Investments - Gross Unrealized Losses and Fair Value of Available for Sale Securities (Details) - USD ($) $ in Thousands	Jun. 30, 2025	Dec. 31, 2024
Debt Securities, Available-for-sale [Line Items]
Fair value, less than 12 months	$ 680,544	$ 1,338,025
Unrealized losses, less than 12 months	(15,264)	(30,838)
Fair value, 12 months or greater	2,477,465	2,781,382
Unrealized losses, 12 months or greater	(363,361)	(429,538)
Fair value, total	3,158,009	4,119,407
Unrealized losses, total	(378,625)	(460,376)
U.S. government and agency securities
Debt Securities, Available-for-sale [Line Items]
Fair value, less than 12 months	4,696	5,807
Unrealized losses, less than 12 months	(532)	(574)
Fair value, 12 months or greater	112,687	113,783
Unrealized losses, 12 months or greater	(28,738)	(31,603)
Fair value, total	117,383	119,590
Unrealized losses, total	(29,270)	(32,177)
State and municipal obligations
Debt Securities, Available-for-sale [Line Items]
Fair value, less than 12 months	40,568	45,539
Unrealized losses, less than 12 months	(1,724)	(2,399)
Fair value, 12 months or greater	84,611	78,523
Unrealized losses, 12 months or greater	(14,651)	(15,864)
Fair value, total	125,179	124,062
Unrealized losses, total	(16,375)	(18,263)
Corporate bonds and notes
Debt Securities, Available-for-sale [Line Items]
Fair value, less than 12 months	312,136	749,427
Unrealized losses, less than 12 months	(7,899)	(18,113)
Fair value, 12 months or greater	1,362,178	1,552,535
Unrealized losses, 12 months or greater	(222,342)	(259,422)
Fair value, total	1,674,314	2,301,962
Unrealized losses, total	(230,241)	(277,535)
RMBS
Debt Securities, Available-for-sale [Line Items]
Fair value, less than 12 months	124,531	296,899
Unrealized losses, less than 12 months	(2,878)	(6,467)
Fair value, 12 months or greater	543,954	559,525
Unrealized losses, 12 months or greater	(77,741)	(93,589)
Fair value, total	668,485	856,424
Unrealized losses, total	(80,619)	(100,056)
CMBS
Debt Securities, Available-for-sale [Line Items]
Fair value, less than 12 months	8,280	15,179
Unrealized losses, less than 12 months	(75)	(139)
Fair value, 12 months or greater	304,678	388,282
Unrealized losses, 12 months or greater	(17,998)	(26,052)
Fair value, total	312,958	403,461
Unrealized losses, total	(18,073)	(26,191)
CLO
Debt Securities, Available-for-sale [Line Items]
Fair value, less than 12 months	99,329	44,350
Unrealized losses, less than 12 months	(228)	(65)
Fair value, 12 months or greater	35,728	43,542
Unrealized losses, 12 months or greater	(352)	(784)
Fair value, total	135,057	87,892
Unrealized losses, total	(580)	(849)
Other ABS
Debt Securities, Available-for-sale [Line Items]
Fair value, less than 12 months	91,004	180,824
Unrealized losses, less than 12 months	(1,928)	(3,081)
Fair value, 12 months or greater	33,629	45,192
Unrealized losses, 12 months or greater	(1,539)	(2,224)
Fair value, total	124,633	226,016
Unrealized losses, total	$ (3,467)	$ (5,305)