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Net cash provided by (used in) operating activities Cash Provided by (Used in) Operating Activity, Including Discontinued Operation Investment ownership percentage Investment In Unconsolidated Subsidiaries, Ownership Percentage Investment In Unconsolidated Subsidiaries, Ownership Percentage (Favorable) unfavorable development of reserves established in prior years, net Prior Year Claims and Claims Adjustment Expense Shareholders' Equity Equity, Attributable to Parent [Abstract] Document Transition Report Document Transition Report Fair Value Hierarchy and NAV [Axis] Fair Value Hierarchy and NAV [Axis] Total net investment gains (losses) Gain (Loss) on Investments Liability for Claims and Claims Adjustment Expense [Table] Liability for Claims and Claims Adjustment Expense [Table] Investment, Name [Axis] Investment, Name [Axis] Contribution Certificates Long-term Debt and Contribution Certificates, Fair Value Disclosure Long-term Debt and Contribution Certificates, Fair Value Disclosure Expenses Operating Expenses [Abstract] Deferred tax asset, net Deferred Income Tax Assets, Net Inter-segment Eliminations Intersegment Eliminations [Member] Stock Appreciation Rights (SARs) Stock Appreciation Rights (SARs) [Member] Investment in unconsolidated subsidiaries Investment in unconsolidated subsidiaries Investment In Unconsolidated Subsidiaries Investment In Unconsolidated Subsidiaries Basis spread on variable rate for debt (as percent) Debt Instrument, Basis Spread on Variable Rate Other Commitments [Domain] Other Commitments [Domain] City Area Code City Area Code Total gains (losses) realized and unrealized: Gains Losses Realized and Unrealized Assets [Abstract] Total gains (losses) realized and unrealized. Accumulated Other Comprehensive Income (Loss) Accumulated Other Comprehensive Income (Loss) AOCI Attributable to Parent [Member] All Individuals All Individuals [Member] Corporate Corporate Segment [Member] Revolving Credit Agreement and Term Loan Debt Instrument, Fair Value Disclosure Name Forgone Recovery, Individual Name Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation: Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward] Portion of impairment losses recognized in other comprehensive income (loss) before taxes Portion of impairment losses recognized in other comprehensive income before taxes: Impairment Losses, Investments, Portion In Other Comprehensive Loss, Before Tax, Portion Attributable To Parent Impairment Losses, Investments, Portion In Other Comprehensive Loss, Before Tax, Portion Attributable To Parent Non-GAAP Measure Description Non-GAAP Measure Description [Text Block] Number of investment in any entity or affiliates greater than 10% of stockholders' equity Number of Investment Affiliates Exceeding Shareholder's Equity Ten Percent Threshold Limit Number of Investment Affiliates Exceeding Shareholder's Equity Ten Percent Threshold Limit Statement [Line Items] Statement [Line Items] Total Assets VIEs carrying value Assets Entity [Domain] Entity [Domain] Non-public equity funds Private Equity Funds [Member] Fair Value, Asset, Recurring Basis, Unobservable Input Reconciliation, Asset, Gain (Loss), Statement of Other Comprehensive Income or Comprehensive Income [Extensible Enumeration] Fair Value, Asset, Recurring Basis, Unobservable Input Reconciliation, Asset, Gain (Loss), Statement of Other Comprehensive Income or Comprehensive Income [Extensible Enumeration] Interest expense Interest expense Interest Expense, Operating Net realized gains (losses), equity investments Equity Securities, FV-NI, Realized Gain (Loss) Variable Interest Entity, Not Primary Beneficiary Variable Interest Entity, Not Primary Beneficiary [Member] Net investment income (loss) Interest and Dividend Income, Operating Included in earnings, as a part of: Gains Losses By Earnings Category Assets [Abstract] Included in Earnings, as a part of. Operating segments Operating Segments [Member] Accordion feature borrowing capacity Line of Credit Facility, Maximum Borrowing Capacity, Accordion Feature Line of Credit Facility, Maximum Borrowing Capacity, Accordion