Organization, Consolidation and Presentation of Financial Statements [Abstract] Schedule of other liabilities Other Liabilities [Table Text Block] Insurance [Abstract] Summary of reserve for losses and loss adjustment expenses Schedule of Liability for Unpaid Claims and Claims Adjustment Expense [Table Text Block] Equity [Abstract] Share-based compensation expense Share-based Payment Arrangement, Expense Related tax benefits Share-based Payment Arrangement, Expense, Tax Benefit Investments, Debt and Equity Securities [Abstract] Schedule of available-for-sale fixed maturities Schedule of Available-for-sale Securities Reconciliation [Table Text Block] Schedule of available-for-sale securities by contractual maturity Investments Classified by Contractual Maturity Date [Table Text Block] Schedule of investments held in an unrealized loss position Debt Securities, Available-for-sale, Unrealized Loss Position, Fair Value [Table Text Block] Schedule of other information regarding available-for-sale securities Debt Securities, Available-for-sale [Table Text Block] Schedule of net investment income Investment Income [Table Text Block] Schedule of investment in unconsolidated subsidiaries Schedule Of Investments In Unconsolidated Subsidiaries [Table Text Block] Schedule Of Investments In Unconsolidated Subsidiaries [Table Text Block] Schedule of losses and tax credits related to tax credit partnership investments Equity Method Investments [Table Text Block] Schedule of net realized investment gains (losses) Gain (Loss) on Securities [Table Text Block] Schedule of OTTI recorded in OCI Other than Temporary Impairment, Credit Losses Recognized in Earnings [Table Text Block] Fair Value Disclosures [Abstract] Fair Value Measurement Inputs and Valuation Techniques [Table] Fair Value Measurement Inputs and Valuation Techniques [Table] Financial Instrument [Axis] Financial Instrument [Axis] Financial Instruments [Domain] Financial Instruments [Domain] Corporate debt, limited observable inputs Corporate Debt, Limited Observable Inputs [Member] Corporate Debt, Limited Observable Inputs [Member] Other commercial mortgage-backed securities Commercial Mortgage Backed Securities [Member] Other asset-backed securities Other Asset-Backed Securities [Member] Other Asset-Backed Securities [Member] Other investments Other Investments [Member] Fair Value Hierarchy and NAV [Axis] Fair Value Hierarchy and NAV [Axis] Fair Value, Measurements, Fair Value Hierarchy [Domain] Fair Value Hierarchy and NAV [Domain] Level 3 Fair Value, Inputs, Level 3 [Member] Measurement Input Type [Axis] Measurement Input Type [Axis] Measurement Input Type [Domain] Measurement Input Type [Domain] Measurement input, comparability adjustment Measurement Input, Comparability Adjustment [Member] Valuation Approach and Technique [Axis] Valuation Approach and Technique [Axis] Valuation Approach and Technique [Domain] Valuation Approach and Technique [Domain] Market Comparable Securities Valuation, Market Approach [Member] Discounted Cash Flows Valuation, Income Approach [Member] Statistical Measurement [Axis] Statistical Measurement [Axis] Statistical Measurement [Domain] Statistical Measurement [Domain] Minimum Minimum [Member] Maximum Maximum [Member] Weighted average Weighted Average [Member] Fair Value Measurement Inputs and Valuation Techniques [Line Items] Fair Value Measurement Inputs and Valuation Techniques [Line Items] Assets: Assets, Fair Value Disclosure [Abstract] AFS debt securities Debt Securities, Available-for-sale Assets measured at fair value Assets, Fair Value Disclosure Available-for-sale, measurement input Debt Securities, Available-for-sale, Measurement Input Other assets, measurement input Other Investments, Measurement Input Other Investments, Measurement Input Segment Reporting [Abstract] Segment Information Segment Reporting Disclosure [Text Block] Income Tax Disclosure [Abstract] Income taxes receivable Income Taxes Receivable Unrecognized tax benefits Unrecognized Tax Benefits Accrued liability for interest related to unrecognized tax benefits Unrecognized Tax Benefits, Interest on Income Taxes Accrued Schedule of Investment Income, Reported Amounts, by Category [Table] Investment Income [Table] Schedule of Investment Income, Reported Amounts, by Category [Axis] Investment Type [Axis] Investments [Domain] Investments [Domain] Fixed maturities Debt Securities [Member] Equities Equity Securities [Member] Short-term investments, including Other Short-term investments and Other invested assets [Member] Short-term investments and Other invested assets [Member] BOLI Cash Surrender Value [Member] Schedule of Investment Income, Reported Amounts, by Category [Line Items] Net Investment Income [Line Items] Net Investment Income Net Investment Income [Abstract] Investment Income Interest and Dividend Income, Operating Investment fees and expenses Investment Income, Investment Expense Net investment income Net Investment Income Statement of Financial Position [Abstract] Available for sale securities, amortized cost Debt Securities, Available-for-sale, Amortized Cost Trading securities, cost Trading Securities, Cost Equity Investments, fair value, cost Equity Securities, FV-NI, Cost Other investments, portion carried at fair value Other Investments, Fair Value Disclosure Other Investments, Fair Value Disclosure Common shares, par value (in usd per share) Common Stock, Par or Stated Value Per Share Common shares, shares authorized (in shares) Common Stock, Shares Authorized Common shares, shares issued (in shares) Common Stock, Shares, Issued Deferred tax expense (benefit) on accumulated other comprehensive income (loss) AOCI Tax, Attributable to Parent Treasury shares, number of shares (in shares) Treasury Stock, Shares Schedule of Segment Reporting Information, by Segment [Table] Schedule of Segment Reporting Information, by Segment [Table] Segments [Axis] Segments [Axis] Segments [Domain] Segments [Domain] Workers' Compensation Insurance Workers' Compensation Insurance [Member] Syndicate 1729 Syndicate 1729 [Member] Syndicate 1729 [Member] Syndicate 6131 Syndicate 6131 [Member] Syndicate 6131 [Member] Segment Reporting Information [Line Items] Segment Reporting Information [Line Items] Worker's compensation SPC percentage ceded Alternative Market Solutions Percentage Ceded Alternative Market Solutions Percentage Ceded Proportion of capital provided to support Lloyd's Syndicate 1729 Proportion Of Capital Provided To Support Segment This item represents the capital provided in support of a segment by a corporate member as a percentage of total capital provided by all members to support the segment. Commitments and Contingencies Disclosure [Abstract] Other Commitments [Table] Other Commitments [Table] Other Commitments [Axis] Other Commitments [Axis] Other Commitments [Domain] Other Commitments [Domain] Commitment to provide capital Commitment to Provide Capital [Member] Commitment