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	Jun. 30, 2021	Dec. 31, 2020
U.S. government
Fair Value
Less than 12 months	$ 5,165	$ 5,680
Total Fair Value	5,165	5,680
Amortized Cost
Amortized cost, less than 12 months	5,938	5,937
Total Cost or Amortized Cost	5,938	5,937
Unrealized Loss
Less than 12 months	(773)	(257)
Total Unrealized Loss	(773)	(257)
Non-U.S. government & agency
Fair Value
Less than 12 months	2,878
Total Fair Value	2,878
Amortized Cost
Amortized cost, less than 12 months	3,000
Total Cost or Amortized Cost	3,000
Unrealized Loss
Less than 12 months	(122)
Total Unrealized Loss	(122)
Agency MBS
Fair Value
Less than 12 months	86,938	43,999
12 months and greater	21,686
Total Fair Value	108,624	43,999
Amortized Cost
Amortized cost, less than 12 months	88,540	44,732
12 months and greater	22,527
Total Cost or Amortized Cost	111,067	44,732
Unrealized Loss
Less than 12 months	(1,602)	(733)
12 months and greater	(841)
Total Unrealized Loss	(2,443)	(733)
ABS/CMBS/MBS
Fair Value
Less than 12 months	53,265	32,771
12 months and greater	2,392	16,161
Total Fair Value	55,657	48,932
Amortized Cost
Amortized cost, less than 12 months	53,838	33,094
12 months and greater	2,403	16,251
Total Cost or Amortized Cost	56,241	49,345
Unrealized Loss
Less than 12 months	(573)	(323)
12 months and greater	(11)	(90)
Total Unrealized Loss	(584)	(413)
Corporate Debt
Fair Value
Less than 12 months	134,859	52,655
12 months and greater	15,054	6,235
Total Fair Value	149,913	58,890
Amortized Cost
Amortized cost, less than 12 months	137,006	53,440
12 months and greater	15,152	6,383
Total Cost or Amortized Cost	152,158	59,823
Unrealized Loss
Less than 12 months	(2,147)	(785)
12 months and greater	(98)	(148)
Total Unrealized Loss	(2,245)	(933)
Municipal
Fair Value
Less than 12 months	85,153	25,676
12 months and greater	1,964
Total Fair Value	87,117	25,676
Amortized Cost
Amortized cost, less than 12 months	86,668	25,894
12 months and greater	2,054
Total Cost or Amortized Cost	88,722	25,894
Unrealized Loss
Less than 12 months	(1,515)	(218)
12 months and greater	(90)
Total Unrealized Loss	(1,605)	(218)
Debt Securities
Fair Value
Less than 12 months	368,258	160,781
12 months and greater	41,096	22,396
Total Fair Value	409,354	183,177
Amortized Cost
Amortized cost, less than 12 months	374,990	163,097
12 months and greater	42,136	22,634
Total Cost or Amortized Cost	417,126	185,731
Unrealized Loss
Less than 12 months	(6,732)	(2,316)
12 months and greater	(1,040)	(238)
Total Unrealized Loss	$ (7,772)	$ (2,554)