Investments - Gross Unrealized Losses and Fair Value of Available for Sale Securities (Details) - USD ($) $ in Thousands	Dec. 31, 2024	Dec. 31, 2023
Debt Securities, Available-for-sale [Line Items]
Fair value, less than 12 months	$ 1,338,025	$ 381,388
Unrealized losses, less than 12 months	(30,838)	(4,567)
Fair value, 12 months or greater	2,781,382	3,981,258
Unrealized losses, 12 months or greater	(429,538)	(438,964)
Fair value, total	4,119,407	4,362,646
Unrealized losses, total	(460,376)	(443,531)
U.S. government and agency securities
Debt Securities, Available-for-sale [Line Items]
Fair value, less than 12 months	5,807	15,650
Unrealized losses, less than 12 months	(574)	(938)
Fair value, 12 months or greater	113,783	113,678
Unrealized losses, 12 months or greater	(31,603)	(25,953)
Fair value, total	119,590	129,328
Unrealized losses, total	(32,177)	(26,891)
State and municipal obligations
Debt Securities, Available-for-sale [Line Items]
Fair value, less than 12 months	45,539	17,154
Unrealized losses, less than 12 months	(2,399)	(551)
Fair value, 12 months or greater	78,523	104,949
Unrealized losses, 12 months or greater	(15,864)	(15,486)
Fair value, total	124,062	122,103
Unrealized losses, total	(18,263)	(16,037)
Corporate bonds and notes
Debt Securities, Available-for-sale [Line Items]
Fair value, less than 12 months	749,427	161,924
Unrealized losses, less than 12 months	(18,113)	(1,261)
Fair value, 12 months or greater	1,552,535	2,055,113
Unrealized losses, 12 months or greater	(259,422)	(257,916)
Fair value, total	2,301,962	2,217,037
Unrealized losses, total	(277,535)	(259,177)
RMBS
Debt Securities, Available-for-sale [Line Items]
Fair value, less than 12 months	296,899	113,506
Unrealized losses, less than 12 months	(6,467)	(1,439)
Fair value, 12 months or greater	559,525	653,955
Unrealized losses, 12 months or greater	(93,589)	(82,659)
Fair value, total	856,424	767,461
Unrealized losses, total	(100,056)	(84,098)
CMBS
Debt Securities, Available-for-sale [Line Items]
Fair value, less than 12 months	15,179	8,558
Unrealized losses, less than 12 months	(139)	(31)
Fair value, 12 months or greater	388,282	546,104
Unrealized losses, 12 months or greater	(26,052)	(46,666)
Fair value, total	403,461	554,662
Unrealized losses, total	(26,191)	(46,697)
CLO
Debt Securities, Available-for-sale [Line Items]
Fair value, less than 12 months	44,350	15,083
Unrealized losses, less than 12 months	(65)	(25)
Fair value, 12 months or greater	43,542	438,294
Unrealized losses, 12 months or greater	(784)	(6,528)
Fair value, total	87,892	453,377
Unrealized losses, total	(849)	(6,553)
Other ABS
Debt Securities, Available-for-sale [Line Items]
Fair value, less than 12 months	180,824	49,513
Unrealized losses, less than 12 months	(3,081)	(322)
Fair value, 12 months or greater	45,192	64,078
Unrealized losses, 12 months or greater	(2,224)	(3,715)
Fair value, total	226,016	113,591
Unrealized losses, total	$ (5,305)	(4,037)
Foreign government and agency securities
Debt Securities, Available-for-sale [Line Items]
Fair value, less than 12 months		0
Unrealized losses, less than 12 months		0
Fair value, 12 months or greater		5,087
Unrealized losses, 12 months or greater		(41)
Fair value, total		5,087
Unrealized losses, total		$ (41)