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Fair Value Measurements - Fair Value Inputs (Details) - USD ($) | 3 Months Ended | 9 Months Ended |  |  |  |
--- | --- | --- | --- | --- | --- | ---
Sep. 30, 2023 | Sep. 30, 2022 | Sep. 30, 2023 | Sep. 30, 2022 | Jun. 30, 2023 | Dec. 31, 2022 | Jun. 30, 2022 | Dec. 31, 2021
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |  |  |  |
Fixed maturities at fair value | $ 6,474,500,000 |  | $ 6,474,500,000 |  |  | $ 6,894,800,000 |  |
Equity securities | 233,400,000 |  | 233,400,000 |  |  | 243,200,000 |  |
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Purchases | 6,200,000 | $ 96,200,000 | 45,200,000 | $ 119,800,000 |  |  |  |
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Transfers Into Level 3 | 5,000,000.0 | 17,600,000 | 5,400,000 | 22,900,000 |  |  |  |
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Value | 197,600,000 | 233,200,000 | 197,600,000 | 233,200,000 | $ 201,500,000 | 230,000,000.0 | $ 191,300,000 | $ 251,400,000
Included in Condensed Consolidated Statement of Operations | 1,700,000 | (6,300,000) | 800,000 | (12,200,000) |  |  |  |
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Transfers out of Level 3 | 0 | 0 | (100,000) | (5,700,000) |  |  |  |
Included in Other Comprehensive Income (Loss) | (2,700,000) | (3,300,000) | (300,000) | (15,100,000) |  |  |  |
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Settlements | 0 | 0 | 0 | 0 |  |  |  |
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Sales | (14,100,000) | (62,300,000) | (83,400,000) | (127,900,000) |  |  |  |
Fair Value, Equity Securities FV-NI, Entities That Calculate Net Asset Value Per Share, Unfunded Commitments | 0 |  | 0 |  |  | 0 |  |
Fair Value, Equity Method Investments, Entities That Calculate Net Asset Value Per Share, Unfunded Commitments | 89,400,000 |  | 89,400,000 |  |  | 95,900,000 |  |
Other Funds |  |  |  |  |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |  |  |  |
Fair Value, Alternative Investments, Entities That Calculate Net Asset Value Per Share, Unfunded Commitments | 0 |  | 0 |  |  | 200,000 |  |
Fair Value, Equity Method Investments, Entities That Calculate Net Asset Value Per Share, Unfunded Commitments | 0 |  | 0 |  |  | 0 |  |
Equity Securities |  |  |  |  |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |  |  |  |
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Purchases | 0 | 2,700,000 | 1,100,000 | 2,700,000 |  |  |  |
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Transfers Into Level 3 | 0 | 0 | 400,000 | 0 |  |  |  |
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Value | 3,700,000 | 2,500,000 | 3,700,000 | 2,500,000 | 2,200,000 | 2,100,000 | 1,700,000 | 1,500,000
Included in Condensed Consolidated Statement of Operations | 1,500,000 | 0 | 100,000 | 0 |  |  |  |
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Transfers out of Level 3 | 0 |  | 0 | 0 |  |  |  |
Included in Other Comprehensive Income (Loss) | 0 | 0 | 0 | 200,000 |  |  |  |
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Settlements | 0 | 0 | 0 | 0 |  |  |  |
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Sales | 0 | (1,900,000) | 0 | (1,900,000) |  |  |  |
States and Political Subdivisions |  |  |  |  |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |  |  |  |
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Purchases | 100,000 |  | 100,000 |  |  |  |  |
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Transfers Into Level 3 | 0 |  | 0 |  |  |  |  |
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Value | 100,000 |  | 100,000 |  |  | 0 |  |
Included in Condensed Consolidated Statement of Operations | 0 |  | 0 |  |  |  |  |
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Transfers out of Level 3 | 0 |  | 0 |  |  |  |  |
Included in Other Comprehensive Income (Loss) | 0 |  | 0 |  |  |  |  |
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Settlements | 0 |  | 0 |  |  |  |  |
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Sales | 0 |  | 0 |  |  |  |  |
