of cash, after a specified period of time or when specified performance conditions are met. Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items] Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items] Number of securities excluded from the calculations of diluted earnings per share Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount Stockholders' Equity Note [Abstract] 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 Accounting Policies [Abstract] New Accounting Pronouncements or Change in Accounting Principle [Table] New Accounting Pronouncements or Change in Accounting Principle [Table] Equity Components [Axis] Equity Components [Axis] Equity Component [Domain] Equity Component [Domain] Retained Earnings Retained Earnings [Member] Adjustments for New Accounting Pronouncements [Axis] Adjustments for New Accounting Pronouncements [Axis] Type of Adoption [Domain] Type of Adoption [Domain] ASU 2016-01 Accounting Standards Update 2016-01 [Member] Accounting Standards Update 2016-01 [Member] ASU 2018-02 Accounting Standards Update 2018-02 [Member] Accounting Standards Update 2018-02 [Member] New Accounting Pronouncements or Change in Accounting Principle [Line Items] New Accounting Pronouncements or Change in Accounting Principle [Line Items] Number of insurance companies based in the United States Number Of Insurance Companies This element represents number of insurance companies owned by the entity. Investment in variable interest entities Variable Interest Entity, Reporting Entity Involvement, Maximum Loss Exposure, Amount Effective U.S. federal income tax expense rate Effective Income Tax Rate Reconciliation, Percent Percentage of available for sale securities Percentage Of Available For Sale Securities Represents percentage of available for sale securities. Cumulative effect of adoption of ASU Cumulative Effect of New Accounting Principle in Period of Adoption Net income Reduction in basic and diluted earnings per share Earnings Per Share, Basic and Diluted Schedule of Gain (Loss) on Investments [Table] Schedule of Gain (Loss) on Investments [Table] 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] BBB- or better Standard & Poor's, BBB- Rating [Member] Fixed maturity securities Debt Securities [Member] Puerto Rico loan Puerto Rico Loan [Member] Represents information about Puerto Rico Loan. Oil and gas companies loan Loan To Oil And Gas Companies [Member] Represents information about loan to oil and gas companies. Non-energy sector loan Non Energy Sector Loan [Member] Represents non-energy sector loan. Gain (Loss) on Investments [Line Items] Gain (Loss) on Investments [Line Items] Number of available-for-sale securities held in an unrealized loss position Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions Total fair value of unrealized loss position securities Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value Total gross unrealized losses of unrealized loss position securities Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss Fair value Available-for-sale Securities Aggregate net unrealized gain (loss) Available-for-sale Securities, Gross Unrealized Gain (Loss) Impairment loss Other than Temporary Impairment Losses, Investments, Available-for-sale Securities Unpaid principal on impaired loans Impaired Financing Receivable, Unpaid Principal Balance Carrying value of loan Loans Receivable, Net Allowance for credit losses on impaired loans Impaired Financing Receivable, Related Allowance Number of loans Number Of Loan Represents total number of loans. Bank loan participations gross unrealized losses Bank Loan Participations Gross Unrealized Losses Represents unrealized losses on bank loan participations. Number of impaired loans held Number Of Impaired Loans Represents the number of impaired loans. Carrying value of impaired loans Loan And Advances Carrying Value Represents the carrying value of impaired loans. Average recorded investment in impaired bank loans Impaired Financing Receivable, Average Recorded Investment Investment income during period loans were impaired Impaired Financing Receivable Interest Income Represents amount of impaired financing receivable, interest income. Net trading gains (losses) still held Trading Securities, Change in Unrealized Holding Gain (Loss) Carrying value of collateralized loan obligation held Carrying Value Of Collateralized Loan Obligation Held Represents carrying value of carrying value of collateralized loan obligation held. Net realized investment (losses) gains Realized Investment Gains (Losses) Investment in certificate of deposit Investment In Certificate Of Deposit Represents investment in certificate of deposit. Schedule of Available-for-sale Securities [Table] Schedule of Available-for-sale Securities [Table] 