to Provide Capital [Member] Funding Commitments Funding Commitments [Member] Funding Commitments [Member] Lloyd's Syndicates Lloyd's Syndicates [Member] Lloyd's Syndicates [Member] Category of Item Purchased [Axis] Category of Item Purchased [Axis] Long-term Purchase Commitment, Category of Item Purchased [Domain] Long-term Purchase Commitment, Category of Item Purchased [Domain] Data analytics and services Data Analytics Services [Member] Data Analytics Services [Member] Other Commitments [Line Items] Other Commitments [Line Items] Commitments total Other Commitment Required FAL deposit Deposit Assets Current lending capacity under revolving credit agreement Syndicate Credit Agreement, Current Lending Capacity Amount of current lending capacity under the Syndicate credit agreement without considering any amounts currently outstanding under the facility. Interest rate on revolving credit agreement (percent) Syndicate Credit Agreement, Interest Rate Syndicate Credit Agreement, Interest Rate on Lendings Repayments of Short-term Debt Repayments (Advances) Under Syndicate Credit Agreement Repayments (Advances) Under Syndicate Credit Agreement Unused commitments to extend credit Unused Commitments to Extend Credit Purchase commitment, period (in years) Long-term Purchase Commitment, Period Annual fee Purchase Obligation, Due in Next Twelve Months Operating expense Operating Expenses Purchase obligation Purchase Obligation Derivative Instruments and Hedging Activities Disclosure [Abstract] Derivatives Derivative Instruments and Hedging Activities Disclosure [Text Block] Leases [Abstract] Lessee, Lease, Description [Table] Lessee, Lease, Description [Table] Lessee, Lease, Description [Line Items] Lessee, Lease, Description [Line Items] Lease term Lessee, Operating Lease, Term of Contract Renewal term Lessee, Operating Lease, Renewal Term Excluded lease payments Lessee, Operating Lease, Liability, Lease Not Yet Commenced, Amount Lessee, Operating Lease, Liability, Lease Not Yet Commenced, Amount Lease term, not yet commenced Lessee, Operating Lease, Lease Not yet Commenced, Term of Contract New Accounting Pronouncements or Change in Accounting Principle [Table] New Accounting Pronouncements or Change in Accounting Principle [Table] Adjustments for New Accounting Pronouncements [Axis] Adjustments for New Accounting Pronouncements [Axis] Type of Adoption [Domain] Type of Adoption [Domain] Accounting Standards Update 2018-07 Accounting Standards Update 2018-07 [Member] New Accounting Pronouncements or Change in Accounting Principle [Line Items] New Accounting Pronouncements or Change in Accounting Principle [Line Items] Number of reportable segments (in segments) Number of Reportable Segments Operating lease ROU assets Operating Lease, Right-of-Use Asset Operating lease liabilities Operating Lease, Liability Retained earnings Retained Earnings (Accumulated Deficit) Schedule of Credit Derivatives [Table] Schedule of Credit Derivatives [Table] Credit Rating Source [Axis] Credit Rating Source [Axis] Credit Rating Source [Domain] Credit Rating Source [Domain] NRSRO Nationally Recognized Statistical Rating Organization (NRSRO) [Member] Nationally Recognized Statistical Rating Organization (NRSRO) [Member] Internal Credit Assessment [Axis] Internal Credit Assessment [Axis] Internal Credit Assessment [Domain] Internal Credit Assessment [Domain] NRSRO, Rating AA Minus Nationally Recognized Statistical Rating Organization (NRSRO), Rating AAminus [Member] Nationally Recognized Statistical Rating Organization (NRSRO), Rating AAminus [Member] NRSRO, Rating BBB Plus Nationally Recognized Statistical Rating Organization (NRSRO), Rating BBBplus [Member] Nationally Recognized Statistical Rating Organization (NRSRO), Rating BBBplus [Member] NRSRO, Rating A Minus Nationally Recognized Statistical Rating Organization (NRSRO), Rating A Minus [Member] Nationally Recognized Statistical Rating Organization (NRSRO), Rating A Minus [Member] NRSRO, Rating AAA Nationally Recognized Statistical Rating Organization (NRSRO), Rating AAA [Member] Nationally Recognized Statistical Rating Organization (NRSRO), Rating AAA [Member] Measurement Frequency [Axis] Measurement Frequency [Axis] Measurement Frequency [Domain] Measurement Frequency [Domain] Fair Value, Measurements, Nonrecurring Fair Value, Nonrecurring [Member] Credit Derivatives [Line Items] Credit Derivatives [Line Items] Credit rating Concentration Risk, Percentage Fair value, net asset (liability) Fair Value, Net Asset (Liability) Fair value of funded deferred compensation assets Deferred Compensation Plan Assets Separate line of credit agreements (in agreements) Line of Credit, Number of Agreement Line of Credit, Number of Agreement SPC dividends payable Segregated Portfolio Cell Dividends Payable The cumulative undistributed earnings of segregated portfolio cells that are contractually payable to external preferred shareholders of the cells Unpaid shareholder dividends Dividends Payable All other Other Liabilities Not Detailed Other Liabilities Not Detailed Total other liabilities Other Liabilities Leases Lessee, Operating Leases [Text Block] Basis of Presentation Organization, Consolidation and Presentation of Financial Statements Disclosure [Text Block] 2019 Lessee, Operating Lease, Liability, Payments, Remainder of Fiscal Year 2020 Lessee, Operating Lease, Liability, Payments, Due Year Two 2021 Lessee, Operating Lease, Liability, Payments, Due Year Three 2022 Lessee, Operating Lease, Liability, Payments, Due Year Four 2023 Lessee, Operating Lease, Liability, Payments, Due Year Five Thereafter Lessee, Operating Lease, Liability, Payments, Due after Year Five Total future minimum lease payments Lessee, Operating Lease, Liability, Payments, Due Less: Imputed interest Lessee, Operating Lease, Liability, Undiscounted Excess Amount Total operating lease liabilities Right-of-use assets obtained in exchange for new operating lease liabilities Operating Lease, Payments Weighted-average remaining lease term (in years) Operating Lease, Weighted Average Remaining Lease Term Weighted-average discount rate Operating Lease, Weighted Average Discount Rate, Percent Losses recorded Income (Loss) from Affordable Housing Projects, Equity Method Investments Tax credits recognized Affordable Housing Tax Credits and Other Tax Benefits, Amount Losses recorded Income (Loss) from Historical Projects, Equity Method Investments Income (Loss) from Historical Projects, Equity Method Investments Tax credits recognized Historic Tax Credits Investments and Other Tax Benefits, Amount Historic Tax Credits Investments and Other Tax Benefits, Amount Variable Interest Entities [Abstract] Variable interest entities. Schedule of Variable Interest Entities [Table] Schedule of Variable Interest Entities [Table] Variable Interest Entities by Classification of Entity [Axis] Variable Interest Entities [Axis] Variable Interest Entity, Classification [Domain] Variable