Redeemable Preferred Stocks |  |  |  |  |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |  |  |  |
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Purchases | 0 | 0 | 0 | 2,000,000.0 |  |  |  |
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Transfers Into Level 3 |  | 0 | 0 | 0 |  |  |  |
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Value | 6,600,000 | 6,800,000 | 6,600,000 | 6,800,000 | $ 6,700,000 | 6,800,000 | $ 6,900,000 | $ 6,100,000
Included in Condensed Consolidated Statement of Operations | 0 | 0 | 0 | 0 |  |  |  |
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Transfers out of Level 3 |  | 0 | 0 | 0 |  |  |  |
Included in Other Comprehensive Income (Loss) | (100,000) | (100,000) | (200,000) | (1,300,000) |  |  |  |
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Settlements | 0 | 0 | 0 | 0 |  |  |  |
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Sales | 0 | $ 0 | 0 | $ 0 |  |  |  |
Fair Value Measured at Net Asset Value Per Share |  |  |  |  |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |  |  |  |
Total Assets | 440,100,000 |  | 440,100,000 |  |  | 430,700,000 |  |
Fair Value, Alternative Investments, Entities That Calculate Net Asset Value Per Share, Unfunded Commitments | 103,300,000 |  | 103,300,000 |  |  | 96,300,000 |  |
Fair Value, Measurements, Recurring |  |  |  |  |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |  |  |  |
Convertible debt at fair value | 45,900,000 |  | 45,900,000 |  |  | 43,300,000 |  |
Total Assets | 6,753,800,000 |  | 6,753,800,000 |  |  | 7,183,000,000 |  |
Derivative Asset |  |  |  |  |  | 1,700,000 |  |
Liabilities, Fair Value Disclosure | (15,600,000) |  | (15,600,000) |  |  | 400,000 |  |
Fair Value, Measurements, Recurring | Investments in Fixed Maturities |  |  |  |  |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |  |  |  |
Fixed maturities at fair value | 6,474,500,000 |  | 6,474,500,000 |  |  | 6,894,800,000 |  |
Fair Value, Measurements, Recurring | U.S. Government and Government Agencies and Authorities |  |  |  |  |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |  |  |  |
Fixed maturities at fair value | 487,200,000 |  | 487,200,000 |  |  | 528,000,000.0 |  |
Fair Value, Measurements, Recurring | States and Political Subdivisions |  |  |  |  |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |  |  |  |
Fixed maturities at fair value | 1,320,200,000 |  | 1,320,200,000 |  |  | 1,568,900,000 |  |
Fair Value, Measurements, Recurring | Foreign Governments |  |  |  |  |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |  |  |  |
Fixed maturities at fair value | 4,200,000 |  | 4,200,000 |  |  | 4,100,000 |  |
Fair Value, Measurements, Recurring | Bonds and Notes |  |  |  |  |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |  |  |  |
Fixed maturities at fair value | 3,394,400,000 |  | 3,394,400,000 |  |  | 3,539,400,000 |  |
Fair Value, Measurements, Recurring | Redeemable Preferred Stocks |  |  |  |  |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |  |  |  |
Fixed maturities at fair value | 7,800,000 |  | 7,800,000 |  |  | 8,000,000.0 |  |
Fair Value, Measurements, Recurring | Collateralized Loan Obligations |  |  |  |  |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |  |  |  |
Fixed maturities at fair value | 956,200,000 |  | 956,200,000 |  |  | 953,900,000 |  |
Fair Value, Measurements, Recurring | Other Mortgage- and Asset-backed |  |  |  |  |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |  |  |  |
Fixed maturities at fair value | 304,500,000 |  | 304,500,000 |  |  | 292,500,000 |  |
Fair Value, Measurements, Recurring | Equity Securities |  |  |  |  |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |  |  |  |
Equity securities | 233,400,000 |  | 233,400,000 |  |  | 243,200,000 |  |
Fair Value, Measurements, Recurring | Exchange Traded Funds |  |  |  |  |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |  |  |  |
Equity securities | 7,100,000 |  | 7,100,000 |  |  | 12,200,000 |  |