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] Schedule of Available-for-sale Securities [Line Items] Schedule of Available-for-sale Securities [Line Items] Less Than 12 Months, Fair Value Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value Less Than 12 Months, Gross Unrealized Losses Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss 12 Months or More, Fair Value Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value 12 Months or More, Gross Unrealized Losses Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss Total, Fair Value Total, Gross Unrealized Losses Accounting Policies Basis of Presentation and Significant Accounting Policies [Text Block] Dividend declared per share (in dollars per share) Common Stock, Dividends, Per Share, Declared Total Amount Dividends, Common Stock, Cash Fair Value Disclosures [Abstract] Fair Value, by Balance Sheet Grouping [Table] Fair Value, by Balance Sheet Grouping [Table] Measurement Frequency [Axis] Measurement Frequency [Axis] Fair Value, Measurement Frequency [Domain] Fair Value, Measurement Frequency [Domain] Recurring basis Fair Value, Measurements, Recurring [Member] Fair Value, Hierarchy [Axis] Fair Value, Hierarchy [Axis] Fair Value Hierarchy [Domain] Fair Value Hierarchy [Domain] 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] Preferred stock Preferred Stock [Member] Common stock Common Stock [Member] Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] Trading securities: Trading Securities [Abstract] Fixed maturity securities Trading Securities, Debt Short-term investments Short-term Investments Other Operating Expenses And Other Expenses [Abstract] Other Operating Expenses and Other Expenses Other Operating Expenses And Other Expenses [Text Block] Represents entire disclosure of Other operating expenses and other expenses. Goodwill and Intangible Assets Disclosure [Abstract] Schedule Of Acquired Intangible Assets [Table] Schedule Of Acquired Intangible Assets [Table] Represents the tabular information related to intangible assets acquired in the acquisition. 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. 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] 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) Life (Years) Finite-Lived Intangible Asset, Useful Life Earnings Per Share Earnings Per Share [Text Block] Subsequent Events [Abstract] Subsequent Events Subsequent Events [Text Block] Schedule of Share-based Compensation Arrangements by Share-based Payment Award [Table] Schedule of Share-based Compensation Arrangements by Share-based Payment Award [Table] 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] Award Type [Axis] Award Type [Axis] Equity Award [Domain] Equity Award [Domain] RSUs Restricted Stock Units (RSUs) [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, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward] Unvested, beginning of period (in shares) Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number Granted (in shares) Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period Vested (in shares) Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Vested in Period Forfeited (in shares) Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Forfeited in Period Unvested, end of period (in shares) Shares 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 period (in dollars per share) Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value Granted (in dollars per share) Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period, Weighted Average Grant Date Fair Value Vested (in dollars per share) Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Vested in Period, Weighted Average Grant Date Fair Value Forfeited (in dollars per share) Share-based Compensation Arrangements by Share-based Payment Award, Options, Forfeitures in Period, Weighted Average Exercise Price Unvested, end of period (in dollars per share) Vesting period (in years) Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Period Segment Reporting [Abstract] Schedule of Segment Reporting Information, by Segment [Table] Schedule of Segment Reporting Information, by Segment [Table] Consolidation Items [Axis] Consolidation Items [Axis] Consolidation Items [Domain] Consolidation Items [Domain] Reportable segments Operating Segments [Member] Specialty Admitted Insurance Specialty Admitted Insurance [Member] Represents information regarding specialty admitted insurance. Casualty Reinsurance Casualty Reinsurance [Member] Represents information regarding casualty reinsurance. Segment Reporting Information [Line Items] Segment Reporting Information [Line Items] Total underwriting profit of insurance segments Underwriting Profit Loss Of Operating Segments This element represents amount of underwriting Profit (loss) of