Investments - Schedule of Fair Value and Gross Pre-Tax Net Unrealized Loss of Securities By Length of Time (Details) - USD ($) $ in Thousands	Dec. 31, 2024	Dec. 31, 2023
Debt Securities, Available-for-Sale, Unrealized Loss Position [Line Items]
AFS Fair Value, Less than 12 Months	$ 2,101,944	$ 1,240,809
AFS Unrealized Losses, Less than 12 months	(45,680)	(22,486)
AFS Fair Value, 12 months or longer	3,141,858	4,060,560
AFS Unrealized Losses, 12 months or longer	(324,401)	(380,878)
AFS Fair Value	5,243,802	5,301,369
AFS Unrealized Losses	(370,081)	(403,364)
U.S. government and government agencies
Debt Securities, Available-for-Sale, Unrealized Loss Position [Line Items]
AFS Fair Value, Less than 12 Months	14,708	77,698
AFS Unrealized Losses, Less than 12 months	(70)	(188)
AFS Fair Value, 12 months or longer	105,326	108,578
AFS Unrealized Losses, 12 months or longer	(19,683)	(18,073)
AFS Fair Value	120,034	186,276
AFS Unrealized Losses	(19,753)	(18,261)
Foreign government
Debt Securities, Available-for-Sale, Unrealized Loss Position [Line Items]
AFS Fair Value, Less than 12 Months	0	1,552
AFS Unrealized Losses, Less than 12 months	0	(87)
AFS Fair Value, 12 months or longer	9,302	8,251
AFS Unrealized Losses, 12 months or longer	(1,333)	(1,215)
AFS Fair Value	9,302	9,803
AFS Unrealized Losses	(1,333)	(1,302)
Obligations of states and political subdivisions
Debt Securities, Available-for-Sale, Unrealized Loss Position [Line Items]
AFS Fair Value, Less than 12 Months	153,996	137,031
AFS Unrealized Losses, Less than 12 months	(3,539)	(962)
AFS Fair Value, 12 months or longer	247,735	290,964
AFS Unrealized Losses, 12 months or longer	(28,820)	(27,965)
AFS Fair Value	401,731	427,995
AFS Unrealized Losses	(32,359)	(28,927)
Corporate securities
Debt Securities, Available-for-Sale, Unrealized Loss Position [Line Items]
AFS Fair Value, Less than 12 Months	684,999	263,423
AFS Unrealized Losses, Less than 12 months	(11,699)	(6,369)
AFS Fair Value, 12 months or longer	1,083,392	1,439,422
AFS Unrealized Losses, 12 months or longer	(111,502)	(131,519)
AFS Fair Value	1,768,391	1,702,845
AFS Unrealized Losses	(123,201)	(137,888)
CLO and other ABS
Debt Securities, Available-for-Sale, Unrealized Loss Position [Line Items]
AFS Fair Value, Less than 12 Months	349,786	278,940
AFS Unrealized Losses, Less than 12 months	(6,296)	(7,120)
AFS Fair Value, 12 months or longer	601,057	984,175
AFS Unrealized Losses, 12 months or longer	(43,393)	(78,885)
AFS Fair Value	950,843	1,263,115
AFS Unrealized Losses	(49,689)	(86,005)
RMBS
Debt Securities, Available-for-Sale, Unrealized Loss Position [Line Items]
AFS Fair Value, Less than 12 Months	714,061	351,976
AFS Unrealized Losses, Less than 12 months	(21,206)	(4,765)
AFS Fair Value, 12 months or longer	677,574	757,914
AFS Unrealized Losses, 12 months or longer	(91,516)	(81,086)
AFS Fair Value	1,391,635	1,109,890
AFS Unrealized Losses	(112,722)	(85,851)
CMBS
Debt Securities, Available-for-Sale, Unrealized Loss Position [Line Items]
AFS Fair Value, Less than 12 Months	184,394	130,189
AFS Unrealized Losses, Less than 12 months	(2,870)	(2,995)
AFS Fair Value, 12 months or longer	417,472	471,256
AFS Unrealized Losses, 12 months or longer	(28,154)	(42,135)
AFS Fair Value	601,866	601,445
AFS Unrealized Losses	$ (31,024)	$ (45,130)

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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