Fair Value, Measurements, Recurring | Limited Liability Companies and Limited Partnerships |  |  |  |  |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |  |  |  |
Equity securities | 193,500,000 |  | 193,500,000 |  |  | 189,100,000 |  |
Fair Value, Measurements, Recurring | Designated as Hedging Instrument |  |  |  |  |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |  |  |  |
Derivative Asset |  |  |  |  |  | (400,000) |  |
Derivative Liability | (15,600,000) |  | (15,600,000) |  |  |  |  |
Fair Value, Measurements, Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1) |  |  |  |  |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |  |  |  |
Convertible debt at fair value | 0 |  | 0 |  |  |  |  |
Total Assets | 102,300,000 |  | 102,300,000 |  |  | 117,000,000.0 |  |
Convertible Securities, Fair Value Disclosures |  |  |  |  |  | 0 |  |
Derivative Asset |  |  |  |  |  | 0 |  |
Liabilities, Fair Value Disclosure | 0 |  | 0 |  |  | 0 |  |
Fair Value, Measurements, Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1) | Investments in Fixed Maturities |  |  |  |  |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |  |  |  |
Fixed maturities at fair value | 94,400,000 |  | 94,400,000 |  |  | 103,600,000 |  |
Fair Value, Measurements, Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1) | U.S. Government and Government Agencies and Authorities |  |  |  |  |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |  |  |  |
Fixed maturities at fair value | 94,400,000 |  | 94,400,000 |  |  | 103,600,000 |  |
Fair Value, Measurements, Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1) | States and Political Subdivisions |  |  |  |  |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |  |  |  |
Fixed maturities at fair value | 0 |  | 0 |  |  | 0 |  |
Fair Value, Measurements, Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1) | Foreign Governments |  |  |  |  |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |  |  |  |
Fixed maturities at fair value | 0 |  | 0 |  |  | 0 |  |
Fair Value, Measurements, Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1) | Bonds and Notes |  |  |  |  |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |  |  |  |
Fixed maturities at fair value | 0 |  | 0 |  |  | 0 |  |
Fair Value, Measurements, Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1) | Redeemable Preferred Stocks |  |  |  |  |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |  |  |  |
Fixed maturities at fair value | 0 |  | 0 |  |  |  |  |
Fair Value, Measurements, Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1) | Redeemable Preferred Stocks |  |  |  |  |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |  |  |  |
Fixed maturities at fair value |  |  |  |  |  | 0 |  |
Fair Value, Measurements, Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1) | Collateralized Loan Obligations |  |  |  |  |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |  |  |  |
Fixed maturities at fair value | 0 |  | 0 |  |  | 0 |  |
Fair Value, Measurements, Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1) | Other Mortgage- and Asset-backed |  |  |  |  |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |  |  |  |
Fixed maturities at fair value | 0 |  | 0 |  |  | 0 |  |
Fair Value, Measurements, Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1) | Equity Securities |  |  |  |  |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |  |  |  |
Equity securities | 7,900,000 |  | 7,900,000 |  |  | 13,400,000 |  |
Fair Value, Measurements, Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1) | Exchange Traded Funds |  |  |  |  |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |  |  |  |
Equity securities | 7,100,000 |  | 7,100,000 |  |  | 12,200,000 |  |
Fair Value, Measurements, Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1) | Limited Liability Companies and Limited Partnerships |  |  |  |  |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |  |  |  |
Equity securities | 0 |  | 0 |  |  | 0 |  |