Feature Fair value, net asset (liability) Fair Value, Net Asset (Liability) Gross Unrealized Gains Debt Securities, Available-for-Sale, Accumulated Gross Unrealized Gain, before Tax Net sales or maturities (purchases) of short-term investments Payments for (Proceeds from) Short-Term Investments Number of limited partners to allow redemption by special consent Number of Limited Partners to Allow Redemption by Special Consent Number of Limited Partners to Allow Redemption by Special Consent Impairment gains (losses) Total impairment gains (losses): Impairment Losses, Investments Impairment Losses, Investments OCI, before reclassifications, net of tax OCI, before Reclassifications, Net of Tax, Attributable to Parent Other assets Increase (Decrease) in Other Operating Assets PEO PEO [Member] Corporate debt, limited observable inputs Corporate debt, limited observable inputs Corporate Debt, Limited Observable Inputs [Member] Corporate Debt, Limited Observable Inputs [Member] Lloyd's Syndicates Lloyd's Syndicates [Member] Lloyd's Syndicates [Member] Measurement Basis [Axis] Measurement Basis [Axis] Goodwill Goodwill Forgone Recovery due to Violation of Home Country Law, Amount Forgone Recovery due to Violation of Home Country Law, Amount BOLI Investment Income (Loss), Bank Owned Life Insurance Investment Income (Loss), Bank Owned Life Insurance Debt securities in unrealized loss position (in securities) Debt Securities, Available-for-Sale, Unrealized Loss Position, Number of Positions Product Information [Line Items] Product Information [Line Items] Fair Value Measurement Inputs and Valuation Techniques [Line Items] Fair Value Measurement Inputs and Valuation Techniques [Line Items] Total Investments Investments 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 Retained Earnings Retained Earnings [Member] Revolving Credit Facility Revolving Credit Facility [Member] Erroneously Awarded Compensation Recovery Erroneously Awarded Compensation Recovery [Table] Required FAL deposit Deposit Assets Schedule of Quantitative Information Regarding Level 3 Valuations Fair Value Measurement Inputs and Valuation Techniques [Table Text Block] Increase (Decrease) in Stockholders' Equity: Increase (Decrease) in Stockholders' Equity [Roll Forward] Award Timing Disclosures [Line Items] Schedule of Financial Instruments Not Measured at Fair Value Fair Value, by Balance Sheet Grouping [Table Text Block] Corporate Debt Corporate debt Corporate Debt Securities [Member] Diluted (in usd per share) Earnings Per Share, Diluted Entity Current Reporting Status Entity Current Reporting Status Net cash provided by (used in) financing activities Cash Provided by (Used in) Financing Activity, Including Discontinued Operation Threshold limit of investments based on shareholders' equity Threshold Limit Of Investments Based On Shareholders Equity Threshold Limit Of Investments Based On Shareholders Equity Total Shareholder Return Amount Total Shareholder Return Amount Net favorable prior year reserve development Net Favorable Prior Year Reserve Development Net Favorable Prior Year Reserve Development Liabilities: Liabilities, Fair Value Disclosure [Abstract] 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] Financing Activities Cash Provided by (Used in) Financing Activity, Including Discontinued Operation [Abstract] Real estate, net Property, Plant, and Equipment, after Accumulated Depreciation, Depletion, and Amortization Other net investment gains (losses) Other Net Realized Investment Gain (Loss) Other net realized investment gains (losses). Financial Instruments [Domain] Financial Instruments [Domain] All other All Other [Member] All Other Qualified affordable housing project tax credit partnerships Qualified Affordable Housing Tax Credit Partnerships [Member] Qualified Affordable Housing Tax Credit Partnerships [Member] Prepaid reinsurance premiums Prepaid Reinsurance Premiums Schedule of Equity Method Investments Equity Method Investments [Table Text Block] Financial assets: Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract] Estimated Fair Value Derivative Asset Other income (expense) Other income (expense) Other