Interest Entity, Classification [Domain] Variable interest entity, not primary beneficiary Variable Interest Entity, Not Primary Beneficiary [Member] Balance Sheet Location [Axis] Balance Sheet Location [Axis] Balance Sheet Location [Domain] Balance Sheet Location [Domain] Equity investments Investments In Unconsolidated Subsidiaries [Member] Investments In Unconsolidated Subsidiaries [Member] Variable Interest Entity [Line Items] Variable Interest Entity [Line Items] VIE interests carrying value Variable Interest Entity, Nonconsolidated, Carrying Amount, Assets Schedule of interest rate caps Schedule of Interest Rate Derivatives [Table Text Block] Specialty P&C Specialty Property and Casualty [Member] Specialty Property and Casualty [Member] Traditional business Traditional Business [Member] Traditional Business [Member] Alternative market business Alternative Market Business [Member] Alternative Market Business [Member] Segregated Portfolio Cell Reinsurance Segregated Portfolio Cell Reinsurance [Member] Segregated Portfolio Cell Reinsurance [Member] Product and Service [Axis] Product and Service [Axis] Product and Service [Domain] Product and Service [Domain] Healthcare professional liability Healthcare Professional Liability [Member] Healthcare Professional Liability [Member] Legal professional liability Legal Professional Liability [Member] Legal Professional Liability [Member] Medical technology liability Medical Technology and Life Sciences Product Liability [Member] Medical Technology and Life Sciences Product Liability [Member] Other Other Premiums [Member] Other Premiums [Member] Workers' compensation Workers' Compensation Alternative Market Business [Member] Activity associated with our Alternative Market Business of our Workers' Compensation segment. Gross premiums earned Gross Premiums Earned Amount of premiums earned before premiums ceded to other entities, including directed and assumed premiums earned. Ceded premiums earned Ceded Premiums Earned Segment net premiums earned Premiums Earned, Net Premiums assumed under Quota Share Agreement Premiums Assumed Under Quota Share Agreement Premiums Assumed Under Quota Share Agreement Variable Interest Entities Variable Interest Entity Disclosure [Text Block] Debt Disclosure [Abstract] Schedule of outstanding debt Schedule of Long-term Debt Instruments [Table Text Block] Schedule of Lease Cost Lease, Cost [Table Text Block] Schedule of Lease Liability Lessee, Operating Lease, Liability, Maturity [Table Text Block] Liability for Claims and Claims Adjustment Expense [Table] Liability for Claims and Claims Adjustment Expense [Table] Retroactive Insurance Contract Retroactive Insurance Contract [Member] Retroactive Insurance Contract [Member] Liability for Claims and Claims Adjustment Expense [Line Items] Liability for Claims and Claims Adjustment Expense [Line Items] Minimum period for claims resolution (years) Minimum Period For Claims Resolution Minimum Period For Claims Resolution Number of business partitions (in partitions) Number of Business Partitions Number of Business Partitions Summary of reserve for losses and loss adjustment expenses Liability for Unpaid Claims and Claims Adjustment Expense, Period Increase (Decrease) [Abstract] Balance, beginning of year Liability for Claims and Claims Adjustment Expense Less reinsurance recoverables on unpaid losses and loss adjustment expenses Reinsurance Recoverable for Unpaid Claims and Claims Adjustments Net balance, beginning of year Liability for Unpaid Claims and Claims Adjustment Expense, Net Net losses: Liability for Unpaid Claims and Claims Adjustment Expense, Incurred Claims [Abstract] Current year Current Year Claims and Claims Adjustment Expense Favorable development of reserves established in prior years, net Prior Year Claims and Claims Adjustment Expense Total Liability for Unpaid Claims and Claims Adjustment Expense, Incurred Claims Paid related to: 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 paid Liability for Unpaid Claims and Claims Adjustment Expense, Claims Paid Net balance, end of period Plus reinsurance recoverables on unpaid losses and loss adjustment expenses Balance, end of period Liabilities for Guarantees on Long-Duration Contracts [Table] Liabilities for Guarantees on Long-Duration Contracts [Table] Retroactive Insurance Contract, Prospective Coverage Retroactive Insurance Contract, Prospective Coverage [Member] Retroactive Insurance Contract, Prospective Coverage [Member] Retroactive Insurance Contract, Retroactive Coverage Retroactive Insurance Contract, Retroactive Coverage [Member] Retroactive Insurance Contract, Retrospective Coverage [Member] Liabilities for Guarantees on Long-Duration Contracts [Line Items] Liabilities for Guarantees on Long-Duration Contracts [Line Items] Net premiums earned Current Year Claims and Claims Adjustment Expense Net losses and loss adjustment expenses Policyholder Benefits and Claims Incurred, Net Reserve for losses and loss adjustment expenses Cover page. Document Type Document Type Document Quarterly Report Document Quarterly Report Document Period End Date Document Period End Date Document Transition Report Document Transition Report Entity File Number Entity File Number Entity Registrant Name Entity Registrant Name Entity Incorporation, State or Country Code Entity Incorporation, State or Country Code Entity Tax Identification Number Entity Tax Identification Number Entity Address, Address Line One Entity Address, Address Line One Entity Address, City or Town Entity Address, City or Town Entity Address, State or Province Entity Address, State or Province Entity Address, Postal Zip Code Entity Address, Postal Zip Code City Area Code City Area Code Local Phone Number Local Phone Number Title of 12(b) Security Title of 12(b) Security Trading Symbol Trading Symbol Security Exchange Name Security Exchange Name Entity Current Reporting Status Entity Current Reporting Status Entity Interactive Data Current Entity Interactive Data Current Entity Filer Category Entity Filer Category Entity Small Business Entity Small Business Entity Emerging Growth Company Entity Emerging Growth Company Entity Shell Company Entity Shell Company Entity Common Stock, Shares Outstanding Entity Common Stock, Shares Outstanding Entity Central Index Key Entity Central Index Key Current Fiscal Year End Date Current Fiscal Year End Date Document Fiscal Year Focus Document Fiscal Year Focus Document Fiscal Period Focus Document Fiscal Period Focus Amendment Flag Amendment Flag 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] Award Type [Domain] Award Type [Domain] Restricted Share Units (in shares) Restricted Stock Units (RSUs) [Member] Performance Share Units (in shares) Performance Shares [Member] Level at which performance shares were granted in 2016 Performance Shares Granted in 2016 [Member] Performance Shares Granted in 2016 [Member] Equity Components [Axis] Equity Components [Axis] Equity Component [Domain] Equity Component [Domain] Accumulated Other Comprehensive Income (Loss) AOCI Attributable to Parent [Member] Retained Earnings Retained Earnings [Member] Share-based Compensation Arrangement by Share-based Payment Award [Line Items] Share-based Compensation Arrangement by Share-based Payment Award [Line Items] Authorized common stock (in shares) Authorized preferred stock (in shares) Preferred Stock, Shares Authorized Quarterly dividend declared, per share (in usd per share) Common Stock, Dividends, Per Share, Declared Dividend declared Dividends, Common Stock, Cash Total authorizations which remain available for use Stock Repurchase Or Debt Repayment Remaining Authorized Amount The remaining amount authorized by an entity's Board of Directors for stock repurchase or debt repayment. Common shares acquired (in shares) Treasury Stock, Shares, Acquired Awards in period (in shares) Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period Fair value of each unit awarded (in usd 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 Award vesting period Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Period Award payout rate Share Based Compensation Arrangement By Share Based Payment Award Payout Rate Share based compensation arrangement by share based payment award payout rate. Shares issued in period for share-based compensation (in shares) Share-based Compensation Arrangement by Share-based Payment Award, Shares Issued in Period Bonus compensation shares issued (in shares) Bonus Compensation Shares Issued Bonus compensation shares issued. Non-credit loss, net of tax Accumulated Other Comprehensive Income (Loss), Other than Temporary Impairment, Not Credit Loss, Net of Tax, Available-for-sale, Debt Securities Reclassification from AOCI to retained earnings for stranded tax effects Tax Cuts And Jobs Act Of 2017 Reclassification From AOCI To Retained Earnings Tax Cuts And Jobs Act Of 2017 Reclassification From Aoci To Retained Earnings Schedule of fair value of assets Schedule of Fair Value, Assets and Liabilities Measured on Recurring Basis [Table Text Block] Schedule of quantitative information regarding level 3 valuations Fair Value Measurement Inputs and Valuation Techniques [Table Text Block] Schedule of fair value measurements - level 3 assets Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Table Text Block] Schedule of investments in LLCs and limited partnerships Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Table Text Block] Schedule of financial instruments not measured at fair value Fair Value, by Balance Sheet Grouping [Table Text Block] Reserve for Losses and Loss Adjustment Expenses Liability for Future Policy Benefits and Unpaid Claims Disclosure [Text Block] Earnings Per Share [Abstract] Schedule of earnings per share, basic and diluted Schedule of Earnings Per Share, Basic and Diluted [Table Text Block] Purchase Match Units (in shares) Employee Purchase Plan [Member] Employee Purchase Plan Weighted average number of common shares outstanding, basic (in shares) Weighted Average Number of Shares Outstanding, Basic Dilutive securities (in shares) Incremental Common Shares Attributable to Dilutive Effect of Share-based Payment Arrangements Weighted average number of common shares outstanding, diluted (in shares) Weighted Average Number of Shares Outstanding, Diluted Effect of dilutive shares on earnings per share (in usd per share) Income (Loss) from Continuing Operations, Per Diluted Share Antidilutive shares excluded from computation of earnings per share (in shares) Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount Marketable Securities [Table] Marketable Securities [Table] Corporate Debt Corporate Debt Securities [Member] Marketable Securities [Line Items] Marketable Securities [Line Items] Total OTTI losses: Other than Temporary Impairment Losses, Investments Portion of OTTI losses recognized in other comprehensive income before taxes Other than Temporary Impairment Losses, Investments, Portion in Other Comprehensive Loss, before Tax, Portion Attributable to Parent Net impairment losses recognized in earnings Other-than-temporary Impairment Loss, Debt Securities, Portion Recognized in Earnings Gross realized gains, available-for-sale fixed maturities Debt Securities, Available-for-sale, Realized Gain Gross realized (losses), available-for-sale fixed maturities Debt Securities, Available-for-sale, Realized Loss Net realized gains (losses), trading fixed maturities Debt Securities, Trading, Realized Gain (Loss) Net realized gains (losses), equity investments Equity Securities, FV-NI, Realized Gain Net realized gains (losses), other investments Other Investments, Realized Gain (Loss) This item represents the gain (loss) realized during the period from the sale of Other Investments. Change in unrealized holding gains (losses), trading fixed maturities Debt Securities, Trading, Unrealized Gain (Loss) Change in unrealized holding gains (losses), equity investments Trading Securities, Change in Unrealized Holding Gain (Loss) Change in unrealized holding gains (losses), convertible securities, carried at fair value Unrealized Gain (Loss) on Hybrid Instrument, Net Other Gain (Loss) on Sale of Other Investments Total net realized investment gains (losses) Gain (Loss) on Investments Consolidation Items [Axis] Consolidation Items [Axis] Consolidation Items [Domain] Consolidation Items [Domain] Operating segments Operating Segments [Member] Inter-segment Eliminations Intersegment Eliminations [Member] Corporate Corporate Segment [Member] Net investment income Equity in earnings (loss) of unconsolidated subsidiaries Income (Loss) from Equity Method Investments Net realized gains (losses) Other income (expense) Other Income Net losses and loss adjustment expenses Underwriting, policy acquisition and operating expenses Underwriting Policy Acquisition And Operating Expense Underwriting, policy acquisition and operating expense. Segregated portfolio cells dividend expense (income) Segregated Portfolio Cells Dividend Expense (Income) Segregated Portfolio Cells Dividend Expense (Income) Interest expense Interest Expense Income tax benefit (expense) Income Tax Expense (Benefit) Net income Net Income (Loss) Attributable to Parent Depreciation and amortization, net of accretion Depreciation, Depletion and Amortization Information regarding sales and purchases of available-for-sale securities Schedule of Sales And Purchases Of Available For Sale Securities [Abstract] Schedule of Sales And Purchases Of Available For Sale Securities [Abstract] Proceeds from sales (exclusive of maturities and paydowns) Proceeds from Sale of Debt Securities, Available-for-sale Purchases Payments to Acquire Debt Securities, Available-for-sale Assets Assets [Abstract] Investments Investments [Abstract] Fixed maturities, available for sale, at fair value; amortized cost, $2,188,547 and $2,116,825, respectively Fixed