Fair Value, Measurements, Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1) | Designated as Hedging Instrument |  |  |  |  |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |  |  |  |
Derivative Liability | 0 |  | 0 |  |  | 0 |  |
Fair Value, Measurements, Recurring | Significant Other Observable Inputs (Level 2) |  |  |  |  |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |  |  |  |
Convertible debt at fair value | 45,900,000 |  | 45,900,000 |  |  | 43,300,000 |  |
Total Assets | 6,260,400,000 |  | 6,260,400,000 |  |  | 6,646,900,000 |  |
Derivative Asset |  |  |  |  |  | 1,700,000 |  |
Derivative Liability | 15,600,000 |  | 15,600,000 |  |  | (400,000) |  |
Liabilities, Fair Value Disclosure | (15,600,000) |  | (15,600,000) |  |  | (400,000) |  |
Fair Value, Measurements, Recurring | Significant Other Observable Inputs (Level 2) | Investments in Fixed Maturities |  |  |  |  |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |  |  |  |
Fixed maturities at fair value | 6,186,200,000 |  | 6,186,200,000 |  |  | 6,563,300,000 |  |
Fair Value, Measurements, Recurring | Significant Other Observable Inputs (Level 2) | U.S. Government and Government Agencies and Authorities |  |  |  |  |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |  |  |  |
Fixed maturities at fair value | 392,800,000 |  | 392,800,000 |  |  | 424,400,000 |  |
Fair Value, Measurements, Recurring | Significant Other Observable Inputs (Level 2) | States and Political Subdivisions |  |  |  |  |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |  |  |  |
Fixed maturities at fair value | 1,320,100,000 |  | 1,320,100,000 |  |  | 1,568,900,000 |  |
Fair Value, Measurements, Recurring | Significant Other Observable Inputs (Level 2) | Foreign Governments |  |  |  |  |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |  |  |  |
Fixed maturities at fair value | 4,200,000 |  | 4,200,000 |  |  | 4,100,000 |  |
Fair Value, Measurements, Recurring | Significant Other Observable Inputs (Level 2) | Bonds and Notes |  |  |  |  |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |  |  |  |
Fixed maturities at fair value | 3,212,000,000 |  | 3,212,000,000 |  |  | 3,323,400,000 |  |
Fair Value, Measurements, Recurring | Significant Other Observable Inputs (Level 2) | Redeemable Preferred Stocks |  |  |  |  |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |  |  |  |
Fixed maturities at fair value | 1,200,000 |  | 1,200,000 |  |  |  |  |
Fair Value, Measurements, Recurring | Significant Other Observable Inputs (Level 2) | Redeemable Preferred Stocks |  |  |  |  |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |  |  |  |
Fixed maturities at fair value |  |  |  |  |  | 1,200,000 |  |
Fair Value, Measurements, Recurring | Significant Other Observable Inputs (Level 2) | Collateralized Loan Obligations |  |  |  |  |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |  |  |  |
Fixed maturities at fair value | 956,200,000 |  | 956,200,000 |  |  | 953,900,000 |  |
Fair Value, Measurements, Recurring | Significant Other Observable Inputs (Level 2) | Other Mortgage- and Asset-backed |  |  |  |  |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |  |  |  |
Fixed maturities at fair value | 299,700,000 |  | 299,700,000 |  |  | 287,400,000 |  |
Fair Value, Measurements, Recurring | Significant Other Observable Inputs (Level 2) | Equity Securities |  |  |  |  |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |  |  |  |
Equity securities | 28,300,000 |  | 28,300,000 |  |  | 38,600,000 |  |
Fair Value, Measurements, Recurring | Significant Other Observable Inputs (Level 2) | Exchange Traded Funds |  |  |  |  |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |  |  |  |
Equity securities | 0 |  | 0 |  |  | 0 |  |
Fair Value, Measurements, Recurring | Significant Other Observable Inputs (Level 2) | Limited Liability Companies and Limited Partnerships |  |  |  |  |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |  |  |  |
Equity securities | 0 |  | 0 |  |  | 0 |  |
