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that Calculate Net Asset Value Per Share [Line Items] Change in unrealized gains (losses) included in earnings for the above period for Level 3 assets held at period-end Fair Value, Liability, Recurring Basis, Still Held, Unrealized Gain (Loss) Schedule of Share-based Compensation Arrangements by Share-based Payment Award [Table] Schedule of Share-Based Compensation Arrangements by Share-Based Payment Award [Table] Schedule of Activity for Restricted Share Units Share-Based Payment Arrangement, Restricted Stock and Restricted Stock Unit, Activity [Table Text Block] Adjustment to Non-PEO NEO Compensation Footnote Adjustment to Non-PEO NEO Compensation Footnote [Text Block] Other shares issued for compensation (in shares) Stock Issued During Period, Shares, Share-based Compensation, Other Stock Issued During Period, Shares, Share-based Compensation, Other Direct premiums earned Premiums earned Direct Premiums Earned Retirement Benefits [Abstract] Retirement Benefits [Abstract] 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Recognized Statistical Rating Organization N R S R O Rating A Minus [Member] Nationally Recognized Statistical Rating Organization N R S R O Rating A Minus Commitments and Contingencies Disclosure [Abstract] Commitments and Contingencies Disclosure [Abstract] Reinsurance premiums payable Reinsurance Payable Utilities/Energy Utilities Energy Equity Securities [Member] Equity securities in the utilities and energy sectors. 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Exercise Price Award Exercise Price Entity Filer Category Entity Filer Category Financial Equity Financial Securities [Member] Equity securities in financial sector. Benefits paid Defined Benefit Plan, Benefit Obligation, Benefits Paid Reserve for the future utilization of the DDR benefit Liability for Future Policy Benefits and Unpaid Claims and Claims Adjustment Expense U.S. federal statutory tax rate Effective Income Tax Rate Reconciliation, at Federal Statutory Income Tax Rate, Percent Estimated aggregate amortization of intangible assets for 2028 Finite-Lived Intangible Asset, Expected Amortization, Year Three SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Abstract] SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Abstract] Vesting [Domain] Vesting [Domain] Amortization of DPAC SEC Schedule, 12-16, Insurance Companies, Supplementary Insurance Information, Amortization of Deferred Policy Acquisition Cost Investment in unconsolidated subsidiaries Investment in unconsolidated subsidiaries Investment In Unconsolidated 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Transaction-related costs Effective Income Tax Rate Reconciliation, Transaction Related Costs, Percent Effective Income Tax Rate Reconciliation, Transaction Related Costs, Percent Local Phone Number Local Phone Number Additional 402(v) Disclosure Additional 402(v) Disclosure [Text Block] Percentage ownership Investment In Unconsolidated Subsidiaries, Ownership Percentage Investment In Unconsolidated Subsidiaries, Ownership Percentage Other Other Payment for (Proceeds from) Other Investing Activity Share-Based Payments Share-Based Payment Arrangement [Text Block] Assets Assets Assets [Abstract] Credit Facility [Axis] Credit Facility [Axis] Contribution Certificates Long-term Debt and Contribution Certificates, Fair Value Disclosure Long-term Debt and Contribution Certificates, Fair Value Disclosure Underlying Security Market Price Change Underlying Security Market Price Change, Percent Deferred policy acquisition costs SEC Schedule, 12-16, Insurance Companies, Supplementary Insurance Information, Deferred Policy Acquisition Cost Other Commitments [Axis] Other Commitments [Axis] Debt Instrument [Axis] Debt Instrument [Axis] Forfeited (in dollars per share) Share-Based Compensation Arrangement by Share-Based Payment Award, Equity Instruments Other than Options, Forfeitures, Weighted Average Grant Date Fair Value Benefit Plans Retirement Benefits [Text Block] Fair Value Measurement Fair Value Disclosures [Text Block] Credit Facility [Domain] Credit Facility [Domain] Shareholders' Equity Shareholders’ Equity: Equity, Attributable to Parent [Abstract] Vesting rights, percentage Share-Based Compensation Arrangement by Share-Based Payment Award, Award Vesting Rights, Percentage Common shares reacquired Treasury Stock, Value, Acquired, Cost Method Expected gains reclassified