Investments - Amortized Cost and Fair Values of Debt Securities (Details) - USD ($) $ in Thousands	Jun. 30, 2022	Dec. 31, 2021
Amortized cost
Due in one year or less	$ 299,593
Due after one year through five years	1,536,218
Due after five years through ten years	1,822,146
Due after ten years	1,461,814
Total debt securities with single maturity date, amortized cost	5,119,771
Amortized Cost	6,087,857	$ 6,397,658
Fair Value
Due in one year or less	297,963
Due after one year through five years	1,489,620
Due after five years through ten years	1,695,419
Due after ten years	1,309,979
Total debt securities with single maturity date, fair value	4,792,981
Total at end of period	5,712,820	6,587,581
ABS
Amortized cost
Total debt securities without single maturity date, amortized cost	108,064
Amortized Cost	108,064	150,888
Fair Value
Total debt securities without single maturity date, fair value	103,268
Total at end of period	103,268	150,710
RMBS
Amortized cost
Total debt securities without single maturity date, amortized cost	240,109
Amortized Cost	240,109	309,991
Fair Value
Total debt securities without single maturity date, fair value	222,549
Total at end of period	222,549	309,110
CMBS
Amortized cost
Total debt securities without single maturity date, amortized cost	282,090
Amortized Cost	282,090	315,330
Fair Value
Total debt securities without single maturity date, fair value	266,611
Total at end of period	266,611	319,130
CLOs
Amortized cost
Total debt securities without single maturity date, amortized cost	337,823
Amortized Cost	337,823	360,436
Fair Value
Total debt securities without single maturity date, fair value	327,411
Total at end of period	$ 327,411	$ 360,939