Investments - Schedule of Securities in an Unrealized Loss Position Segregated by Type and Length of Time in an Unrealized Loss Position (Details) - USD ($) $ in Thousands	Dec. 31, 2022	Dec. 31, 2021
Fair value
Less than 12 months	$ 1,619,637	$ 642,717
12 months and greater	794,880	135,459
Total Fair Value	2,414,517	778,176
Amortized Cost
Amortized cost, less than 12 months	1,715,942	654,184
12 months and greater	978,797	140,883
Total Cost or Amortized Cost	2,694,739	795,067
Unrealized Loss
Less than 12 months	(96,305)	(11,467)
12 months and greater	(183,917)	(5,424)
Total Unrealized Loss	(280,222)	(16,891)
U.S. government
Fair value
Less than 12 months	399,361	2,942
12 months and greater	8,828
Total Fair Value	408,189	2,942
Amortized Cost
Amortized cost, less than 12 months	407,340	2,986
12 months and greater	9,720
Total Cost or Amortized Cost	417,060	2,986
Unrealized Loss
Less than 12 months	(7,979)	(44)
12 months and greater	(892)
Total Unrealized Loss	(8,871)	(44)
U.S. Agency
Fair value
Less than 12 months	32,987	1,498
12 months and greater	2,170
Total Fair Value	35,157	1,498
Amortized Cost
Amortized cost, less than 12 months	34,627	1,515
12 months and greater	2,567
Total Cost or Amortized Cost	37,194	1,515
Unrealized Loss
Less than 12 months	(1,640)	(17)
12 months and greater	(397)
Total Unrealized Loss	(2,037)	(17)
Non-U.S. government & agency
Fair value
Less than 12 months	3,626	4,346
12 months and greater	2,221
Total Fair Value	5,847	4,346
Amortized Cost
Amortized cost, less than 12 months	3,798	4,500
12 months and greater	3,000
Total Cost or Amortized Cost	6,798	4,500
Unrealized Loss
Less than 12 months	(172)	(154)
12 months and greater	(779)
Total Unrealized Loss	(951)	(154)
Agency MBS
Fair value
Less than 12 months	197,252	102,145
12 months and greater	117,851	62,669
Total Fair Value	315,103	164,814
Amortized Cost
Amortized cost, less than 12 months	212,776	104,336
12 months and greater	144,544	65,429
Total Cost or Amortized Cost	357,320	169,765
Unrealized Loss
Less than 12 months	(15,524)	(2,191)
12 months and greater	(26,693)	(2,760)
Total Unrealized Loss	(42,217)	(4,951)
ABS/CMBS/MBS
Fair value
Less than 12 months	96,754	150,997
12 months and greater	136,149	3,935
Total Fair Value	232,903	154,932
Amortized Cost
Amortized cost, less than 12 months	104,724	153,235
12 months and greater	163,623	4,036
Total Cost or Amortized Cost	268,347	157,271
Unrealized Loss
Less than 12 months	(7,970)	(2,238)
12 months and greater	(27,474)	(101)
Total Unrealized Loss	(35,444)	(2,339)
Corporate Debt
Fair value
Less than 12 months	660,830	217,791
12 months and greater	323,337	53,818
Total Fair Value	984,167	271,609
Amortized Cost
Amortized cost, less than 12 months	697,437	221,010
12 months and greater	374,707	55,704
Total Cost or Amortized Cost	1,072,144	276,714
Unrealized Loss
Less than 12 months	(36,607)	(3,219)
12 months and greater	(51,370)	(1,886)
Total Unrealized Loss	(87,977)	(5,105)
Municipal
Fair value
Less than 12 months	228,827	162,998
12 months and greater	204,324	15,037
Total Fair Value	433,151	178,035
Amortized Cost
Amortized cost, less than 12 months	255,240	166,602
12 months and greater	280,636	15,714
Total Cost or Amortized Cost	535,876	182,316
Unrealized Loss
Less than 12 months	(26,413)	(3,604)
12 months and greater	(76,312)	(677)
Total Unrealized Loss	$ (102,725)	$ (4,281)