Interest Rate Cash Flow Hedge Gain (Loss) to be Reclassified During Next 12 Months, Net Total gains (losses) realized and unrealized: Gains Losses Realized and Unrealized Assets [Abstract] Total gains (losses) realized and unrealized. Interest rate (as percent) Debt Instrument, Interest Rate, Stated Percentage Investment, Name [Axis] Investment, Name [Axis] Schedule of Gross Premiums by Product Revenue from External Customers by Products and Services [Table Text Block] Entity Voluntary Filers Entity Voluntary Filers Other underwriting, policy acquisition and operating expenses SEC Schedule, 12-16, Insurance Companies, Supplementary Insurance Information, Other Operating Expense Other investments (at fair value, $1,215 and $2,077, respectively, otherwise at cost or amortized cost) Other Long-Term Investments Accident Year Short-Duration Insurance Contracts, Accident Year [Domain] Securities transferred at fair value as dividends from subsidiaries Securities transferred at fair value as dividends from subsidiaries The fair value of securities transferred to a parent company as dividends from its subsidiaries. Depreciation and amortization, net of accretion Depreciation, Amortization and Accretion, Net Entity Registrant Name Entity Registrant Name Anticipated time frame for distribution at the discretion of the LP (in years) Fair Value, Investments, Entities that Calculate Net Asset Value Per Share, Liquidating Investment, Remaining Period Stock Price or TSR Estimation Method Stock Price or TSR Estimation Method [Text Block] Total net periodic benefit cost (income) Defined Benefit Plan, Net Periodic Benefit Cost (Credit) Other investments, measurement input Alternative Investment, Measurement Input Summary of compensation expense and related tax benefit recognized during each period and compensation cost expense in future periods Share-Based Payment Arrangement, Additional Disclosure [Abstract] Net reserves acquired from acquisitions Liability for Unpaid Claims and Claims Adjustment Expense, Business Combination Unearned premium adjustment Deferred Tax Assets, Tax Deferred Expense, Reserves and Accruals, Unearned Premiums Reserve Other State and Local Tax Jurisdiction, Other [Member] Total assets categorized within the fair value hierarchy Assets, Fair Value Disclosure Impairment losses Total impairment losses: Impairment Losses, Investments Impairment Losses, Investments Debt securities in unrealized loss position (in securities) Debt Securities, Available-for-Sale, Unrealized Loss Position, Number of Positions Provision for expected credit losses Premium Receivable, Credit Loss Expense (Reversal) Number of operating segments Number of Operating Segments Tax Credit Carryforward [Line Items] Tax Credit Carryforward [Line Items] Equity investments Payments to Acquire Equity Securities, FV-NI Interest cost Interest cost Defined Benefit Plan, Interest Cost 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 Non-segmented items Segment Reporting, Reconciling Item, Excluding Corporate Nonsegment [Member] Operating expense Other Underwriting Expense Other changes recognized in OCI: Defined Benefit Plan, Accumulated Other Comprehensive (Income) Loss, before Tax [Abstract] Schedule of Amortizable Intangible Assets Schedule of Finite-Lived Intangible Assets [Table Text Block] Restatement Determination Date: Restatement Determination Date [Axis] Number of limited partners, redemption allowed with prior notice Number of Limited Partners, Redemption Allowed with Prior Notice Number of Limited Partners, Redemption Allowed with Prior Notice Net effect of restricted and performance shares issued Shares Issued, Value, Share-Based Payment Arrangement, after Forfeiture Number of reporting units Number of Reporting Units Schedule of Interest Rate Swaps Schedule of Interest Rate Derivatives [Table Text Block] Provision for income taxes: Income Tax Expense (Benefit), Continuing Operations [Abstract] Other Proceeds from (Payment for) Other Financing Activity Name Trading Arrangement, Individual Name Common shares issued for compensation Stock Issued During Period, Value, Other Principal amount Debt Instrument, Face Amount Statement of Comprehensive Income [Abstract] Statement of Comprehensive Income [Abstract] Defined Benefit Plan, Weighted Average Assumptions Used in Calculating Net Periodic Benefit Cost [Abstract] Defined Benefit Plan, Weighted Average Assumptions Used in Calculating Net Periodic Benefit Cost [Abstract] Name Awards Close in Time to MNPI Disclosures, Individual Name Beginning balance (in dollars per share) Ending balance (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 Other net investment gains (losses) Other Net Realized Investment Gain (Loss) Other net realized investment gains (losses). 