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, 2021	Dec. 31, 2020
U.S. government
Fair value
Less than 12 months	$ 2,942	$ 5,680
Total Fair Value	2,942	5,680
Amortized Cost
Amortized cost, less than 12 months	2,986	5,937
Total Cost or Amortized Cost	2,986	5,937
Unrealized Loss
Less than 12 months	(44)	(257)
Total Unrealized Loss	(44)	(257)
U.S. Agency
Fair value
Less than 12 months	1,498
Total Fair Value	1,498
Amortized Cost
Amortized cost, less than 12 months	1,515
Total Cost or Amortized Cost	1,515
Unrealized Loss
Less than 12 months	(17)
Total Unrealized Loss	(17)
Non-U.S. govt. & agency
Fair value
Less than 12 months	4,346
Total Fair Value	4,346
Amortized Cost
Amortized cost, less than 12 months	4,500
Total Cost or Amortized Cost	4,500
Unrealized Loss
Less than 12 months	(154)
Total Unrealized Loss	(154)
Agency MBS
Fair value
Less than 12 months	102,145	43,999
12 months and greater	62,669
Total Fair Value	164,814	43,999
Amortized Cost
Amortized cost, less than 12 months	104,336	44,732
12 months and greater	65,429
Total Cost or Amortized Cost	169,765	44,732
Unrealized Loss
Less than 12 months	(2,191)	(733)
12 months and greater	(2,760)
Total Unrealized Loss	(4,951)	(733)
ABS/CMBS/MBS
Fair value
Less than 12 months	150,997	32,771
12 months and greater	3,935	16,161
Total Fair Value	154,932	48,932
Amortized Cost
Amortized cost, less than 12 months	153,235	33,094
12 months and greater	4,036	16,251
Total Cost or Amortized Cost	157,271	49,345
Unrealized Loss
Less than 12 months	(2,238)	(323)
12 months and greater	(101)	(90)
Total Unrealized Loss	(2,339)	(413)
Corporate Debt
Fair value
Less than 12 months	217,791	52,655
12 months and greater	53,818	6,235
Total Fair Value	271,609	58,890
Amortized Cost
Amortized cost, less than 12 months	221,010	53,440
12 months and greater	55,704	6,383
Total Cost or Amortized Cost	276,714	59,823
Unrealized Loss
Less than 12 months	(3,219)	(785)
12 months and greater	(1,886)	(148)
Total Unrealized Loss	(5,105)	(933)
Municipal
Fair value
Less than 12 months	162,998	25,676
12 months and greater	15,037
Total Fair Value	178,035	25,676
Amortized Cost
Amortized cost, less than 12 months	166,602	25,894
12 months and greater	15,714
Total Cost or Amortized Cost	182,316	25,894
Unrealized Loss
Less than 12 months	(3,604)	(218)
12 months and greater	(677)
Total Unrealized Loss	(4,281)	(218)
Debt Securities
Fair value
Less than 12 months	642,717	160,781
12 months and greater	135,459	22,396
Total Fair Value	778,176	183,177
Amortized Cost
Amortized cost, less than 12 months	654,184	163,097
12 months and greater	140,883	22,634
Total Cost or Amortized Cost	795,067	185,731
Unrealized Loss
Less than 12 months	(11,467)	(2,316)
12 months and greater	(5,424)	(238)
Total Unrealized Loss	$ (16,891)	$ (2,554)