operating segments. Other operating expenses of the Corporate and Other segment Other Operating Expenses Of Corporate And Other Segment Represents Other operating expenses of the Corporate and Other segment. Underwriting profit Underwriting Profit Represents amount of underwriting profit. Net investment income Net Investment Income Amortization of intangible assets Amortization of Intangible Assets Other income and expenses Other Income And Expenses Represents other income and expenses. Interest expense Interest Expense Income before taxes Income (Loss) from Continuing Operations before Income Taxes, Noncontrolling Interest Statement of Financial Position [Abstract] Assets Assets [Abstract] Invested assets: Fixed maturity securities: Marketable Securities, Fixed Maturities [Abstract] Available-for-sale, at fair value (amortized cost: 2018 – $1,054,902; 2017 – $1,008,662) Available-for-sale Securities, Debt Securities Trading, at fair value (amortized cost: 2018 – $3,800; 2017 – $3,801) Equity securities available-for-sale, at fair value (cost: 2018 – $80,464; 2017 – $75,318) Available-for-sale Securities, Equity Securities Bank loan participations held-for-investment, at amortized cost, net of allowance Other invested assets Total invested assets Investments Cash and cash equivalents Cash and Cash Equivalents, at Carrying Value 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 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 Senior debt Long-term Debt Junior subordinated debt Junior Subordinated Debenture Owed to Unconsolidated Subsidiary Trust Accrued expenses Accrued Liabilities Other liabilities Other Liabilities Total liabilities Liabilities Commitments and contingent liabilities Commitments and Contingencies Shareholders’ equity: Stockholders' Equity Attributable to Parent [Abstract] Common Shares – 2018 and 2017: $0.0002 par value; 200,000,000 shares authorized; 29,866,705 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 Fair Value Measurements Fair Value Disclosures [Text Block] Commitments and Contingencies Disclosure [Abstract] Contingent Liabilities [Table] Contingent Liabilities [Table] Discloses information about contingent liabilities. Investment, Name [Axis] Investment, Name [Axis] Investment, Name [Domain] Investment, Name [Domain] Third-party Reinsureds Third-party Reinsureds [Member] Third-party Reinsureds [Member] Legal Entity [Axis] Legal Entity [Axis] Entity [Domain] Entity [Domain] JRG Reinsurance Company, Ltd. Jrg Reinsurance Company Ltd [Member] Represents reinsurance subsidiary of the entity. James River Insurance Co James River Insurance Co [Member] James River Insurance Co [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. Letter of credit 102.5 Million Letter Of Credit 102.5 Million [Member] Represents letter of credit facility 102.5 million. Letter of credit 100 Million one Letter Of Credit 100 Million One [Member] Letter Of Credit 100 Million One [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. Letters of credit facility, amount Letter Of Credit Facility Amount Represents amount of letter of credit facility. Amount of letters of credit issued Letters of Credit Outstanding, Amount 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 Reserve For Losses And Loss Adjustment Expenses [Table] Reserve For Losses And Loss Adjustment Expenses [Table] A table or schedule providing information pertaining to reserve for losses and Loss adjustment expenses. Favorable Reserve Development [Axis] Favorable Reserve Development [Axis] Information about favorable reserve development. Favorable Reserve Development [Domain] Favorable Reserve Development [Domain] Information about favorable reserve development. Prior accident years Prior Accident Years [Member] Represents information about prior accident years . Accident Year [Axis] Accident Year [Axis] Represents information about accident year. Accident Year [Domain] Accident Year [Domain] Represents information about accident year. From accident years 2016 and 2014 Accident Years From 2016 And 2014 [Member] Represents Information about favorable reserve development from 2016 and 2014 accident years. From accident years 2015, 2014 and prior accident years Accident Years 2015, 2014, and Prior [Member] Accident Years 2015, 2014, and Prior [Member] From the 2014-2016 accident years Accident Years 2016, 2015, and 2014 [Member] Accident Years 2016, 2015, and 2014 [Member] Reserve For Losses And Loss Adjustment Expenses [Line Items] Reserve For Losses And Loss Adjustment Expenses [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. Favorable development on prior year loss reserves Development On Prior Year Loss Reserves [Abstract] Reserve for losses and loss adjustment expenses Prior Year Claims and Claims Adjustment