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Schedule of Reconciliation of Unrecognized Tax Benefits Schedule of Unrecognized Tax Benefits Roll Forward [Table Text Block] Surplus notes Surplus Notes Significant Non-Cash Transactions Significant non-cash transactions: Significant Non Cash Transactions Abstract Significant non cash transactions. Second greatest unrealized loss position Second Greatest Unrealized Loss Position Second greatest unrealized loss position. Short-Duration Insurance Contracts, Accident Year 2015 [Member] Short-Duration Insurance Contracts, Accident Year 2015 [Member] Reserve for Losses and Loss Adjustment Expenses Liability for Future Policy Benefits and Unpaid Claims Disclosure [Text Block] Other Comprehensive Income (Loss), Cash Flow Hedge, Gain (Loss), Reclassification, before Tax Other Comprehensive Income (Loss), Cash Flow Hedge, Gain (Loss), Reclassification, before Tax Derivative Contract [Domain] Derivative Contract [Domain] 2030 Defined Benefit Plan, Expected Future Benefit Payment, Year Five Gross realized (losses), available-for-sale fixed maturities Debt Securities, Available-for-Sale, Realized Loss All Individuals All Individuals [Member] Outstanding borrowings capacity including accordion feature Line Of Credit Facility, Maximum Borrowing Capacity, Including Accordion Feature Line Of Credit Facility, Maximum Borrowing Capacity, Including Accordion Feature Long-term Debt, Type [Domain] Long-Term Debt, Type [Domain] Fair Value Disclosures [Abstract] Fair Value Disclosures [Abstract] Name Forgone Recovery, Individual Name Debt Securities, Available-for-sale, Allowance for Credit Loss [Roll Forward] Debt Securities, Available-for-Sale, Allowance for Credit Loss [Roll Forward] Year-over-Year Change in Fair Value of Equity Awards Granted in Prior Years That are Outstanding and Unvested Year-over-Year Change in Fair Value of Equity Awards Granted in Prior Years That are Outstanding and Unvested [Member] Gain on fair value of contingent consideration Business Combination, Contingent Consideration, Change in Contingent Consideration, Asset, Increase (Decrease) Net sales or (purchases) of fixed maturities, trading Proceeds from (Payments for) Trading Securities, Short-Term All other Other Liabilities Not Detailed Other Liabilities Not Detailed Short-term investments Short-term investments Other Short-Term Investments Equity investments Defined Benefit Plan, Equity Securities [Member] Cumulative Number of Reported Claims Short-Duration Insurance Contract, Cumulative Number of Reported Claims Gain on sale of capital assets Gain (Loss) on Sale of Properties Erroneous Compensation Analysis Erroneous Compensation Analysis [Text Block] Other Gain (Loss) on Sale of Other Investments Accumulated other comprehensive income (loss), net of deferred tax expense (benefit) AOCI Tax, Attributable to Parent Lessee, Lease, Description [Line Items] Lessee, Lease, Description [Line Items] Equity in earnings (loss) of unconsolidated subsidiaries Equity in (earnings) loss of unconsolidated subsidiaries Equity in earnings (loss) of unconsolidated subsidiaries Equity In Earnings (Loss) Of Unconsolidated Subsidiaries Equity In Earnings (Loss) Of Unconsolidated Subsidiaries Rule 10b5-1 Arrangement Terminated Rule 10b5-1 Arrangement Terminated [Flag] Tax credit carryforward Deferred Tax Assets, Tax Credit Carryforwards Forecast Forecast [Member] Federal Funds Rate Federal Funds Rate [Member] Federal funds rate. 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Earnings (loss) per share: Earnings Per Share [Abstract] Earnings Per Share [Abstract] Return of invested capital from subsidiaries SEC Schedule, 12-04, Cash Dividends Paid to Registrant, Consolidated Subsidiaries 2030 Lessee, Operating Lease, Liability, to be Paid, Year Five Paid related to: Liability for Unpaid Claims and Claims Adjustment Expense, Claims Paid [Abstract] Return of invested capital from unconsolidated subsidiaries Proceeds from Equity Method Investment, Distribution, Return of Capital Total Policy Liabilities and Accruals Policy Liabilities Total policy liabilities. Other asset-backed securities