Investments - Schedule of Fair Value and Gross Pre-Tax Net Unrealized Loss of Securities By Length of Time (Details) - USD ($) $ in Thousands	Jun. 30, 2025	Dec. 31, 2024
Debt Securities, Available-for-Sale, Unrealized Loss Position [Line Items]
AFS Fair Value, Less than 12 Months	$ 1,352,011	$ 2,101,944
AFS Unrealized Losses, Less than 12 months	(25,413)	(45,680)
AFS Fair Value, 12 months or longer	2,827,944	3,141,858
AFS Unrealized Losses, 12 months or longer	(256,673)	(324,401)
AFS Fair Value	4,179,955	5,243,802
AFS Unrealized Losses	(282,086)	(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	6,275	14,708
AFS Unrealized Losses, Less than 12 months	(40)	(70)
AFS Fair Value, 12 months or longer	108,474	105,326
AFS Unrealized Losses, 12 months or longer	(16,647)	(19,683)
AFS Fair Value	114,749	120,034
AFS Unrealized Losses	(16,687)	(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	9,592	9,302
AFS Unrealized Losses, 12 months or longer	(1,011)	(1,333)
AFS Fair Value	9,592	9,302
AFS Unrealized Losses	(1,011)	(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	155,940	153,996
AFS Unrealized Losses, Less than 12 months	(3,377)	(3,539)
AFS Fair Value, 12 months or longer	219,996	247,735
AFS Unrealized Losses, 12 months or longer	(29,485)	(28,820)
AFS Fair Value	375,936	401,731
AFS Unrealized Losses	(32,862)	(32,359)
Corporate securities
Debt Securities, Available-for-Sale, Unrealized Loss Position [Line Items]
AFS Fair Value, Less than 12 Months	243,575	684,999
AFS Unrealized Losses, Less than 12 months	(3,677)	(11,699)
AFS Fair Value, 12 months or longer	969,247	1,083,392
AFS Unrealized Losses, 12 months or longer	(84,239)	(111,502)
AFS Fair Value	1,212,822	1,768,391
AFS Unrealized Losses	(87,916)	(123,201)
CLO and other ABS
Debt Securities, Available-for-Sale, Unrealized Loss Position [Line Items]
AFS Fair Value, Less than 12 Months	330,552	349,786
AFS Unrealized Losses, Less than 12 months	(6,239)	(6,296)
AFS Fair Value, 12 months or longer	504,728	601,057
AFS Unrealized Losses, 12 months or longer	(32,512)	(43,393)
AFS Fair Value	835,280	950,843
AFS Unrealized Losses	(38,751)	(49,689)
RMBS
Debt Securities, Available-for-Sale, Unrealized Loss Position [Line Items]
AFS Fair Value, Less than 12 Months	557,024	714,061
AFS Unrealized Losses, Less than 12 months	(10,152)	(21,206)
AFS Fair Value, 12 months or longer	647,612	677,574
AFS Unrealized Losses, 12 months or longer	(74,621)	(91,516)
AFS Fair Value	1,204,636	1,391,635
AFS Unrealized Losses	(84,773)	(112,722)
CMBS
Debt Securities, Available-for-Sale, Unrealized Loss Position [Line Items]
AFS Fair Value, Less than 12 Months	58,645	184,394
AFS Unrealized Losses, Less than 12 months	(1,928)	(2,870)
AFS Fair Value, 12 months or longer	368,295	417,472
AFS Unrealized Losses, 12 months or longer	(18,158)	(28,154)
AFS Fair Value	426,940	601,866
AFS Unrealized Losses	$ (20,086)	$ (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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