Investments - Schedule of Fair Value and Gross Pre-Tax Net Unrealized Loss of Securities By Length of Time (Details) - USD ($) $ in Thousands	Mar. 31, 2025	Dec. 31, 2024
Debt Securities, Available-for-Sale, Unrealized Loss Position [Line Items]
AFS Fair Value, Less than 12 Months	$ 1,782,171	$ 2,101,944
AFS Unrealized Losses, Less than 12 months	(27,058)	(45,680)
AFS Fair Value, 12 months or longer	2,987,394	3,141,858
AFS Unrealized Losses, 12 months or longer	(280,404)	(324,401)
AFS Fair Value	4,769,565	5,243,802
AFS Unrealized Losses	(307,462)	(370,081)
U.S. government and government agencies
Debt Securities, Available-for-Sale, Unrealized Loss Position [Line Items]
AFS Fair Value, Less than 12 Months	11,277	14,708
AFS Unrealized Losses, Less than 12 months	(41)	(70)
AFS Fair Value, 12 months or longer	108,507	105,326
AFS Unrealized Losses, 12 months or longer	(16,558)	(19,683)
AFS Fair Value	119,784	120,034
AFS Unrealized Losses	(16,599)	(19,753)
Foreign government
Debt Securities, Available-for-Sale, Unrealized Loss Position [Line Items]
AFS Fair Value, Less than 12 Months	0	0
AFS Unrealized Losses, Less than 12 months	0	0
AFS Fair Value, 12 months or longer	9,471	9,302
AFS Unrealized Losses, 12 months or longer	(1,150)	(1,333)
AFS Fair Value	9,471	9,302
AFS Unrealized Losses	(1,150)	(1,333)
Obligations of states and political subdivisions
Debt Securities, Available-for-Sale, Unrealized Loss Position [Line Items]
AFS Fair Value, Less than 12 Months	122,534	153,996
AFS Unrealized Losses, Less than 12 months	(2,103)	(3,539)
AFS Fair Value, 12 months or longer	236,649	247,735
AFS Unrealized Losses, 12 months or longer	(28,541)	(28,820)
AFS Fair Value	359,183	401,731
AFS Unrealized Losses	(30,644)	(32,359)
Corporate securities
Debt Securities, Available-for-Sale, Unrealized Loss Position [Line Items]
AFS Fair Value, Less than 12 Months	441,777	684,999
AFS Unrealized Losses, Less than 12 months	(5,535)	(11,699)
AFS Fair Value, 12 months or longer	1,021,950	1,083,392
AFS Unrealized Losses, 12 months or longer	(95,345)	(111,502)
AFS Fair Value	1,463,727	1,768,391
AFS Unrealized Losses	(100,880)	(123,201)
CLO and other ABS
Debt Securities, Available-for-Sale, Unrealized Loss Position [Line Items]
AFS Fair Value, Less than 12 Months	507,154	349,786
AFS Unrealized Losses, Less than 12 months	(7,615)	(6,296)
AFS Fair Value, 12 months or longer	555,377	601,057
AFS Unrealized Losses, 12 months or longer	(39,058)	(43,393)
AFS Fair Value	1,062,531	950,843
AFS Unrealized Losses	(46,673)	(49,689)
RMBS
Debt Securities, Available-for-Sale, Unrealized Loss Position [Line Items]
AFS Fair Value, Less than 12 Months	589,388	714,061
AFS Unrealized Losses, Less than 12 months	(10,728)	(21,206)
AFS Fair Value, 12 months or longer	668,360	677,574
AFS Unrealized Losses, 12 months or longer	(77,493)	(91,516)
AFS Fair Value	1,257,748	1,391,635
AFS Unrealized Losses	(88,221)	(112,722)
CMBS
Debt Securities, Available-for-Sale, Unrealized Loss Position [Line Items]
AFS Fair Value, Less than 12 Months	110,041	184,394
AFS Unrealized Losses, Less than 12 months	(1,036)	(2,870)
AFS Fair Value, 12 months or longer	387,080	417,472
AFS Unrealized Losses, 12 months or longer	(22,259)	(28,154)
AFS Fair Value	497,121	601,866
AFS Unrealized Losses	$ (23,295)	$ (31,024)

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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