Other asset-backed securities Asset-Backed Securities, Securitized Loans and Receivables [Member] Tax credit carryforwards Tax Credit Carryforward, Amount Portfolio Cell Reinsurance Portfolio Cell Reinsurance [Member] Portfolio Cell Reinsurance Historical claims duration, year 9 (percent) Short-Duration Insurance Contracts, Historical Claims Duration, Year Nine Net actuarial (gain) loss Other Comprehensive Income (Loss), Defined Benefit Plan, Gain (Loss) Arising During Period, before Tax Number of award types (in award types) Share-based Compensation Arrangement by Share-based Payment Award, Number of Award Types Share-based Compensation Arrangement by Share-based Payment Award, Number of Award Types Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items] Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items] Award Timing Disclosures [Line Items] Schedule of Net Realized Investment Gains (Losses) Gain (Loss) on Securities [Table Text Block] Measurement Frequency [Domain] Measurement Frequency [Domain] Net balance, beginning of year Net balance, end of year Liability for Unpaid Claims and Claims Adjustment Expense, Net Renewal term (in years) Lessee, Operating Lease, Renewal Term Unfunded Contractual Commitments Fair Value, Investments, Entities that Calculate Net Asset Value Per Share, Unfunded Commitments Shareholders' Equity Equity [Text Block] State Deferred State and Local Income Tax Expense (Benefit) Reinsurance Reinsurance [Text Block] Net income (loss) Net income (loss) Net income (loss) Net Income (Loss) Attributable to Parent Interest rate swaps Interest Rate Cash Flow Hedge Liability at Fair Value Schedule of Reconciliation of Expected Income Tax Expense to Actual Income Tax Expense Schedule of Effective Income Tax Rate Reconciliation [Table Text Block] Expected average period (in years) Share-Based Compensation Arrangement by Share-Based Payment Award, Award Vesting Period Allowance for credit loss beginning balance Allowance for credit loss ending balance Credit Losses Recognized In Earnings In Which A Portion Of Losses Are Recognized In Comprehensive Income (Loss), Credit Losses On Debt Securities Held Credit Losses Recognized In Earnings In Which A Portion Of Losses Are Recognized In Comprehensive Income (Loss), Credit Losses On Debt Securities Held Other adjustments Effective Income Tax Rate Reconciliation, Other Adjustments, Percent Segment Reporting Information [Line Items] Segment Reporting Information [Line Items] Authorized preferred stock (in shares) Preferred Stock, Shares Authorized Repurchase of common stock Payments for Repurchase of Common Stock Adoption Date Trading Arrangement Adoption Date Reclassifications Reclassification, Comparability Adjustment [Policy Text Block] Contribution Certificates Contribution Certificate due 2031 [Member] Contribution Certificate due 2031 Tax Year 2039 Tax Year 2039 [Member] Tax Year 2039 Tax Credit Carryforward [Table] Tax Credit Carryforward [Table] Line of Credit Line of Credit [Member] Florida FLORIDA Retained earnings Retained Earnings (Accumulated Deficit) Schedule of Compensation Expense and Related Tax Benefit Recognized During Each Period, and Compensation Cost Expense in Future Periods Share-Based Payment Arrangement, Cost by Plan [Table Text Block] Audit Information [Abstract] Audit Information Alternative market business Alternative Market Business [Member] Alternative Market Business [Member] Year-end Fair Value of Equity Awards Granted in Covered Year that are Outstanding and Unvested Year-end Fair Value of Equity Awards Granted in Covered Year that are Outstanding and Unvested [Member] Initial loss ratio Loss Ratio Net unfavorable prior year reserve development Net Unfavorable Prior Year Reserve Development Net Unfavorable Prior Year Reserve Development (Increase) decrease in cash surrender value of BOLI Life Insurance, Corporate or Bank Owned, Change in Value Cash Flow Hedging Gains (Losses) Accumulated Gain (Loss), Net, Cash Flow Hedge, Parent [Member] Workers' Compensation Insurance Accident and Health Insurance Product Line [Member] Aggregate Grant Date Fair Value of Equity Award Amounts Reported in Summary Compensation Table Aggregate Grant Date Fair Value of Equity Award Amounts Reported in Summary Compensation Table [Member] Other Deferred Tax Liabilities, Other Statement [Table] Statement [Table] Actual return on plan assets Defined Benefit Plan, Plan Assets, Increase (Decrease) for Actual Return (Loss) Securities for which there is an intent to sell or will more likely than not be sold before recovery of amortized cost Debt Securities, Available-for-Sale, Allowance for Credit Loss, Sell before Recovery 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. Adjustments to reconcile net income (loss) to net cash provided (used) by operating activities: Adjustment to Reconcile Net Income to Cash Provided by (Used in) Operating Activity [Abstract] Deferred expense (benefit) Deferred income tax expense (benefit) Total deferred expense (benefit) Deferred Income Tax Expense (Benefit) Short-duration Insurance Contracts, Accident Year [Axis] Short-Duration Insurance Contracts, Accident Year [Axis] Financing Activities Cash Provided by (Used in) Financing Activity, Including Discontinued Operation [Abstract] SEC Schedule, 12-16, Insurance Companies, Supplementary Insurance Information [Line Items] SEC Schedule, 12-16, Insurance Companies, Supplementary Insurance Information [Line Items] Non Government-Backed Non Government-Backed [Member] Securities that are not backed by the U.S. government or U.S. government agencies. All other corporate bonds Other Corporate Bonds [Member] Granted in Year 2019 Granted in Year Two Thousand and Nineteen [Member] Granted in Year Two Thousand and Nineteen Variable Rate [Domain] Variable Rate [Domain] Schedule of Fair Value Measurements - Level 3 Assets & Liabilities Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Table Text Block] All Adjustments to Compensation All Adjustments to Compensation [Member] Recoveries of amounts previously written off Premium Receivable, Allowance for Credit Loss, Recovery Amendment Flag Amendment Flag Tax benefit recognized Share-Based Payment Arrangement, Expense, Tax Benefit Sales Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Liability, Sales Schedule of Allocation of Plan Assets Schedule of Allocation of Plan Assets [Table Text Block] Reserve for losses and loss adjustment expenses Balance, beginning of year Balance, end of year Gross liability for losses and loss adjustment expenses Liability for Claims and Claims Adjustment Expense Condensed Income Statements, Captions [Line Items] Condensed Income Statements, Captions [Line Items] Net investment (gains) losses Gain (Loss) On Sale Of Investments, Excluding Sale Of Properties Gain (Loss) On Sale Of Investments, Excluding Sale Of Properties Treasury shares, at cost (12,606,968 shares as of each respective period end) Treasury Stock, Common, Value Termination Date Trading Arrangement Termination Date Insider Trading Policies and Procedures Adopted Insider Trading Policies and Procedures Adopted [Flag] Number of instruments (in derivative instruments) Number of Instruments Number of Interest Rate Derivatives Held Foreign currency exchange rate (gains) losses Realized Gain (Loss), Foreign Currency Transaction, before Tax SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Table] SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Table] Tranche Three Share-Based Payment Arrangement, Tranche Three [Member] Weighted-average discount rate (as percent) Operating Lease, Weighted Average Discount Rate, Percent Basic (in shares) Weighted average number of common shares outstanding, basic (in shares) Weighted Average Number of Shares Outstanding, Basic Other asset-backed securities Other Asset-Backed Securities [Member] Other Asset-Backed Securities [Member] Schedule of Earnings Per Share, Basic and Diluted Schedule of Earnings Per Share, Basic and Diluted [Table Text Block] Short-duration Insurance Contracts, Historical Claims Duration [Table] Short-Duration Insurance Contracts, Historical Claims Duration [Table] Segment Reporting [Abstract] Segment Reporting [Abstract] Minimum period for claims resolution (in years) Minimum Period For Claims Resolution Minimum Period For Claims Resolution Debt Disclosure [Abstract] Debt Disclosure [Abstract] Defined Benefit Plan, Plan Assets, Category [Axis] Defined Benefit Plan, Plan Assets, Category [Axis] Scenario [Domain] Scenario [Domain] Maximum allowable consolidated funded indebtedness ratio (as percent) Debt Instrument, Restrictive Covenants, Maximum Allowable Consolidated Funded Indebtedness Ratio Debt Instrument, Restrictive Covenants, Maximum Allowable Consolidated Funded Indebtedness Ratio (Ratio is calculated as total debt, including contingent obligations, divided by total non-trade liabilities, plus consolidated