Investments - Securities in an Unrealized Loss Position Segregated by Type and Length of Time in an Unrealized Loss Position (Details) - USD ($) $ in Thousands	Mar. 31, 2026	Dec. 31, 2025
Fair value
Less than 12 months	$ 1,165,564	$ 303,929
12 months and greater	1,187,480	1,356,745
Total Fair Value	2,353,044	1,660,674
Amortized Cost
Amortized cost, less than 12 months	1,178,696	306,596
12 months and greater	1,330,557	1,494,513
Total Amortized Cost	2,509,253	1,801,109
Unrealized Loss
Less than 12 months	(13,132)	(2,667)
12 months and greater	(143,077)	(137,768)
Total Unrealized Loss	(156,209)	(140,435)
U.S. government
Fair value
Less than 12 months	13,965	8,610
12 months and greater	61,176	80,088
Total Fair Value	75,141	88,698
Amortized Cost
Amortized cost, less than 12 months	14,113	8,620
12 months and greater	62,084	80,997
Total Amortized Cost	76,197	89,617
Unrealized Loss
Less than 12 months	(148)	(10)
12 months and greater	(908)	(909)
Total Unrealized Loss	(1,056)	(919)
U.S. Agency
Fair value
Less than 12 months	7,741
12 months and greater	8,934	19,797
Total Fair Value	16,675	19,797
Amortized Cost
Amortized cost, less than 12 months	7,923
12 months and greater	9,008	19,926
Total Amortized Cost	16,931	19,926
Unrealized Loss
Less than 12 months	(182)
12 months and greater	(74)	(129)
Total Unrealized Loss	(256)	(129)
Non-U.S. government
Fair value
Less than 12 months	7,210
12 months and greater	4,204	4,244
Total Fair Value	11,414	4,244
Amortized Cost
Amortized cost, less than 12 months	7,310
12 months and greater	4,802	4,802
Total Amortized Cost	12,112	4,802
Unrealized Loss
Less than 12 months	(100)
12 months and greater	(598)	(558)
Total Unrealized Loss	(698)	(558)
Agency MBS
Fair value
Less than 12 months	238,880	34,783
12 months and greater	197,811	239,581
Total Fair Value	436,691	274,364
Amortized Cost
Amortized cost, less than 12 months	241,035	34,917
12 months and greater	226,470	267,839
Total Amortized Cost	467,505	302,756
Unrealized Loss
Less than 12 months	(2,155)	(134)
12 months and greater	(28,659)	(28,258)
Total Unrealized Loss	(30,814)	(28,392)
ABS/CMBS/MBS
Fair value
Less than 12 months	354,186	110,600
12 months and greater	136,541	142,903
Total Fair Value	490,727	253,503
Amortized Cost
Amortized cost, less than 12 months	356,597	110,826
12 months and greater	151,784	157,989
Total Amortized Cost	508,381	268,815
Unrealized Loss
Less than 12 months	(2,411)	(226)
12 months and greater	(15,243)	(15,086)
Total Unrealized Loss	(17,654)	(15,312)
Corporate
Fair value
Less than 12 months	517,300	146,177
12 months and greater	477,322	545,897
Total Fair Value	994,622	692,074
Amortized Cost
Amortized cost, less than 12 months	525,093	148,444
12 months and greater	508,114	571,560
Total Amortized Cost	1,033,207	720,004
Unrealized Loss
Less than 12 months	(7,793)	(2,267)
12 months and greater	(30,792)	(25,663)
Total Unrealized Loss	(38,585)	(27,930)
Municipal
Fair value
Less than 12 months	26,282	3,759
12 months and greater	301,492	324,235
Total Fair Value	327,774	327,994
Amortized Cost
Amortized cost, less than 12 months	26,625	3,789
12 months and greater	368,295	391,400
Total Amortized Cost	394,920	395,189
Unrealized Loss
Less than 12 months	(343)	(30)
12 months and greater	(66,803)	(67,165)
Total Unrealized Loss	$ (67,146)	$ (67,195)