income (expense) Other Income Equity Awards Adjustments, Footnote Equity Awards Adjustments, Footnote [Text Block] Investment redemption notice period 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 Underlying Securities Award Underlying Securities Amount Fair Value Estimate of Fair Value Measurement [Member] Private debt funds Private Debt Funds [Member] Private Debt Funds [Member] Sales Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Sales Other Payment for (Proceeds from) Other Investing Activity Change in unrealized holding gains (losses), trading fixed maturities Debt Securities, Trading, Unrealized Gain (Loss) Proceeds from sales or maturities of: Proceeds from Sale, Maturity and Collection of Investments [Abstract] Number of limited partners in investment Number of Limited Partners In Investment Number of Limited Partners In Investment Segment Reporting [Table] Segment Reporting [Table] Provision for income taxes: Income Tax Expense (Benefit), Continuing Operations [Abstract] Schedule of Equity Method Investments [Table] Equity Method Investment [Table] Schedule of Available-For-Sale Fixed Maturities Schedule of Available-for-Sale Securities Reconciliation [Table Text Block] Commitments and Contingencies Disclosure [Abstract] Commitments and Contingencies Disclosure [Abstract] All Trading Arrangements All Trading Arrangements [Member] Less than 12 months, Fair Value Debt Securities, Available-for-Sale, Continuous Unrealized Loss Position, Less than 12 Months Other Performance Measure, Amount Other Performance Measure, Amount Award Timing MNPI Considered Award Timing MNPI Considered [Flag] Other investments, portion carried at fair value Other Investments, Fair Value Disclosure Other Investments, Fair Value Disclosure Current Fiscal Year End Date Current Fiscal Year End Date BOLI BOLI Cash Surrender Value [Member] Non-PEO NEO Average Total Compensation Amount Non-PEO NEO Average Total Compensation Amount Derivative [Line Items] Derivative [Line Items] Pre-tax transaction related costs Business Combination, Acquisition Related Costs, Before Tax Business Combination, Acquisition Related Costs, Before Tax Foreign currency exchange rate gains (losses) Unrealized Gain (Loss), Foreign Currency Transaction, after Tax Fair value Investments continuous unrealized loss position [Abstract] Investments Continuous Unrealized Loss Position. Change in Fair Value as of Vesting Date of Prior Year Equity Awards Vested in Covered Year Change in Fair Value as of Vesting Date of Prior Year Equity Awards Vested in Covered Year [Member] Entity File Number Entity File Number Rule 10b5-1 Arrangement Adopted Rule 10b5-1 Arrangement Adopted [Flag] Due in one year or less Debt Securities, Available-for-Sale, Maturity, Allocated and Single Maturity Date, Rolling within One Year, Fair Value Net effect of restricted and performance shares issued Shares Issued, Value, Share-Based Payment Arrangement, after Forfeiture Schedule of Available-For-Sale Securities by Contractual Maturity Investments Classified by Contractual Maturity Date [Table Text Block] Equity investments Equities Equity Securities [Member] Schedule of Reserve for Losses and Loss Adjustment Expenses Schedule of Liability for Unpaid Claims and Claims Adjustment Expense [Table Text Block] Assets measured at fair value Debt Securities, Available-for-Sale, Measurement Input Recovery of Erroneously Awarded Compensation Disclosure [Line Items] Common shares, shares issued (in shares) Common Stock, Shares, Issued Measure: Measure [Axis] Beginning balance Ending balance Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Value Treasury shares (in shares) Treasury Stock, Common, Shares Net premiums earned Net premiums earned Segment net premiums earned Premiums Earned, Net Workers' Compensation Insurance Workers' Compensation Insurance Segment Workers' Compensation Insurance Segment [Member] Workers' Compensation Insurance Segment Allowance for expected credit losses Allowance for Expected Credit Losses Allowance for credit loss beginning balance Allowance for credit loss ending balance Debt Securities, Available-for-Sale, Allowance for Credit Loss Deferred