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
Other Industries | 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	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