Investments - Gross Unrealized Losses and Fair Value of Available for Sale Securities (Details) - USD ($) $ in Thousands	Mar. 31, 2025	Dec. 31, 2024
Debt Securities, Available-for-sale [Line Items]
Fair value, less than 12 months	$ 961,400	$ 1,338,025
Unrealized losses, less than 12 months	(16,486)	(30,838)
Fair value, 12 months or greater	2,624,693	2,781,382
Unrealized losses, 12 months or greater	(381,000)	(429,538)
Fair value, total	3,586,093	4,119,407
Unrealized losses, total	(397,486)	(460,376)
U.S. government and agency securities
Debt Securities, Available-for-sale [Line Items]
Fair value, less than 12 months	19,797	5,807
Unrealized losses, less than 12 months	(397)	(574)
Fair value, 12 months or greater	113,454	113,783
Unrealized losses, 12 months or greater	(28,093)	(31,603)
Fair value, total	133,251	119,590
Unrealized losses, total	(28,490)	(32,177)
State and municipal obligations
Debt Securities, Available-for-sale [Line Items]
Fair value, less than 12 months	30,101	45,539
Unrealized losses, less than 12 months	(1,126)	(2,399)
Fair value, 12 months or greater	84,894	78,523
Unrealized losses, 12 months or greater	(14,695)	(15,864)
Fair value, total	114,995	124,062
Unrealized losses, total	(15,821)	(18,263)
Corporate bonds and notes
Debt Securities, Available-for-sale [Line Items]
Fair value, less than 12 months	496,187	749,427
Unrealized losses, less than 12 months	(10,138)	(18,113)
Fair value, 12 months or greater	1,434,951	1,552,535
Unrealized losses, 12 months or greater	(235,365)	(259,422)
Fair value, total	1,931,138	2,301,962
Unrealized losses, total	(245,503)	(277,535)
RMBS
Debt Securities, Available-for-sale [Line Items]
Fair value, less than 12 months	135,449	296,899
Unrealized losses, less than 12 months	(2,936)	(6,467)
Fair value, 12 months or greater	557,444	559,525
Unrealized losses, 12 months or greater	(79,912)	(93,589)
Fair value, total	692,893	856,424
Unrealized losses, total	(82,848)	(100,056)
CMBS
Debt Securities, Available-for-sale [Line Items]
Fair value, less than 12 months	18,806	15,179
Unrealized losses, less than 12 months	(103)	(139)
Fair value, 12 months or greater	369,433	388,282
Unrealized losses, 12 months or greater	(20,833)	(26,052)
Fair value, total	388,239	403,461
Unrealized losses, total	(20,936)	(26,191)
CLO
Debt Securities, Available-for-sale [Line Items]
Fair value, less than 12 months	128,603	44,350
Unrealized losses, less than 12 months	(267)	(65)
Fair value, 12 months or greater	29,699	43,542
Unrealized losses, 12 months or greater	(450)	(784)
Fair value, total	158,302	87,892
Unrealized losses, total	(717)	(849)
Other ABS
Debt Securities, Available-for-sale [Line Items]
Fair value, less than 12 months	132,457	180,824
Unrealized losses, less than 12 months	(1,519)	(3,081)
Fair value, 12 months or greater	34,818	45,192
Unrealized losses, 12 months or greater	(1,652)	(2,224)
Fair value, total	167,275	226,016
Unrealized losses, total	$ (3,171)	$ (5,305)