maturities, trading, at fair value; cost, $42,905 and $38,445, respectively Debt Securities, Trading Equity investments, at fair value; cost, $398,489 and $450,931, respectively Equity Securities, FV-NI Short-term investments Other Short-term Investments Business owned life insurance Life Insurance, Corporate or Bank Owned, Amount Investment in unconsolidated subsidiaries Investment In Unconsolidated Subsidiaries Investment In Unconsolidated Subsidiaries Other investments, $33,824 and $31,344 at fair value, respectively, otherwise at cost or amortized cost Other Investments Total Investments Investments Cash and cash equivalents Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents Premiums receivable Premiums Receivable, Net Receivable from reinsurers on paid losses and loss adjustment expenses Reinsurance Recoverable for Paid Claims and Claims Adjustments Receivable from reinsurers on unpaid losses and loss adjustment expenses Prepaid reinsurance premiums Prepaid Reinsurance Premiums Deferred policy acquisition costs Deferred Policy Acquisition Cost Deferred tax asset, net Deferred Income Tax Assets, Net Real estate, net Property, Plant and Equipment, Net Intangible assets, net Other Intangible Assets, Net Goodwill Goodwill Other assets Other Assets Total Assets Assets Liabilities and Shareholders' Equity Liabilities and Equity [Abstract] Liabilities Liabilities [Abstract] Policy liabilities and accruals Policy liabilities and accruals [Abstract] Policy liabilities and accruals. Unearned premiums Unearned Premiums Reinsurance premiums payable Reinsurance Payable Total Policy Liabilities Policy Liabilities Total policy liabilities. Other liabilities Debt less debt issuance costs Long-term Debt Total Liabilities Liabilities Shareholders' Equity Stockholders' Equity Attributable to Parent [Abstract] Common shares, par value $0.01 per share, 100,000,000 shares authorized, 63,112,288 and 62,989,421 shares issued, respectively Common Stock, Value, Issued Additional paid-in capital Additional Paid in Capital, Common Stock Accumulated other comprehensive income (loss), net of deferred tax expense (benefit) of $8,627 and ($4,355), respectively Accumulated Other Comprehensive Income (Loss), Net of Tax Treasury shares, at cost, 9,352,373 shares as of each respective period end Treasury Stock, Value Total Shareholders' Equity Stockholders' Equity Attributable to Parent Total Liabilities and Shareholders' Equity Liabilities and Equity Debt Long-term Debt [Text Block] Basis of Presentation Basis of Accounting, Policy [Policy Text Block] Reclassifications Reclassification, Policy [Policy Text Block] Leases Lessee, Leases [Policy Text Block] Accounting Changes Adopted and Not Yet Adopted New Accounting Pronouncements, Policy [Policy Text Block] Fair Value Measurement Fair Value Measurement, Policy [Policy Text Block] Statement of Stockholders' Equity [Abstract] Statement [Table] Statement [Table] Equity Components [Axis] Common Stock Common Stock [Member] Additional Paid-in Capital Additional Paid-in Capital [Member] Treasury Stock Treasury Stock [Member] Accounting Standards Update 2016-01 Accounting Standards Update 2016-01 [Member] Accounting Standards Update 2018-02 Accounting Standards Update 2018-02 [Member] Statement [Line Items] Statement [Line Items] Increase (Decrease) in Stockholders' Equity: Increase (Decrease) in Stockholders' Equity [Roll Forward] Beginning balance Cumulative-effect adjustment adoption of ASU Cumulative Effect of New Accounting Principle in Period of Adoption Common shares issued for compensation and effect of shares reissued to stock purchase plan Stock Issued During Period, Value, Other Share-based compensation APIC, Share-based Payment Arrangement, Increase for Cost Recognition Net effect of restricted and performance shares issued Shares Issued, Value, Share-based Payment Arrangement, after Forfeiture Dividends to shareholders Dividends, Common Stock Other comprehensive income (loss) Other Comprehensive Income (Loss), Net of Tax Net income Ending balance Schedule of Equity Method Investments [Table] Schedule of Equity Method Investments [Table] Investment, Name [Axis] Investment, Name [Axis] Investment, Name [Domain] Investment, Name [Domain] Qualified affordable housing project tax credit partnerships Qualified Affordable Housing Tax Credit Partnerships [Member] Qualified Affordable Housing Tax Credit Partnerships [Member] Other tax credit partnerships Other Tax Credit Partnerships [Member] Other Tax Credit Partnerships [Member] All other investments, primarily investment fund LPs/LLCs Other Limited Partnerships and Limited Liability Company [Member] Other Limited Partnerships and Limited Liability Company [Member] Schedule of Equity Method Investments [Line Items] Schedule of Equity Method Investments [Line Items] Unconsolidated Subsidiaries Investments in and Advance to Affiliates, Subsidiaries, Associates, and Joint Ventures [Abstract] Investment in unconsolidated subsidiaries Schedule of Long-term Debt Instruments [Table] Schedule of Long-term Debt Instruments [Table] Long-term Debt, Type [Axis] Long-term Debt, Type [Axis] Long-term Debt, Type [Domain] Long-term Debt, Type [Domain] Senior notes due 2023 Senior Notes [Member] Revolving credit agreement Line of Credit [Member] Mortgage loans Mortgages [Member] Debt Instrument [Axis] Debt Instrument [Axis] Debt Instrument, Name [Domain] Debt Instrument, Name [Domain] Senior notes due 2023 Senior notes due 2023 [Member] Senior notes due 2023 [Member] Revolving credit agreement Revolving Credit Facility [Member] Variable Rate [Axis] Variable Rate [Axis] Variable Rate [Domain] Variable Rate [Domain] LIBOR London Interbank Offered Rate (LIBOR) [Member] Debt Instrument [Line Items] Debt Instrument [Line Items] Gross debt Long-term Debt, Gross Less debt issuance costs Unamortized Debt Issuance Expense Debt less debt issuance costs Stated interest rate on debt Debt Instrument, Interest Rate, Stated Percentage Line of credit maximum borrowing capacity Line of Credit Facility, Maximum Borrowing Capacity Effective interest rate on debt Debt Instrument, Interest Rate, Effective Percentage Basis spread on variable rate for debt Debt Instrument, Basis Spread on Variable Rate Shareholders' Equity Stockholders' Equity Note Disclosure [Text Block] Earnings Per Share Earnings Per Share [Text Block] Schedule of Available-for-sale Securities [Table] Schedule of Available-for-sale Securities [Table] Realized investment gains (losses) AOCI, Accumulated Gain (Loss), Debt Securities, Available-for-sale, Parent [Member] Reclassifications from AOCI to net income: Debt Securities, Available-for-sale [Line Items] Reclassifications from AOCI to net income: Reclassification from Accumulated Other Comprehensive Income, Current Period, before Tax Tax effect, calculated using the 21% federal statutory tax rate Reclassification from AOCI, Current Period, Tax Net reclassification