tax expense (benefit) on accumulated other comprehensive income (loss) AOCI Tax, Attributable to Parent 12 months or longer, Unrealized Loss Debt Securities, Available-for-Sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss Equity Components [Axis] Equity Components [Axis] Equity Components [Axis] Product and Service [Domain] Product and Service [Domain] SPC U.S. federal income tax expense (benefit) SPC U.S. federal income tax benefit (expense) Segregated Portfolio Cells Income Tax Expense (Benefit) Segregated Portfolio Cells Income Tax Expense (Benefit) Short-term investments, including Other Short-Term Investments and Other Invested Assets [Member] Short-term investments and Other invested assets [Member] Schedule of Credit Derivatives [Table] Credit Derivative [Table] Entity Interactive Data Current Entity Interactive Data Current Deferred compensation liabilities Deferred Compensation Liability, Current and Noncurrent Variable Interest Entity [Line Items] Variable Interest Entity [Line Items] Compensation Actually Paid vs. Other Measure Compensation Actually Paid vs. Other Measure [Text Block] Foreign Currency Forwards Derivative Instruments Not Designated as Hedging Instruments, Gain (Loss), Net Fixed maturities, available-for-sale Debt Securities, Available-for-Sale, Maturity, Allocated and Single Maturity Date, Fair Value [Abstract] Entity Small Business Entity Small Business Accumulated Other Comprehensive Income (Loss) [Line Items] Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items] Comprehensive income (loss) Comprehensive Income (Loss), Net of Tax, Attributable to Parent Unearned premiums Unearned Premiums Termination Date Trading Arrangement Termination Date Other Commitments [Axis] Other Commitments [Axis] 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. Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Table] Fair Value, Recurring and Nonrecurring [Table] Accident Year [Axis] Accident Year [Axis] Accident Year Schedule of Investments in LLCs and Limited Partnerships Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Table Text Block] Unsettled security transactions, net change Unsettled security transactions net Unsettled security transactions, net. Compensation Actually Paid vs. Total Shareholder Return Compensation Actually Paid vs. Total Shareholder Return [Text Block] MNPI Disclosure Timed for Compensation Value MNPI Disclosure Timed for Compensation Value [Flag] Current year Current Year Claims and Claims Adjustment Expense U.S. Government-sponsored enterprise obligations U.S. Government-sponsored enterprise obligations US Government-sponsored Enterprises Debt Securities [Member] Document Type Document Type Second greatest unrealized loss position Second Greatest Unrealized Loss Position Second greatest unrealized loss position. Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] Fair Value as of Grant Date Award Grant Date Fair Value Tax credit carryforwards Tax Credit Carryforward, Amount Schedule of Investments Held in an Unrealized Loss Position Debt Securities, Available-for-Sale, Unrealized Loss Position, Fair Value [Table Text Block] Pay vs Performance Disclosure, Table Pay vs Performance [Table Text Block] Line of credit, borrowing capacity including accordion feature Line Of Credit Facility, Maximum Borrowing Capacity, Including Accordion Feature Line Of Credit Facility, Maximum Borrowing Capacity, Including Accordion Feature Arrangement Duration Trading Arrangement Duration Statement of Stockholders' Equity [Abstract] Statement of Stockholders' Equity [Abstract] Local Phone Number Local Phone Number Consolidation Items [Axis] Consolidation Items [Axis] Entity Address, Postal Zip Code Entity Address, Postal Zip Code Entity Registrant Name Entity Registrant Name Purchases of capital assets Payments to Acquire Other Productive Assets Short-term investments Other Short-Term Investments Less than 12 months, Unrealized Loss Debt Securities, Available-for-Sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss Pledged Status [Domain] Pledged Status [Domain] Income (loss) before income taxes Income (Loss) from Continuing Operations before Income