Investments - Schedule of Fair Value and Gross Pre-Tax Net Unrealized Loss of Securities By Length of Time (Details) - USD ($) $ in Thousands	Jun. 30, 2024	Dec. 31, 2023
U.S. government and government agencies
Debt Securities, Available-for-Sale, Unrealized Loss Position [Line Items]
AFS Fair Value, Less than 12 Months	$ 33,667	$ 77,698
AFS Unrealized Losses, Less than 12 months	(52)	(188)
AFS Fair Value, 12 months or longer	107,306	108,578
AFS Unrealized Losses, 12 months or longer	(19,855)	(18,073)
AFS Fair Value	140,973	186,276
AFS Unrealized Losses	(19,907)	(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	9,234	8,251
AFS Unrealized Losses, 12 months or longer	(1,427)	(1,215)
AFS Fair Value	9,234	9,803
AFS Unrealized Losses	(1,427)	(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	128,665	137,031
AFS Unrealized Losses, Less than 12 months	(1,644)	(962)
AFS Fair Value, 12 months or longer	329,528	290,964
AFS Unrealized Losses, 12 months or longer	(31,507)	(27,965)
AFS Fair Value	458,193	427,995
AFS Unrealized Losses	(33,151)	(28,927)
Corporate securities
Debt Securities, Available-for-Sale, Unrealized Loss Position [Line Items]
AFS Fair Value, Less than 12 Months	358,779	263,423
AFS Unrealized Losses, Less than 12 months	(3,477)	(6,369)
AFS Fair Value, 12 months or longer	1,477,738	1,439,422
AFS Unrealized Losses, 12 months or longer	(140,248)	(131,519)
AFS Fair Value	1,836,517	1,702,845
AFS Unrealized Losses	(143,725)	(137,888)
CLO and other ABS
Debt Securities, Available-for-Sale, Unrealized Loss Position [Line Items]
AFS Fair Value, Less than 12 Months	368,307	278,940
AFS Unrealized Losses, Less than 12 months	(6,432)	(7,120)
AFS Fair Value, 12 months or longer	798,783	984,175
AFS Unrealized Losses, 12 months or longer	(63,472)	(78,885)
AFS Fair Value	1,167,090	1,263,115
AFS Unrealized Losses	(69,904)	(86,005)
RMBS
Debt Securities, Available-for-Sale, Unrealized Loss Position [Line Items]
AFS Fair Value, Less than 12 Months	385,794	351,976
AFS Unrealized Losses, Less than 12 months	(6,133)	(4,765)
AFS Fair Value, 12 months or longer	878,915	757,914
AFS Unrealized Losses, 12 months or longer	(105,287)	(81,086)
AFS Fair Value	1,264,709	1,109,890
AFS Unrealized Losses	(111,420)	(85,851)
CMBS
Debt Securities, Available-for-Sale, Unrealized Loss Position [Line Items]
AFS Fair Value, Less than 12 Months	75,052	130,189
AFS Unrealized Losses, Less than 12 months	(779)	(2,995)
AFS Fair Value, 12 months or longer	550,901	471,256
AFS Unrealized Losses, 12 months or longer	(38,599)	(42,135)
AFS Fair Value	625,953	601,445
AFS Unrealized Losses	(39,378)	(45,130)
Available-for-Sale Securities
Debt Securities, Available-for-Sale, Unrealized Loss Position [Line Items]
AFS Fair Value, Less than 12 Months	1,350,264	1,240,809
AFS Unrealized Losses, Less than 12 months	(18,517)	(22,486)
AFS Fair Value, 12 months or longer	4,152,405	4,060,560
AFS Unrealized Losses, 12 months or longer	(400,395)	(380,878)
AFS Fair Value	5,502,669	5,301,369
AFS Unrealized Losses	$ (418,912)	$ (403,364)