Expense Statement of Cash Flows [Abstract] Operating activities Net Cash Provided by (Used in) Operating Activities, Continuing Operations [Abstract] 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: Available-for-sale Securities [Abstract] Purchases – fixed maturity securities Payments to Acquire Available-for-sale Securities, Debt Sales – fixed maturity securities Proceeds from Sale of Available-for-sale Securities, Debt Maturities and calls – fixed maturity securities Proceeds from Maturities, Prepayments and Calls of Available-for-sale Securities Purchases – equity securities Payments to Acquire Available-for-sale Securities, Equity Sales – equity securities Proceeds from Sale of Available-for-sale Securities, Equity 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 Short-term investments, net Payments for (Proceeds from) Short-term Investments Securities receivable or payable, net Payments for (Proceeds from) Investments Purchases of property and equipment Payments to Acquire Property, Plant, and Equipment Net cash used in investing activities Net Cash Provided by (Used in) Investing Activities Financing activities Net Cash Provided by (Used in) Financing Activities, Continuing Operations [Abstract] Dividends paid Payments of Dividends Issuance 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 Repayments of financing obligations net of proceeds Repayments of Lines of Credit 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 period Cash and cash equivalents at end of period Supplemental information Supplemental Cash Flow Information [Abstract] Interest paid Interest Paid Schedule of dividends Schedule of Dividends Payable [Table Text Block] Schedule of summary of option activity Schedule of Share-based Compensation, Stock Options, Activity [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] 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] 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 Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value [Table Text Block] Schedule of summary of realized gains and losses Realized 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. 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] Assets Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract] Available-for-sale: Fixed maturity securities Equity securities Trading: Fixed maturity securities Trading Securities 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] Capital Stock and Equity Awards Stockholders' Equity Note Disclosure [Text Block] Goodwill and Intangible Assets Goodwill and Intangible Assets Disclosure [Text Block] Other Comprehensive Income (Loss), Net of Tax [Abstract] Unrealized (losses) gains arising during the period, before U.S. income taxes Other Comprehensive Income (Loss), Unrealized Holding Gain (Loss) on Securities Arising During Period, before Tax U.S. income taxes Other Comprehensive Income (Loss), Unrealized Holding Gain (Loss) on Securities Arising During Period, Tax Unrealized (losses) gains arising during the period, net of U.S. income taxes Other Comprehensive Income (Loss), Unrealized Holding Gain (Loss) on Securities Arising During Period, Net of Tax Less reclassification adjustment: Other Comprehensive Income (Loss), Available-for-sale Securities Adjustment, before Reclassification Adjustments, Net of Tax [Abstract] Net realized investment (losses) gains Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI for Sale of Securities, before Tax U.S. income tax expenses 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 Other Comprehensive Income (Loss), Net of Tax Amortization of policy acquisition costs Deferred Policy Acquisition Cost, Amortization Expense Other underwriting expenses of the operating segments Other Underwriting Expense Other operating expenses of the Corporate and Other segment Total Other Cost and Expense, Operating Subsequent Event [Table] Subsequent Event [Table] Subsequent Event Type [Axis] Subsequent Event Type [Axis] Subsequent Event Type [Domain] Subsequent Event Type [Domain] Subsequent event Subsequent Event [Member] Subsequent Event [Line Items] Subsequent Event [Line Items] Dividends payable, date declared Dividends Payable, Date Declared Cash dividend declared (in dollars per share) Dividends Payable, Amount Per Share Dividends payable, date to be paid Dividends Payable, Date to be Paid Dividend payable, record date Dividends Payable, Date of Record Investments Investment [Text Block] Schedule of components of comprehensive income Comprehensive Income (Loss) [Table Text Block] Plan Name [Axis] Plan Name [Axis] Plan Name [Domain] Plan Name [Domain] 2014 LTIP Long Term Incentive Plan 2014 [Member] Represents information regarding Long Term Incentive Plan 2014. 