Taxes, Noncontrolling Interest Insider Trading Policies and Procedures Not Adopted Insider Trading Policies and Procedures Not Adopted [Text Block] Total revenues Revenues Changed Peer Group, Footnote Changed Peer Group, Footnote [Text Block] Fair Value Alternative Investment Forgone Recovery due to Expense of Enforcement, Amount Forgone Recovery due to Expense of Enforcement, Amount Executive Category: Executive Category [Axis] No allowance for credit losses has been previously recognized Debt Securities, Available-for-Sale, Allowance for Credit Loss, Not Previously Recorded Unrealized Investment Gains (Losses) AOCI, Gain (Loss), Debt Securities, Available-for-Sale, without Allowance for Credit Loss, Parent [Member] Liabilities and Shareholders' Equity Liabilities and Equity [Abstract] Other Commitments [Table] Other Commitments [Table] Schedule of Fair Value of Assets Schedule of Fair Value, Assets and Liabilities Measured on Recurring Basis [Table Text Block] 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 Award Type [Domain] Award Type [Domain] NORCAL Group NORCAL Group [Member] NORCAL Group [Member] Non-PEO NEO Average Compensation Actually Paid Amount Non-PEO NEO Average Compensation Actually Paid Amount Fair Value Measurement Fair Value Disclosures [Text Block] Variable Interest Entities [Table] Variable Interest Entity [Table] Level 3 Fair Value, Inputs, Level 3 [Member] Cash Flow Hedge- Interest Rate Swaps Other Comprehensive Income (Loss), Cash Flow Hedge, Gain (Loss), Reclassification, after Tax Asset Pledged as Collateral Asset Pledged as Collateral [Member] PEO Name PEO Name Total paid Liability for Unpaid Claims and Claims Adjustment Expense, Claims Paid Cash Flow Hedging Gains (Losses) Accumulated Gain (Loss), Net, Cash Flow Hedge, Parent [Member] Debt Securities, Available-for-sale, Allowance for Credit Loss [Line Items] Debt Securities, Available-for-Sale, Allowance for Credit Loss [Line Items] Fair Value Measured at Net Asset Value Per Share Fair Value Measured at Net Asset Value Per Share [Member] Financial liabilities: Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract] Other assets Other Assets Stock Price or TSR Estimation Method Stock Price or TSR Estimation Method [Text Block] Single greatest unrealized loss position Single Greatest Unrealized Loss Position Single greatest unrealized loss position. Entity Tax Identification Number Entity Tax Identification Number Legal Entity [Axis] Legal Entity [Axis] Other Commitments [Line Items] Other Commitments [Line Items] 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. Total Policy Liabilities and Accruals Policy Liabilities Total policy liabilities. Cash and cash equivalents at beginning of period Cash and cash equivalents at end of period Cash, Cash Equivalent, Restricted Cash, and Restricted Cash Equivalent, Continuing Operation Entity Incorporation, State or Country Code Entity Incorporation, State or Country Code Aggregate Erroneous Compensation Not Yet Determined Aggregate Erroneous Compensation Not Yet Determined [Text Block] Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Table] Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Table] Material Terms of Trading Arrangement Material Terms of Trading Arrangement [Text Block] Non-NEOs Non-NEOs [Member] Vesting Date Fair Value of Equity Awards Granted and Vested in Covered Year Vesting Date Fair Value of Equity Awards Granted and Vested in Covered Year [Member] Basis of Presentation Organization, Consolidation and Presentation of Financial Statements Disclosure [Text Block] Debt Instrument [Axis] Debt Instrument [Axis] Measurement Frequency [Domain] Measurement Frequency [Domain] Share-based compensation Share-Based Payment Arrangement, Noncash Expense Tax Period [Axis] Tax Period [Axis] Investment, Name [Domain] Investment, Name [Domain] Long-term Debt, Type [Domain] Long-Term Debt, Type [Domain] Basic (in usd per share) Earnings Per Share, Basic Measurement Input Type [Axis] Measurement Input Type [Axis] Other asset-backed securities Collateralized Mortgage-Backed Securities [Member] Statistical Measurement [Axis] Statistical Measurement [Axis] Insider