Investments - Schedule of Fixed Maturities Available for Sale by Component (Details) - USD ($) $ in Thousands	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	$ 18,835,809	$ 18,924,914
Allowance for Credit Losses	(10,395)	(7,115)
Gross Unrealized Gains	254,587	451,764
Gross Unrealized Losses	(1,924,989)	(1,499,357)
Fair value	$ 17,155,012	$ 17,870,206
Percentage of total fixed maturities (as a percent)	100.00%	100.00%
U.S. Government direct, guaranteed, and government-sponsored enterprises
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	$ 401,753	$ 398,450
Allowance for Credit Losses	0	0
Gross Unrealized Gains	1	7
Gross Unrealized Losses	(42,794)	(32,306)
Fair value	$ 358,960	$ 366,151
Percentage of total fixed maturities (as a percent)	2.00%	2.00%
States, municipalities, and political subdivisions
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	$ 3,300,901	$ 3,296,305
Allowance for Credit Losses	0	0
Gross Unrealized Gains	20,662	47,346
Gross Unrealized Losses	(534,759)	(403,329)
Fair value	$ 2,786,804	$ 2,940,322
Percentage of total fixed maturities (as a percent)	16.00%	16.00%
Foreign governments
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	$ 36,883	$ 44,453
Allowance for Credit Losses	0	0
Gross Unrealized Gains	18	1
Gross Unrealized Losses	(8,870)	(10,348)
Fair value	$ 28,031	$ 34,106
Percentage of total fixed maturities (as a percent)	0.00%	0.00%
Corporates
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	$ 14,976,815	$ 15,062,244
Allowance for Credit Losses	(7,098)	(7,115)	$ 0
Gross Unrealized Gains	227,924	399,371
Gross Unrealized Losses	(1,336,380)	(1,049,317)
Fair value	$ 13,861,261	$ 14,405,183
Percentage of total fixed maturities (as a percent)	81.00%	81.00%
Corporates | Industrials
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	$ 7,889,074	$ 8,016,126
Allowance for Credit Losses	(7,098)	(7,115)
Gross Unrealized Gains	105,610	213,078
Gross Unrealized Losses	(805,330)	(566,847)
Fair value	$ 7,182,256	$ 7,655,242
Percentage of total fixed maturities (as a percent)	42.00%	43.00%
Corporates | Financial
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	$ 5,006,375	$ 5,028,151
Allowance for Credit Losses	0	0
Gross Unrealized Gains	82,598	112,368
Gross Unrealized Losses	(413,043)	(388,340)
Fair value	$ 4,675,930	$ 4,752,179
Percentage of total fixed maturities (as a percent)	27.00%	27.00%
Corporates | Utilities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	$ 2,081,366	$ 2,017,967
Allowance for Credit Losses	0	0
Gross Unrealized Gains	39,716	73,925
Gross Unrealized Losses	(118,007)	(94,130)
Fair value	$ 2,003,075	$ 1,997,762
Percentage of total fixed maturities (as a percent)	12.00%	11.00%
Collateralized debt obligations
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	$ 36,923	$ 37,110
Allowance for Credit Losses	0	0
Gross Unrealized Gains	5,943	5,036
Gross Unrealized Losses	0	0
Fair value	$ 42,866	$ 42,146
Percentage of total fixed maturities (as a percent)	0.00%	0.00%
Other asset-backed securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	$ 82,534	$ 86,352
Allowance for Credit Losses	(3,297)	0
Gross Unrealized Gains	39	3
Gross Unrealized Losses	(2,186)	(4,057)
Fair value	$ 77,090	$ 82,298
Percentage of total fixed maturities (as a percent)	1.00%	1.00%