2014 Director Plan Non Employee Director Incentive Plan 2014 [Member] Represents information regarding 2014 Non Employee Director Incentive Plan. Non-qualified stock options Employee Stock Option [Member] 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 Contingent Liabilities Commitments and Contingencies 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 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] Corporate and Other Corporate, Non-Segment [Member] Gross written premiums Premiums Written, Gross Net earned premiums Premiums Earned, Net Underwriting profit (loss) of insurance segments Net investment income Interest expense Segment revenues Revenues Segment goodwill Segment assets Segment Information Segment Reporting Disclosure [Text Block] Fair Value Inputs, Assets, Quantitative Information [Table] Fair Value Inputs, Assets, Quantitative Information [Table] Valuation Technique [Axis] Valuation Technique [Axis] Valuation Technique [Domain] Valuation Technique [Domain] Market approach Market Approach Valuation Technique [Member] Level 3 Fair Value Inputs, Assets, Quantitative Information [Line Items] Fair Value Inputs, Assets, Quantitative Information [Line Items] Available-for-sale securities 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. Income Statement [Abstract] Tax on net unrealized gains (losses) Other Comprehensive Income (Loss), Available-for-sale Securities, Tax Options Number of common shares issued during period Stock Issued During Period, Shares, New Issues Common stock, shares outstanding Common Stock, Shares, Outstanding Restricted stock unit dividend equivalents Restricted Stock Unit Dividend Equivalents Represents amount of dividend equivalent of RSU's. Dividends payable Dividends Payable Shares Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding [Roll Forward] Beginning of period (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 period (in shares) Exercisable, end of period (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 period (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 End of period (in dollars per share) Exercisable, end of period (in dollars per share) Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercisable, Weighted Average Exercise Price Equity [Abstract] 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 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 Cost or Amortized Cost Available-for-sale Securities, Debt Maturities, Amortized Cost Basis, Fiscal Year Maturity [Abstract] One year or less Available-for-sale Securities, Debt Maturities, Next Twelve Months, Amortized Cost Basis After one year through five years Available-for-sale Securities, Debt Maturities, Year Two Through Five, Amortized Cost Basis After five years through ten years Available-for-sale Securities, Debt Maturities, Year Six Through Ten, Amortized Cost Basis After ten years Available-for-sale Securities, Debt Maturities, after Ten Years, Amortized Cost Basis 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. Total Available-for-sale Debt Securities, Amortized Cost Basis Fair Value Available-for-sale Securities, Debt Maturities, Fair Value, Fiscal Year Maturity [Abstract] One year or less Available-for-sale Securities, Debt Maturities, Next Twelve Months, Fair Value After one year through five years Available-for-sale Securities, Debt Maturities, Year Two Through Five, Fair Value After five years through ten years Available-for-sale Securities, Debt Maturities, Year Six Through Ten, Fair Value After ten years Available-for-sale Securities, Debt Maturities, after Ten 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 Statement of Stockholders' Equity [Abstract] Statement [Table] Statement [Table] Common Shares Additional Paid-in Capital Additional Paid-in Capital [Member] Accumulated Other Comprehensive 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] Balance (in shares) Balance Net income Other comprehensive income Dividends Dividends Exercised (in shares) Exercise of stock options Stock Issued During Period, Value, Stock Options Exercised Vesting of RSUs (in shares) Stock Issued During Period, Shares, Restricted Stock Award, Net of Forfeitures Vesting of RSUs Stock Issued During Period, Value, Restricted Stock Award, Net of Forfeitures Compensation expense under share incentive plans Adjustments to Additional Paid in Capital, Share-based Compensation, Requisite Service Period Recognition Balance (in shares) Balance Revenues Revenues [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 Net realized and unrealized (losses) gains on investments Other income Other Income Total revenues Expenses Operating Expenses [Abstract] Losses and loss adjustment expenses Liability for Unpaid Claims and Claims Adjustment Expense, Incurred Claims Other operating expenses Other expenses Other