Trading Arrangements [Line Items] Losses (gains) recorded Investment Program, Proportional Amortization Method, Elected, Equity Method Investment, Income (Loss) from Tax Credit Investment Schedule of Derivative Instruments, Gain (Loss) Derivative Instruments, Gain (Loss) [Table Text Block] Comparability Adjustment Measurement Input, Comparability Adjustment [Member] Award Type [Axis] Award Type [Axis] Named Executive Officers, Footnote Named Executive Officers, Footnote [Text Block] Retained earnings Retained Earnings (Accumulated Deficit) Product and Service [Axis] Product and Service [Axis] DPAC amortization Deferred Policy Acquisition Costs, Amortization Expense Net cash impact of deconsolidation of closed years of account from Lloyd's Syndicates operations Closed Block Operations, Net Results Aggregate Change in Present Value of Accumulated Benefit for All Pension Plans Reported in Summary Compensation Table Aggregate Change in Present Value of Accumulated Benefit for All Pension Plans Reported in Summary Compensation Table [Member] Awards Close in Time to MNPI Disclosures Awards Close in Time to MNPI Disclosures [Table] 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. Common Stock Common Stock [Member] Fixed maturities, available-for-sale, at fair value (amortized cost, $3,775,708 and $3,793,777, respectively; allowance for expected credit losses, $4,299 and $4,306, respectively) Fixed maturities, available-for-sale Estimated Fair Value Total Fair Value Debt Securities, Available-for-Sale Fair Value Measurement [Domain] Fair Value Measurement [Domain] Reclassification out of Accumulated Other Comprehensive Income [Table] Reclassification out of Accumulated Other Comprehensive Income [Table] 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 Compensation Actually Paid vs. Company Selected Measure Compensation Actually Paid vs. Company Selected Measure [Text Block] Cover [Abstract] Cover [Abstract] Insurance [Abstract] Insurance [Abstract] Proceeds from sale of capital assets Proceeds from Sale of Other Productive Assets Contribution Certificates Contribution Certificate due 2031 [Member] Contribution Certificate due 2031 Tax Year 2039 Tax Year 2039 [Member] Tax Year 2039 Fair Value Measurement Inputs and Valuation Techniques [Table] Fair Value Measurement Inputs and Valuation Techniques [Table] All other Other Income, Other Other Income, Other Derivative Contract [Domain] Derivative Contract [Domain] Funding Commitments Funding Commitments [Member] Funding Commitments [Member] Equity Awards Adjustments Equity Awards Adjustments [Member] Total Liabilities and Shareholders' Equity Liabilities and Equity Employee Stock Option Share-Based Payment Arrangement, Option [Member] Purchases Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Purchases Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] Alternative market business Alternative Market Business [Member] Alternative Market Business [Member] Segments [Axis] Segments [Axis] Other liabilities Increase (Decrease) in Other Operating Liabilities Business owned life insurance Life Insurance, Corporate or Bank Owned, Amount Additional 402(v) Disclosure Additional 402(v) Disclosure [Text Block] Fixed maturities, trading, at fair value (cost, $13,487 and $14,202, respectively) Fixed maturities, trading Debt Securities, Trading Premiums receivable Increase (Decrease) in Premiums Receivable Tabular List, Table Tabular List [Table Text Block] Non-credit Impairments AOCI, Gain (Loss), Debt Securities, Available-for-Sale, with Allowance for Credit Loss, Parent [Member] Receivable from reinsurers on unpaid losses and loss adjustment expenses Less reinsurance recoverables on unpaid losses and loss adjustment expenses Plus reinsurance recoverables on unpaid losses and loss adjustment expenses Reinsurance Recoverable for Unpaid Claims and Claims Adjustments Reserve for Losses and Loss Adjustment Expenses Liability for Future Policy Benefits and Unpaid Claims Disclosure [Text Block] Debt Long-Term Debt [Text Block] Deferred policy acquisition costs and amortization Deferred Policy Acquisition Costs, Amortization Expense, Excluding Accrued Interest Short-term investments Short-Term Investments [Member] Name Awards Close in Time to MNPI Disclosures, Individual Name Change in unrealized holding gains (losses), convertible securities, carried at fair value Unrealized Gain (Loss) on Hybrid Instrument, Net 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] Market Comparable Securities Valuation, Market Approach [Member] 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. 