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	Sep. 30, 2022	Dec. 31, 2021
Fair value
Less than 12 months	$ 1,852,501	$ 642,717
12 months and greater	470,782	135,459
Total Fair Value	2,323,283	778,176
Amortized Cost
Amortized cost, less than 12 months	2,043,103	654,184
12 months and greater	581,888	140,883
Total Cost or Amortized Cost	2,624,991	795,067
Unrealized Loss
Less than 12 months	(190,602)	(11,467)
12 months and greater	(111,106)	(5,424)
Total Unrealized Loss	(301,708)	(16,891)
U.S. government
Fair value
Less than 12 months	285,302	2,942
12 months and greater	5,315
Total Fair Value	290,617	2,942
Amortized Cost
Amortized cost, less than 12 months	293,829	2,986
12 months and greater	5,765
Total Cost or Amortized Cost	299,594	2,986
Unrealized Loss
Less than 12 months	(8,527)	(44)
12 months and greater	(450)
Total Unrealized Loss	(8,977)	(44)
U.S. Agency
Fair value
Less than 12 months	30,089	1,498
Total Fair Value	30,089	1,498
Amortized Cost
Amortized cost, less than 12 months	32,211	1,515
Total Cost or Amortized Cost	32,211	1,515
Unrealized Loss
Less than 12 months	(2,122)	(17)
Total Unrealized Loss	(2,122)	(17)
Non-U.S. government & agency
Fair value
Less than 12 months	3,594	4,346
12 months and greater	2,118
Total Fair Value	5,712	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	(204)	(154)
12 months and greater	(882)
Total Unrealized Loss	(1,086)	(154)
Agency MBS
Fair value
Less than 12 months	192,947	102,145
12 months and greater	112,457	62,669
Total Fair Value	305,404	164,814
Amortized Cost
Amortized cost, less than 12 months	210,448	104,336
12 months and greater	138,528	65,429
Total Cost or Amortized Cost	348,976	169,765
Unrealized Loss
Less than 12 months	(17,501)	(2,191)
12 months and greater	(26,071)	(2,760)
Total Unrealized Loss	(43,572)	(4,951)
ABS/CMBS/MBS
Fair value
Less than 12 months	148,272	150,997
12 months and greater	89,792	3,935
Total Fair Value	238,064	154,932
Amortized Cost
Amortized cost, less than 12 months	165,163	153,235
12 months and greater	108,802	4,036
Total Cost or Amortized Cost	273,965	157,271
Unrealized Loss
Less than 12 months	(16,891)	(2,238)
12 months and greater	(19,010)	(101)
Total Unrealized Loss	(35,901)	(2,339)
Corporate Debt
Fair value
Less than 12 months	773,433	217,791
12 months and greater	184,317	53,818
Total Fair Value	957,750	271,609
Amortized Cost
Amortized cost, less than 12 months	844,169	221,010
12 months and greater	216,914	55,704
Total Cost or Amortized Cost	1,061,083	276,714
Unrealized Loss
Less than 12 months	(70,736)	(3,219)
12 months and greater	(32,597)	(1,886)
Total Unrealized Loss	(103,333)	(5,105)
Municipal
Fair value
Less than 12 months	418,864	162,998
12 months and greater	76,783	15,037
Total Fair Value	495,647	178,035
Amortized Cost
Amortized cost, less than 12 months	493,485	166,602
12 months and greater	108,879	15,714
Total Cost or Amortized Cost	602,364	182,316
Unrealized Loss
Less than 12 months	(74,621)	(3,604)
12 months and greater	(32,096)	(677)
Total Unrealized Loss	$ (106,717)	$ (4,281)