Operating Income (Expense), Net Amortization of intangible assets Total expenses Operating Expenses Income tax expense Income Tax Expense (Benefit) Net income Other comprehensive (loss) income: Net unrealized (losses) gains, net of taxes of $(544) in 2018 and $1,514 in 2017 Total comprehensive (loss) income Comprehensive Income (Loss), Net of Tax, Attributable to Parent Per share data: Earnings Per Share, Basic and Diluted [Abstract] Basic earnings per share (in dollars per share) Diluted earnings per share (in dollars per share) Weighted-average common shares outstanding: Weighted Average Number of Shares Outstanding, Basic [Abstract] Diluted (in shares) Schedule of gross carrying amounts and accumulated amortization Schedule of Intangible Assets and Goodwill [Table Text Block] Schedule of Business Acquisitions, by Acquisition [Table] Schedule of Business Acquisitions, by Acquisition [Table] Business Acquisition [Axis] Business Acquisition [Axis] Business Acquisition, Acquiree [Domain] Business Acquisition, Acquiree [Domain] 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 Business Acquisition, Percentage of Voting Interests Acquired Schedule of summary of company's segment results Schedule of Segment Reporting Information, by Segment [Table Text Block] Schedule of underwriting profit 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] Number of reportable segments Number of Reportable Segments Fee income in Excess and Surplus Lines segment Fee Income Represents amount of fee income . Basis of Presentation Basis of Accounting, Policy [Policy Text Block] Estimates and Assumptions Use of Estimates, Policy [Policy Text Block] Variable Interest Entities Consolidation, Variable Interest Entity, Policy [Policy Text Block] Income Tax Expense Income Tax, Policy [Policy Text Block] Adopted Accounting Standards New Accounting Pronouncements, Policy [Policy Text Block] Prospective Accounting Standards Description of New Accounting Pronouncements Not yet Adopted [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 other operating expenses Schedule of Other Operating Cost and Expense, by Component [Table Text Block] Bank loan participations Bank Loan Obligations [Member] Short-term investments and other Short Term Investments And Other [Member] Represents investments which are not otherwise included in another category or item that the entity has the intent to sell or dispose of within one year from the date of the balance sheet. Gross realized gains Available-for-sale Securities, Gross Realized Gains Gross realized losses Available-for-sale Securities, Gross Realized Losses Gross realized gains Bank Loan Participations Gross Realized Gains Represents the gross realized gains on bank loan participations. Gross realized losses Bank Loan Participations Gross Realized Losses Represents the gross realized losses on bank loan participations. 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. Changes in fair values of equity securities Equity Securities, Changes in Fair Value Equity Securities, Changes in Fair Value 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. Net realized investment gains Fair Value Measurements, Recurring and Nonrecurring [Table] Fair Value Measurements, Recurring and Nonrecurring [Table] Nonrecurring basis Fair Value, Measurements, Nonrecurring [Member] Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] Bank loan participations held-for-investment Available-for-sale debt securities, amortized cost Trading securities, debt, amortized cost Trading Securities, Debt, Amortized Cost Available-for-sale equity securities, amortized cost 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 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 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 Liability for Unpaid Claims and Claims Adjustment Expense, Net 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 Reserve for losses and loss adjustment expenses gross of reinsurance recoverables on unpaid losses and loss adjustment expenses at end of period Cost or Amortized Cost Available-for-sale Securities, Amortized Cost Basis Gross Unrealized Gains Available-for-sale Securities, Accumulated Gross Unrealized Gain, before Tax Gross Unrealized Losses Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax Fair Value Other Comprehensive Income Comprehensive Income (Loss) Note [Text Block] Document And Entity Information [Abstract] Entity Registrant Name Entity Registrant Name Entity Central Index Key Entity Central Index Key Trading Symbol Trading Symbol Current Fiscal Year End Date Current Fiscal Year End Date Entity Filer Category Entity Filer Category Entity Common Stock, Shares Outstanding Entity Common Stock, Shares Outstanding 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