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 Preferred stock, shares authorized (in shares) Preferred Stock, Shares Authorized Non government-backed Non Government-Backed [Member] Securities that are not backed by the U.S. government or U.S. government agencies. Adjustment to Compensation: Adjustment to Compensation [Axis] Other commercial mortgage-backed securities Other commercial mortgage-backed securities Commercial Mortgage-Backed Securities [Member] Rule 10b5-1 Arrangement Terminated Rule 10b5-1 Arrangement Terminated [Flag] Aggregate Erroneous Compensation Amount Aggregate Erroneous Compensation Amount Statement of Cash Flows [Abstract] Statement of Cash Flows [Abstract] Net sales or (purchases) of fixed maturities, trading Proceeds from (Payments for) Trading Securities, Short-Term Interest rate swaps Interest Rate Cash Flow Hedge Liability at Fair Value Net investment (gains) losses Net investment gains (losses) Gain (Loss) on Sale of Investments, Excluding Sale of Properties Gain (Loss) on Sale of Investments, Excluding Sale of Properties Foreign Currency Forwards Foreign Exchange Forward [Member] Commitments total Other Commitment PPM RRG PPM RRG [Member] PPM RRG Credit Facility [Axis] Credit Facility [Axis] Aggregate Available Trading Arrangement, Securities Aggregate Available Amount Total assets categorized within the fair value hierarchy Assets, Fair Value Disclosure Name Measure Name Summary of reserve for losses and loss adjustment expenses Liability for Unpaid Claims and Claims Adjustment Expense [Roll Forward] Income Taxes Income Tax Disclosure [Text Block] Pay vs Performance Disclosure [Line Items] Fair Value, Measurements, Fair Value Hierarchy [Domain] Fair Value Hierarchy and NAV [Domain] Other, net Other Noncash Income (Expense) Agency commercial mortgage-backed securities Agency commercial mortgage-backed securities Government National Mortgage Association Certificates and Obligations (GNMA) [Member] MPL MPL [Member] MPL Debt Instrument [Line Items] Debt Instrument [Line Items] Other asset-backed securities Other Asset-Backed Securities [Member] Other Asset-Backed Securities [Member] Pay vs Performance Disclosure Pay vs Performance Disclosure [Table] Debt Securities, Available-for-sale, Allowance for Credit Loss [Table] Debt Securities, Available-for-Sale, Allowance for Credit Loss [Table] Reserve for losses and loss adjustment expenses Increase (Decrease) in Liability for Claims and Claims Adjustment Expense Reserve Tax credits recognized Investment Program, Proportional Amortization Method, Elected, Income Tax Credit and Other Income Tax Benefit, before Amortization Expense Additional Paid-in Capital Additional Paid-in Capital [Member] Entity Filer Category Entity Filer Category Fair Value Debt Securities, Available-for-Sale, Unrealized Loss Position Income tax benefit (expense) Income Tax Expense (Benefit), Excluding Business Acquisition Tax Effect Income Tax Expense (Benefit), Excluding Business Acquisition Tax Effect Minimum period for claims resolution (in years) Minimum Period For Claims Resolution Minimum Period For Claims Resolution Name Trading Arrangement, Individual Name Other liabilities Other Liabilities, Fair Value Disclosure Cash and cash equivalents Cash and Cash Equivalent Purchases of: Payments to Acquire Investments [Abstract] Debt Securities, Available-for-sale, Allowance for Credit Loss [Roll Forward] Other than Temporary Impairment, Credit Losses Recognized in Earnings [Roll Forward] Net investment gains (losses): Realized Investment Gains (Losses) [Abstract] Other Other Premiums [Member] Other Premiums [Member] Strategy focused funds Strategy Focused Fund [Member] Strategy Focused Fund [Member] Company Selected Measure