Fair Value, Measurements, Recurring | Significant Unobservable Inputs (Level 3) |  |  |  |  |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |  |  |  |
Convertible debt at fair value | 0 |  | 0 |  |  | 0 |  |
Total Assets | 197,600,000 |  | 197,600,000 |  |  | 230,000,000.0 |  |
Derivative Asset |  |  |  |  |  | 0 |  |
Liabilities, Fair Value Disclosure | 0 |  | 0 |  |  | 0 |  |
Fair Value, Measurements, Recurring | Significant Unobservable Inputs (Level 3) | Investments in Fixed Maturities |  |  |  |  |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |  |  |  |
Fixed maturities at fair value | 193,900,000 |  | 193,900,000 |  |  | 227,900,000 |  |
Fair Value, Measurements, Recurring | Significant Unobservable Inputs (Level 3) | U.S. Government and Government Agencies and Authorities |  |  |  |  |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |  |  |  |
Fixed maturities at fair value | 0 |  | 0 |  |  | 0 |  |
Fair Value, Measurements, Recurring | Significant Unobservable Inputs (Level 3) | States and Political Subdivisions |  |  |  |  |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |  |  |  |
Fixed maturities at fair value | 100,000 |  | 100,000 |  |  | 0 |  |
Fair Value, Measurements, Recurring | Significant Unobservable Inputs (Level 3) | Foreign Governments |  |  |  |  |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |  |  |  |
Fixed maturities at fair value | 0 |  | 0 |  |  | 0 |  |
Fair Value, Measurements, Recurring | Significant Unobservable Inputs (Level 3) | Bonds and Notes |  |  |  |  |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |  |  |  |
Fixed maturities at fair value | 182,400,000 |  | 182,400,000 |  |  | 216,000,000.0 |  |
Fair Value, Measurements, Recurring | Significant Unobservable Inputs (Level 3) | Redeemable Preferred Stocks |  |  |  |  |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |  |  |  |
Fixed maturities at fair value | 6,600,000 |  | 6,600,000 |  |  |  |  |
Fair Value, Measurements, Recurring | Significant Unobservable Inputs (Level 3) | Redeemable Preferred Stocks |  |  |  |  |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |  |  |  |
Fixed maturities at fair value |  |  |  |  |  | 6,800,000 |  |
Fair Value, Measurements, Recurring | Significant Unobservable Inputs (Level 3) | Collateralized Loan Obligations |  |  |  |  |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |  |  |  |
Fixed maturities at fair value | 0 |  | 0 |  |  | 0 |  |
Fair Value, Measurements, Recurring | Significant Unobservable Inputs (Level 3) | Other Mortgage- and Asset-backed |  |  |  |  |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |  |  |  |
Fixed maturities at fair value | 4,800,000 |  | 4,800,000 |  |  | 5,100,000 |  |
Fair Value, Measurements, Recurring | Significant Unobservable Inputs (Level 3) | Equity Securities |  |  |  |  |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |  |  |  |
Equity securities | 3,700,000 |  | 3,700,000 |  |  | 2,100,000 |  |
Fair Value, Measurements, Recurring | Significant Unobservable Inputs (Level 3) | Exchange Traded Funds |  |  |  |  |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |  |  |  |
Equity securities | 0 |  | 0 |  |  | 0 |  |
Fair Value, Measurements, Recurring | Significant Unobservable Inputs (Level 3) | Limited Liability Companies and Limited Partnerships |  |  |  |  |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |  |  |  |
Equity securities | 0 |  | 0 |  |  | 0 |  |
Fair Value, Measurements, Recurring | Significant Unobservable Inputs (Level 3) | Designated as Hedging Instrument |  |  |  |  |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |  |  |  |
Derivative Liability | 0 |  | 0 |  |  | 0 |  |
Finance, Insurance and Real Estate | Fair Value, Measurements, Recurring | Preferred Stocks |  |  |  |  |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |  |  |  |
Equity securities | 19,900,000 |  | 19,900,000 |  |  | 29,000,000.0 |  |