adjustments Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax Deferred tax expense (benefit) included in OCI Other Comprehensive Income (Loss), Tax Retroactive Insurance Contracts Insurance Disclosure [Text Block] Schedule of share-based compensation expense and related tax benefits Share-based Payment Arrangement, Cost by Plan [Table Text Block] Schedule of reclassification adjustments related to available-for-sale securities Reclassification out of Accumulated Other Comprehensive Income [Table Text Block] Debt Securities, Available-for-sale [Table] Debt Securities, Available-for-sale [Table] U.S. Treasury obligations US Treasury Securities [Member] U.S. Government-sponsored enterprise obligations US Government-sponsored Enterprises Debt Securities [Member] State and municipal bonds US States and Political Subdivisions Debt Securities [Member] Corporate debt Residential mortgage-backed securities Residential Mortgage Backed Securities [Member] Agency commercial mortgage-backed securities Government National Mortgage Association Certificates and Obligations (GNMA) [Member] Other asset-backed securities Asset-backed Securities, Securitized Loans and Receivables [Member] 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 Estimated Fair Value Derivative [Table] Derivative [Table] Derivative Instrument [Axis] Derivative Instrument [Axis] Derivative Contract [Domain] Derivative Contract [Domain] Interest Rate Cap Interest Rate Cap [Member] Income Statement Location [Axis] Income Statement Location [Axis] Interest expense Income Statement Location [Domain] Interest expense Interest Expense [Member] Derivative [Line Items] Derivative [Line Items] Gains (Losses) Recognized in Income on Derivatives Derivative, Gain (Loss) on Derivative, Net Other than Temporary Impairment, Credit Losses Recognized in Earnings: Other than Temporary Impairment, Credit Losses Recognized in Earnings [Roll Forward] Balance beginning of period Other than Temporary Impairment, Credit Losses Recognized in Earnings, Credit Losses on Debt Securities Held No OTTI has been previously recognized Other than Temporary Impairment, Credit Losses Recognized in Earnings, Additions, No Previous Impairment Balance ending of period Fair Value Measurement Fair Value Disclosures [Text Block] Other assets Other Assets [Member] Premium paid on derivative for right to receive cash payments Debt Instrument, Unamortized Premium Derivative asset, notional amount Derivative Asset, Notional Amount Floor interest rate on derivative Derivative, Floor Interest Rate Cap interest rate on derivative Derivative, Cap Interest Rate Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Table] Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Table] Investment Type [Axis] Mortgage fund Mortgage Fund [Member] Mortgage Fund [Member] Private debt funds Private Debt Funds [Member] Private Debt Funds [Member] Long equity fund Private Equity Funds, Non-US [Member] Long/short equity funds Long/Short Equity Funds [Member] Long/Short Equity Funds [Member] Non-public equity funds Private Equity Funds [Member] Multi-strategy fund of funds Multi-Strategy Fund of Funds [Member] Investment LPs/LLCs that are structured to build and manage low volatility, multi-manager portfolios that have little or no correlation to broader fixed income and equity security markets. Credit fund Structured Credit Fund [Member] Investment LPs/LLCs that seek to obtain superior risk-adjusted absolute returns by acquiring and actively managing a diversified portfolio of debt securities, including bonds, loans and other asset-backed instruments. Long/short commodities fund Long/Short Commodity Fund [Member] Long/Short Commodity Fund Strategy focused fund Strategy Focused Fund [Member] Strategy Focused Fund [Member] Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items] Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items] Unfunded Commitments Fair Value, Investments, Entities that Calculate Net Asset Value Per Share, Unfunded Commitments Fair Value Alternative Investment Statement of Cash Flows [Abstract] Operating Activities Net Cash Provided by (Used in) Operating Activities [Abstract] 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] Depreciation and amortization, net of accretion Depreciation, Amortization and Accretion, Net (Increase) decrease in cash surrender value of BOLI Life Insurance, Corporate or Bank Owned, Change in Value Net realized investment (gains) losses Share-based compensation Share-based Payment Arrangement, Noncash Expense Deferred income tax expense (benefit) Deferred Income Tax Expense (Benefit) Policy acquisition costs, net of amortization (net deferral) Increase (Decrease) in Deferred Policy Acquisition Costs Equity in (earnings) loss of unconsolidated subsidiaries Equity In Earnings (Loss) Of Unconsolidated Subsidiaries Equity In Earnings (Loss) Of Unconsolidated Subsidiaries Distributed earnings from unconsolidated subsidiaries Return On Invested Capital From Unconsolidated Subsidiaries Return On Invested Capital From Unconsolidated Subsidiaries Other Other Noncash Income (Expense) Other changes in assets and liabilities: Increase (Decrease) in Operating Capital [Abstract] Premiums receivable Increase (Decrease) in Premiums Receivable Reinsurance related assets and liabilities Increase (Decrease) In Reinsurance Related Assets And Liabilities The change in reinsurance related assets and liabilities on the balance sheet. Other assets Increase (Decrease) in Other Operating Assets 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 Other liabilities Increase (Decrease) in Other Operating Liabilities Net cash provided (used) by operating activities Net Cash Provided by (Used in) Operating Activities Investing Activities Net Cash Provided by (Used in) Investing Activities [Abstract] Purchases of: Payments to Acquire Investments [Abstract] Fixed maturities, available for sale Fixed maturities, trading Payments to Acquire Trading Securities Held-for-investment Equity investments Payments To Acquire Equity Securities, FV-NI Payments To Acquire Equity Securities, FV-NI Other investments Payments to Acquire Other Investments Funding of qualified affordable housing project tax credit partnerships Payments For Funding Of Tax Credit Limited Partnerships Payments for funding of tax credit limited partnerships. Investment in unconsolidated subsidiaries Payments For (Proceeds From) Investment In Unconsolidated Subsidiaries The cash outflow associated with an entity's investment in equity method investments. Proceeds from sales or maturities of: Proceeds from Sale, Maturity and Collection of Investments [Abstract] Fixed maturities, available for sale Proceeds from Sale and Maturity of Debt Securities, Available-for-sale Equity investments Proceeds from Sale and Maturity of Debt and Equity Securities, FV-NI, Held-for-investment Other investments Proceeds from Sale and Maturity of Other Investments Return of invested capital from