Investments - Additional Information (Details) - USD ($) $ in Thousands	Jun. 30, 2024	Dec. 31, 2023	Jun. 30, 2023
Schedule of Investments [Line Items]
Debt Securities, Available-for-sale, Allowance for Credit Loss	$ 3,000	$ 3,000	$ 1,000
Securities fair value	29,000	24,000
Debt Securities, Available-for-sale, Unrealized Loss Position	1,159,000	1,032,000
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax	78,000	71,000
Debt Securities, Available for sale, Unrealized Loss Position, Accumulated Loss, Including Pledged Securities	$ 1,184,000
Average Percentage of Unrealized Loss Versus Amortized Cost for Below Investment Grade Securities	8.00%
Average Percentage of Unrealized Loss Versus Amortized Cost for Investment Grade Securities	7.00%
Fiduciary Funds Held by Insurance Distribution Subsidiaries	$ 2,000	2,000
Investment Portfolio [Member]
Schedule of Investments [Line Items]
Fair Value of Cash and Securities Pledged to Derivative Counterparties	25,000	27,000
Fixed Income Securities [Member]
Schedule of Investments [Line Items]
Debt Securities, Available-for-sale, Allowance for Credit Loss	3,000	3,000
Debt Securities, Available-for-sale, Unrealized Loss Position	1,113,000	1,028,000
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax	77,000	71,000
Fixed Income Securities [Member] | Corporate Debt Securities [Member]
Schedule of Investments [Line Items]
Debt Securities, Available-for-sale, Allowance for Credit Loss	0	0
Debt Securities, Available-for-sale, Unrealized Loss Position	618,000	584,000
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax	46,000	44,000
Fixed Income Securities [Member] | Corporate Debt Securities [Member] | External Credit Rating, Investment Grade
Schedule of Investments [Line Items]
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax	45,000
Fixed Income Securities [Member] | Corporate Debt Securities [Member] | External Credit Rating, Non Investment Grade [Member]
Schedule of Investments [Line Items]
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax	483
Fixed Income Securities [Member] | Residential Mortgage-Backed Securities [Member]
Schedule of Investments [Line Items]
Debt Securities, Available-for-sale, Allowance for Credit Loss	3,000	3,000
Debt Securities, Available-for-sale, Unrealized Loss Position	129,000	104,000
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax	13,000	14,000
Fixed Income Securities [Member] | Asset-backed Securities [Member]
Schedule of Investments [Line Items]
Debt Securities, Available-for-sale, Allowance for Credit Loss	0	0
Debt Securities, Available-for-sale, Unrealized Loss Position	117,000	92,000
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax	5,000	1,000
Reported Value Measurement [Member]
Schedule of Investments [Line Items]
Other investments	153,000	77,000
Reported Value Measurement [Member] | Interest Rate Contract [Member]
Schedule of Investments [Line Items]
Other investments	$ 89,000	$ 39,000