Finance, Insurance and Real Estate | Fair Value, Measurements, Recurring | Common Stock |  |  |  |  |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |  |  |  |
Equity securities | 600,000 |  | 600,000 |  |  | 900,000 |  |
Finance, Insurance and Real Estate | Fair Value, Measurements, Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1) | Preferred Stocks |  |  |  |  |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |  |  |  |
Equity securities | 0 |  | 0 |  |  | 0 |  |
Finance, Insurance and Real Estate | Fair Value, Measurements, Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1) | Common Stock |  |  |  |  |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |  |  |  |
Equity securities | 600,000 |  | 600,000 |  |  | 900,000 |  |
Finance, Insurance and Real Estate | Fair Value, Measurements, Recurring | Significant Other Observable Inputs (Level 2) | Preferred Stocks |  |  |  |  |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |  |  |  |
Equity securities | 19,900,000 |  | 19,900,000 |  |  | 29,000,000.0 |  |
Finance, Insurance and Real Estate | Fair Value, Measurements, Recurring | Significant Other Observable Inputs (Level 2) | Common Stock |  |  |  |  |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |  |  |  |
Equity securities | 0 |  | 0 |  |  | 0 |  |
Finance, Insurance and Real Estate | Fair Value, Measurements, Recurring | Significant Unobservable Inputs (Level 3) | Preferred Stocks |  |  |  |  |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |  |  |  |
Equity securities | 0 |  | 0 |  |  | 0 |  |
Finance, Insurance and Real Estate | Fair Value, Measurements, Recurring | Significant Unobservable Inputs (Level 3) | Common Stock |  |  |  |  |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |  |  |  |
Equity securities | 0 |  | 0 |  |  | 0 |  |
Other Industries | Fair Value, Measurements, Recurring | Preferred Stocks |  |  |  |  |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |  |  |  |
Equity securities | 11,700,000 |  | 11,700,000 |  |  | 10,800,000 |  |
Other Industries | Fair Value, Measurements, Recurring | Common Stock |  |  |  |  |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |  |  |  |
Equity securities | 600,000 |  | 600,000 |  |  | 1,200,000 |  |
Other Industries | Fair Value, Measurements, Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1) | Preferred Stocks |  |  |  |  |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |  |  |  |
Equity securities | 0 |  | 0 |  |  | 0 |  |
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Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |  |  |  |
Equity securities | 200,000 |  | 200,000 |  |  | 300,000 |  |
Other Industries | Fair Value, Measurements, Recurring | Significant Other Observable Inputs (Level 2) | Preferred Stocks |  |  |  |  |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |  |  |  |
Equity securities | 8,400,000 |  | 8,400,000 |  |  | 9,200,000 |  |
Other Industries | Fair Value, Measurements, Recurring | Significant Other Observable Inputs (Level 2) | Common Stock |  |  |  |  |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |  |  |  |
Equity securities | 0 |  | 0 |  |  | 400,000 |  |
Other Industries | Fair Value, Measurements, Recurring | Significant Unobservable Inputs (Level 3) | Preferred Stocks |  |  |  |  |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |  |  |  |
Equity securities | 3,300,000 |  | 3,300,000 |  |  | 1,600,000 |  |
Other Industries | Fair Value, Measurements, Recurring | Significant Unobservable Inputs (Level 3) | Common Stock |  |  |  |  |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |  |  |  |
Equity securities | 400,000 |  | 400,000 |  |  | 500,000 |  |
Measured at Net Asset Value | Fair Value, Measurements, Recurring |  |  |  |  |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |  |  |  |
Convertible debt at fair value | 0 |  | 0 |  |  | 0 |  |
Total Assets | 193,500,000 |  | 193,500,000 |  |  | 189,100,000 |  |
Derivative Asset |  |  |  |  |  | 0 |  |
Liabilities, Fair Value Disclosure | 0 |  | 0 |  |  | 0 |  |