unconsolidated subsidiaries Proceeds from Equity Method Investment, Distribution, Return of Capital Net sales or maturities (purchases) of short-term investments Payments for (Proceeds from) Short-term Investments Unsettled security transactions, net change Unsettled security transactions net Unsettled security transactions, net. Purchases of capital assets Payments to Acquire Productive Assets Repayments (advances) under Syndicate Credit Agreement Other Payments for (Proceeds from) Other Investing Activities Net cash provided (used) by investing activities Net Cash Provided by (Used in) Investing Activities Financing Activities Net Cash Provided by (Used in) Financing Activities [Abstract] Repayments under Revolving Credit Agreement Repayments of Lines of Credit Repayments of Mortgage Loans Repayments of Secured Debt Dividends to shareholders Payments of Ordinary Dividends, Common Stock Capital contribution received from (return of capital to) external segregated portfolio cell participants External Capital Contribution Received (Return Of Capital) For Segregated Portfolio Cells External Capital Contribution Received (Return Of Capital) For Segregated Portfolio Cells Other Proceeds from (Payments for) Other Financing Activities Net cash provided (used) by financing activities Net Cash Provided by (Used in) Financing Activities Increase (decrease) in cash and cash equivalents Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents, Period Increase (Decrease), Including Exchange Rate Effect Cash and cash equivalents at beginning of period Cash and cash equivalents at end of period Significant Non-Cash Transactions Significant Non Cash Transactions Abstract Significant non cash transactions. Dividends declared and not yet paid Operating ROU assets obtained in exchange for operating lease liabilities Right-of-Use Asset Obtained in Exchange for Operating Lease Liability Commitments and Contingencies Commitments and Contingencies Disclosure [Text Block] Secured debt fund Investment redemption notice period Fair Value, Investments, Entities that Calculate Net Asset Value Per Share, Investment Redemption, Notice Period Payment period for redemption of LP valued at NAV Payment period for redemption of LP valued at NAV The number of days required for payment upon redemption of a particular LP that is valued at NAV. Liquidating investments remaining period Fair Value, Investments, Entities that Calculate Net Asset Value Per Share, Liquidating Investment, Remaining Period Redemption percentage of LP at NAV for which initial payment is limited Redemption Percentage of LP at NAV above which initial payment is limited The redemption percentage of a particular LP valued at NAV above which initial payment is limited. Investment redemption notice period, two funds Fair Value, Investments, Entities that Calculate Net Asset Value, Investment Redemption, Notice Period, Two Funds Fair Value, Investments, Entities that Calculate Net Asset Value, Investment Redemption, Notice Period, Two Funds Investment redemption notice period, one fund Fair Value, Investments, Entities that Calculate Net Asset Value, Investment Redemption, Notice Period, One Fund Fair Value, Investments, Entities that Calculate Net Asset Value, Investment Redemption, Notice Period, One Fund Statement of Comprehensive Income [Abstract] Revenues Revenues [Abstract] Net premiums earned Net investment income Equity in earnings (loss) of unconsolidated subsidiaries Net realized investment gains (losses): Realized Investment Gains (Losses) [Abstract] OTTI losses Net impairment losses recognized in earnings Other net realized investment gains (losses) Other Net Realized Investment Gain (Loss) Other net realized investment gains (losses). Other income Total revenues Revenues Expenses Operating Expenses [Abstract] Underwriting, policy acquisition and operating expenses Underwriting, Policy Acquisition And Operating Expenses [Abstract] Underwriting, Policy Acquisition And Operating Expenses [Abstract] DPAC amortization Deferred Policy Acquisition Costs, Amortization Expense Interest expense Total expenses Benefits, Losses and Expenses Income before income taxes Income (Loss) from Continuing Operations before Income Taxes, Noncontrolling Interest Provision for income taxes Income Tax Expense (Benefit), Continuing Operations [Abstract] Current expense (benefit) Current Income Tax Expense (Benefit) Deferred expense (benefit) Total income tax expense (benefit) Other comprehensive income (loss), after tax, net of reclassification adjustments Comprehensive income (loss) Comprehensive Income (Loss), Net of Tax, Attributable to Parent Earnings per share Basic (in usd per share) Earnings Per Share, Basic Diluted (in usd per share) Earnings Per Share, Diluted Weighted average number of common shares outstanding: Weighted Average Number of Shares Outstanding Reconciliation [Abstract] Basic (in shares) Diluted (in shares) Cash dividends declared per common share (in usd per share) U.S. Government-sponsored enterprise obligations Other commercial mortgage-backed securities Other asset-backed securities Amortized Cost Due in one year or less Debt Securities, Available-for-sale, Maturity, Allocated and Single Maturity Date, Rolling within One Year, Fair Value Due after one year through five years Debt Securities, Available-for-sale, Maturity, Allocated and Single Maturity Date, Rolling after One Through Five Years, Fair Value Due after five years through ten years Debt Securities, Available-for-sale, Maturity, Allocated and Single Maturity Date, Rolling after Five Through Ten Years, Fair Value Due after ten years Debt Securities, Available-for-sale, Maturity, Allocated and Single Maturity Date, Rolling after 10 Years, Fair Value Total Fair Value Number of instruments (in derivative instruments) Number of Interest Rate Derivatives Held Notional amount Estimated fair value Derivative Asset Investments Investments in Debt and Marketable Equity Securities (and Certain Trading Assets) Disclosure [Text Block] U.S. Treasury obligations Fair value Investments continuous unrealized loss position [Abstract] Investments Continuous Unrealized Loss Position. Fair Value Debt Securities, Available-for-sale, Unrealized Loss Position Less than 12 Months, Fair Value Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months More than 12 Months, Fair Value Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer Unrealized Loss Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss [Abstract] Unrealized Loss Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss Less than 12 Months, Unrealized Loss Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss More than 12 Months, Unrealized Loss Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss Short-term investments Short-term Investments [Member] Non government-backed Non Government-Backed [Member] Securities that are not backed by the U.S. government or U.S. government agencies. Tax