Amount Company Selected Measure Amount Tax Period [Domain] Tax Period [Domain] Change in unrealized holding gains (losses), equity investments Equity Securities, FV-NI, Unrealized Gain (Loss) Investments, Debt and Equity Securities [Abstract] Investments, Debt and Equity Securities [Abstract] Schedule of Net Realized Investment Gains (Losses) Gain (Loss) on Securities [Table Text Block] Change in unrealized gains (losses) included in earnings for the above period for Level 3 assets and liabilities held at period-end Fair Value, Asset, Recurring Basis, Still Held, Unrealized Gain (Loss) Fair Value, Asset, Recurring Basis, Unobservable Input Reconciliation, Gain (Loss), Statement of Income or Comprehensive Income [Extensible Enumeration] Fair Value, Asset, Recurring Basis, Unobservable Input Reconciliation, Gain (Loss), Statement of Income or Comprehensive Income [Extensible Enumeration] (Increase) decrease in cash surrender value of BOLI Life Insurance, Corporate or Bank Owned, Change in Value Securities sold during the period Debt Securities, Available-for-Sale, Allowance for Credit Loss, Securities Sold Number of proassurance's insurance subsidiaries Number of Insurance Subsidiaries Number of Insurance Subsidiaries Non-PEO NEO Non-PEO NEO [Member] Entity Address, Address Line One Entity Address, Address Line One Total expenses Benefits, Losses and Expenses Total income tax expense (benefit) Income tax benefit Income Tax Expense (Benefit) Securities on deposit with state insurance departments Assets Held by Insurance Regulators Award Timing Method Award Timing Method [Text Block] Increase (decrease) in cash and cash equivalents Cash, Cash Equivalent, Restricted Cash, and Restricted Cash Equivalent, Period Increase (Decrease), Including Exchange Rate Effect and Discontinued Operation Forecast Forecast [Member] Forgone Recovery, Explanation of Impracticability Forgone Recovery, Explanation of Impracticability [Text Block] Premiums receivable, net (allowance for expected credit losses, $7,951 and $7,829, respectively) Premiums Receivable, Net Intangible assets, net Other Intangible Assets, Net Variable Interest Entity, Primary Beneficiary Variable Interest Entity, Primary Beneficiary [Member] 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 AOCI Attributable to Parent, Net of Tax [Roll Forward] AOCI Attributable to Parent, Net of Tax [Roll Forward] Net income (loss) Net income (loss) Net Income (Loss) Attributable to Parent Long-term Debt, Type [Axis] Long-Term Debt, Type [Axis] Erroneous Compensation Analysis Erroneous Compensation Analysis [Text Block] Less unamortized debt issuance costs Unamortized Debt Issuance Expense Statement [Table] Statement [Table] Segment reconciling items Segment Reporting, Reconciling Item, Excluding Corporate Nonsegment [Member] Restatement Determination Date: Restatement Determination Date [Axis] Schedule of Components of AOCI, Net of Tax Schedule of Accumulated Other Comprehensive Income (Loss) [Table Text Block] Segregated Portfolio Cell Reinsurance Segregated Portfolio Cell Reinsurance Segment Segregated Portfolio Cell Reinsurance [Member] Segregated Portfolio Cell Reinsurance [Member] Net realized gains (losses), trading fixed maturities Debt Securities, Trading, Realized Gain (Loss) Specialty P&C Specialty P&C Specialty P&C Segment Specialty Property and Casualty [Member] Specialty Property and Casualty [Member] Revolving Credit Agreement Revolving Credit Agreement [Member] Revolving Credit Agreement Borrowings (repayments) under Revolving Credit Agreement Proceeds from (Repayments of) Lines of Credit Accident Year 2022 and 2024 Accident Year 2022 and 2024 [Member] Accident Year 2022 and 2024 Revenues Revenues [Abstract] Gross premiums earned: Gross Premiums Earned Amount of premiums earned before premiums ceded to other entities, including directed and assumed premiums earned. Pension Benefits Adjustments, Footnote Pension Benefits Adjustments, Footnote [Text Block] Other investments Other Long-Term Investments [Member] Derivative Instruments and Hedging Activities Disclosure [Abstract] Derivative Instruments and Hedging Activities Disclosure [Abstract]