Investments - Schedule of Fixed Maturities Available for Sale by Component (Details) - USD ($) $ in Thousands	Dec. 31, 2025	Dec. 31, 2024	Dec. 31, 2023
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	$ 18,820,464	$ 18,835,809
Allowance for Credit Losses	(3,297)	(10,395)	$ (7,115)
Gross Unrealized Gains	409,982	254,587
Gross Unrealized Losses	(1,637,807)	(1,924,989)
Fair value	$ 17,589,342	$ 17,155,012
Percentage of total fixed maturities	100.00%	100.00%
U.S. Government direct, guaranteed, and government-sponsored enterprises
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	$ 409,170	$ 401,753
Allowance for Credit Losses	0	0
Gross Unrealized Gains	161	1
Gross Unrealized Losses	(25,478)	(42,794)
Fair value	$ 383,853	$ 358,960
Percentage of total fixed maturities	2.00%	2.00%
States, municipalities, and political subdivisions
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	$ 3,385,433	$ 3,300,901
Allowance for Credit Losses	0	0
Gross Unrealized Gains	26,955	20,662
Gross Unrealized Losses	(531,762)	(534,759)
Fair value	$ 2,880,626	$ 2,786,804
Percentage of total fixed maturities	16.00%	16.00%
Foreign governments
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	$ 47,448	$ 36,883
Allowance for Credit Losses	0	0
Gross Unrealized Gains	138	18
Gross Unrealized Losses	(8,040)	(8,870)
Fair value	$ 39,546	$ 28,031
Percentage of total fixed maturities	0.00%	0.00%
Corporates
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	$ 14,863,082	$ 14,976,815
Allowance for Credit Losses	0	(7,098)
Gross Unrealized Gains	380,851	227,924
Gross Unrealized Losses	(1,072,415)	(1,336,380)
Fair value	$ 14,171,518	$ 13,861,261
Percentage of total fixed maturities	81.00%	81.00%
Corporates | Industrials
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	$ 7,787,885	$ 7,889,074
Allowance for Credit Losses	0	(7,098)
Gross Unrealized Gains	175,164	105,610
Gross Unrealized Losses	(645,363)	(805,330)
Fair value	$ 7,317,686	$ 7,182,256
Percentage of total fixed maturities	42.00%	42.00%
Corporates | Financial
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	$ 4,982,187	$ 5,006,375
Allowance for Credit Losses	0	0
Gross Unrealized Gains	134,105	82,598
Gross Unrealized Losses	(333,966)	(413,043)
Fair value	$ 4,782,326	$ 4,675,930
Percentage of total fixed maturities	27.00%	27.00%
Corporates | Utilities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	$ 2,093,010	$ 2,081,366
Allowance for Credit Losses	0	0
Gross Unrealized Gains	71,582	39,716
Gross Unrealized Losses	(93,086)	(118,007)
Fair value	$ 2,071,506	$ 2,003,075
Percentage of total fixed maturities	12.00%	12.00%
Collateralized debt obligations
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	$ 0	$ 36,923
Allowance for Credit Losses	0	0
Gross Unrealized Gains	0	5,943
Gross Unrealized Losses	0	0
Fair value	$ 0	$ 42,866
Percentage of total fixed maturities	0.00%	0.00%
Other asset-backed securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	$ 115,331	$ 82,534
Allowance for Credit Losses	(3,297)	(3,297)
Gross Unrealized Gains	1,877	39
Gross Unrealized Losses	(112)	(2,186)
Fair value	$ 113,799	$ 77,090
Percentage of total fixed maturities	1.00%	1.00%