Credit Partnerships Almost 100% Ownership Tax Credit Partnerships Almost 100% Ownership [Member] Tax Credit Partnerships with Almost a 100% Ownership Percentage [Member] Tax Credit Partnerships Less Than 20% Ownership Tax Credit Partnerships Less Than 20% Ownership [Member] Tax Credit Partnerships Less Than 20% Ownership [Member] Other Limited Partnerships and Limited Liability Company, Greater Than 25% Ownership Other Limited Partnerships and Limited Liability Company, Greater Than 25 Percent Ownership [Member] Other Limited Partnerships and Limited Liability Company, Greater Than 25 Percent Ownership [Member] Other Limited Partnerships and Limited Liability Company Less than 25% Ownership Other Limited Partnerships and Limited Liability Company Less than 25 Percent Ownership [Member] Other Limited Partnerships and Limited Liability Company Less than 25 Percent Ownership [Member] Securities on deposit with state insurance departments Assets Held by Insurance Regulators Debt securities in unrealized loss position (in securities) Debt Securities, Available-for-sale, Unrealized Loss Position, Number of Positions Debt securities in unrealized loss position as percentage of total debt securities held Number Of Debt Securities In Unrealized Loss Position As Percentage Of Debt Securities Number of debt securities in unrealized loss position as percentage of total debt securities. Issuers in unrealized loss position (in issuers) Available For Sale Securities In Unrealized Loss Positions Number Of Issuers Available For Sale Securities In Unrealized Loss Positions. Single greatest unrealized loss position Single Greatest Unrealized Loss Position Single greatest unrealized loss position. Second greatest unrealized loss position Second Greatest Unrealized Loss Position Second greatest unrealized loss position. Business owned life insurance cost Business Owned Life Insurance Cost Business Owned Life Insurance Cost. Number of tax credit partnerships almost 100% ownership percentage Number of Tax Credit Partnerships Almost 100% Ownership Percentage Number of Tax Credit Partnerships Almost 100% Ownership Percentage Investment ownership percentage Investment In Unconsolidated Subsidiaries, Ownership Percentage Investment In Unconsolidated Subsidiaries, Ownership Percentage Number of LPs / LLCs with investment ownership percent over 25% (in businesses) Number of LPs / LLCs with Equity Method Investment Ownership Percentage Over 25 percent Number of LPs / LLCs with Equity Method Investment Ownership Percentage Over 25 percent Income Taxes Income Tax Disclosure [Text Block] 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 [Member] 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] Financial instruments not measured at fair value Financial Instruments Not Measured At Fair Value [Abstract] Financial instruments not measured at fair value. Financial assets: Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract] Short-term and other investments Investments, Fair Value Disclosure Other assets Other Assets, Fair Value Disclosure Financial liabilities: Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract] Debt instruments Debt Instrument, Fair Value Disclosure Other liabilities Other Liabilities, Fair Value Disclosure Schedule of segment reporting information, by segment Schedule of Segment Reporting Information, by Segment [Table Text Block] Schedule of gross premiums by product Revenue from External Customers by Products and Services [Table Text Block] Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Table] Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Table] Asset-backed Securities Asset-backed Securities [Member] Net investment income Investment Income [Member] Net realized investment gains (losses) Gain (Loss) on Investments [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: Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward] Beginning balance Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Value Total gains (losses) realized and unrealized: Gains Losses Realized and Unrealized Assets [Abstract] Total gains (losses) realized and unrealized. Included in earnings, as a part of: Gains Losses By Earnings Category Assets [Abstract] Included in Earnings, as a part of. Total gains (losses) realized and unrealized, included in earnings Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Gain (Loss) Included in Earnings Included in other comprehensive income Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Gain (Loss) Included in Other Comprehensive Income (Loss) Purchases Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Purchases Sales Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Sales Transfers in Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Transfers Into Level 3 Transfers out Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Transfers out of Level 3 Ending balance Change in unrealized gains (losses) included in earnings for the above period for Level 3 assets held at period-end Fair Value, Asset, Recurring Basis, Still Held, Unrealized Gain (Loss) Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Table] Fair Value, Recurring and Nonrecurring [Table] Equity investments Investment in unconsolidated subsidiaries Recurring Fair Value, Recurring [Member] Corporate debt, multiple observable inputs Corporate Bonds Multiple Observable Inputs [Member] Debt securities that are issued by either a domestic or foreign corporate business entity with a promise of repayment and fair value has been determined using multiple observable inputs. Financial Equity Financial Securities [Member] Equity securities in financial sector. Utilities/Energy Utilities Energy Equity Securities [Member] Equity securities in the utilities and energy sectors. Consumer oriented Consumer Oriented [Member] Equity securities in consumer oriented sector. Industrial Equity Industrial Securities [Member] Equity securities in financial sector. Bond funds Fixed Income Funds [Member] All other All Other [Member] Equity securities in industry sectors that are not listed separately. Other investments Level 1 Fair Value, Inputs, Level 1 [Member] Level 2 Fair Value, Inputs, Level 2 [Member] Fair Value Measured at Net Asset Value Per Share Fair Value Measured at Net Asset Value Per Share [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] Fixed maturities, trading Equity investments Total assets categorized within the fair value hierarchy Assets carried at NAV, which approximates fair value and which are not categorized within the fair value hierarchy Total assets at fair value Assets, Fair Value Disclosure, Including NAV Value Not Within Fair Value Hierarchy Assets, Fair Value Disclosure, Including NAV Value Not Within Fair Value Hierarchy Operating lease expense Operating Lease, Expense Sublease income Sublease Income Net lease expense Lease, Cost Rental income from owned properties Rental Income, Owned Properties Rental Income, Owned Properties