shareholders' equity, exclusive of AOCI). SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items] SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items] Borrowings (repayments) under Revolving Credit Agreement Proceeds from (Repayments of) Lines of Credit Cash dividends Dividends, Cash Strategy focused funds Strategy Focused Fund [Member] Strategy Focused Fund [Member] Forgone Recovery due to Expense of Enforcement, Amount Forgone Recovery due to Expense of Enforcement, Amount Share-based Compensation Arrangement by Share-based Payment Award [Line Items] Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items] Consolidated Entities [Axis] Consolidated Entities [Axis] Common shares, par value (in dollars per share) Common stock, par or stated value per share (in dollars per share) Common Stock, Par or Stated Value Per Share Derivative Instruments and Hedging Activities Disclosures [Line Items] Derivative Instruments and Hedging Activities Disclosures [Line Items] Thereafter Defined Benefit Plan, Expected Future Benefit Payment, after Year Five for Next Five Years Reinsurance recoveries Policyholder Benefits and Claims Incurred, Assumed and Ceded Net realized gains (losses), equity investments Equity Securities, FV-NI, Realized Gain (Loss) Effect of cross-border tax laws Effective Income Tax Rate Reconciliation, Cross-Border Tax Effect, Amount Accounting Policies Use of Estimates, Policy [Policy Text Block] Number of insurance subsidiaries Number of Insurance Subsidiaries Number of Insurance Subsidiaries Deferred tax expense (benefit) included in OCI Other Comprehensive Income (Loss), Tax, Portion Attributable to Parent Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Table] Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Table] Reserve for losses and loss adjustment expenses SEC Schedule, 12-16, Insurance Companies, Supplementary Insurance Information, Liability for Future Policy Benefit, Loss, Claim and Loss Expense Insider Trading Arrangements [Line Items] Equity investments Equity Investments Equities Equity Securities [Member] Total Liabilities Liabilities Liabilities 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 Number of major reinsurers Number of Major Reinsurers Number of reinsurers with a balance greater than the major reinsurer individual balance amount threshold Alternative market solutions percentage ceded Alternative Market Solutions Percentage Ceded Alternative Market Solutions Percentage Ceded Pension Adjustments Prior Service Cost Pension Adjustments Prior Service Cost [Member] Fixed maturities, available-for-sale Fixed maturities, available for sale Proceeds from Sale and Maturity of Debt Securities, Available-for-Sale Material Terms of Trading Arrangement Material Terms of Trading Arrangement [Text Block] Segregated Portfolio Cell Reinsurance Segregated Portfolio Cell Reinsurance Segment Segregated Portfolio Cell Reinsurance [Member] Segregated Portfolio Cell Reinsurance [Member] Summary of reserve for losses and loss adjustment expenses Liability for Unpaid Claims and Claims Adjustment Expense [Roll Forward] Operating lease liabilities Deferred Tax Assets, Operating Lease Liability Deferred Tax Assets, Operating Lease Liability Asset-backed Securities Asset-backed securities Asset-Backed Securities [Member] Variable Rate [Axis] Variable Rate [Axis] Less unamortized debt issuance costs Unamortized Debt Issuance Expense Consolidation Items [Axis] Consolidation Items [Axis] Specialty P&C Specialty P&C Segment Specialty Property and Casualty [Member] Specialty Property and Casualty [Member] Deferred tax liabilities Components of Deferred Tax Liabilities [Abstract] Fixed maturities, available-for-sale, at fair value (amortized cost, $3,793,777 and $3,803,835, respectively; allowance for expected credit losses, $4,306 and $3,399, respectively) Fixed maturities available for sale, at fair value Estimated Fair Value Total Fair Value Debt Securities, Available-for-Sale Entity Incorporation, State or Country Code Entity Incorporation, State or Country Code Non-NEOs Non-NEOs [Member] Amount recognized in Consolidated Balance Sheets at December 31 Defined Benefit Plan, Amounts for Asset (Liability) Recognized in Statement of Financial Position Corporate debt Corporate Debt Corporate Debt Securities [Member] Gross premiums earned Gross Premiums Earned Amount of premiums earned before premiums ceded to other entities, including directed and assumed premiums earned.