Measured at Net Asset Value | Fair Value, Measurements, Recurring | Investments in Fixed Maturities |  |  |  |  |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |  |  |  |
Fixed maturities at fair value | 0 |  | 0 |  |  | 0 |  |
Measured at Net Asset Value | Fair Value, Measurements, Recurring | U.S. Government and Government Agencies and Authorities |  |  |  |  |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |  |  |  |
Fixed maturities at fair value | 0 |  | 0 |  |  | 0 |  |
Measured at Net Asset Value | Fair Value, Measurements, Recurring | States and Political Subdivisions |  |  |  |  |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |  |  |  |
Fixed maturities at fair value | 0 |  | 0 |  |  | 0 |  |
Measured at Net Asset Value | Fair Value, Measurements, Recurring | Foreign Governments |  |  |  |  |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |  |  |  |
Fixed maturities at fair value | 0 |  | 0 |  |  | 0 |  |
Measured at Net Asset Value | Fair Value, Measurements, Recurring | Bonds and Notes |  |  |  |  |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |  |  |  |
Fixed maturities at fair value | 0 |  | 0 |  |  | 0 |  |
Measured at Net Asset Value | Fair Value, Measurements, Recurring | Redeemable Preferred Stocks |  |  |  |  |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |  |  |  |
Fixed maturities at fair value | 0 |  | 0 |  |  |  |  |
Measured at Net Asset Value | Fair Value, Measurements, Recurring | Redeemable Preferred Stocks |  |  |  |  |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |  |  |  |
Fixed maturities at fair value |  |  |  |  |  | 0 |  |
Measured at Net Asset Value | Fair Value, Measurements, Recurring | Collateralized Loan Obligations |  |  |  |  |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |  |  |  |
Fixed maturities at fair value | 0 |  | 0 |  |  | 0 |  |
Measured at Net Asset Value | Fair Value, Measurements, Recurring | Other Mortgage- and Asset-backed |  |  |  |  |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |  |  |  |
Fixed maturities at fair value | 0 |  | 0 |  |  | 0 |  |
Measured at Net Asset Value | Fair Value, Measurements, Recurring | Equity Securities |  |  |  |  |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |  |  |  |
Equity securities | 193,500,000 |  | 193,500,000 |  |  | 189,100,000 |  |
Measured at Net Asset Value | Fair Value, Measurements, Recurring | Exchange Traded Funds |  |  |  |  |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |  |  |  |
Equity securities | 0 |  | 0 |  |  | 0 |  |
Measured at Net Asset Value | Fair Value, Measurements, Recurring | Limited Liability Companies and Limited Partnerships |  |  |  |  |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |  |  |  |
Equity securities | 193,500,000 |  | 193,500,000 |  |  | 189,100,000 |  |
Measured at Net Asset Value | Fair Value, Measurements, Recurring | Designated as Hedging Instrument |  |  |  |  |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |  |  |  |
Derivative Liability | 0 |  | 0 |  |  | 0 |  |
Measured at Net Asset Value | Finance, Insurance and Real Estate | Fair Value, Measurements, Recurring | Preferred Stocks |  |  |  |  |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |  |  |  |
Equity securities | 0 |  | 0 |  |  | 0 |  |
Measured at Net Asset Value | Finance, Insurance and Real Estate | Fair Value, Measurements, Recurring | Common Stock |  |  |  |  |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |  |  |  |
Equity securities | 0 |  | 0 |  |  | 0 |  |
Measured at Net Asset Value | Other Industries | Fair Value, Measurements, Recurring | Preferred Stocks |  |  |  |  |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |  |  |  |
Equity securities | 0 |  | 0 |  |  | 0 |  |
Measured at Net Asset Value | Other Industries | Fair Value, Measurements, Recurring | Common Stock |  |  |  |  |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |  |  |  |
Equity securities | $ 0 |  | $ 0 |  |  | $ 0 |  |

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