Investments - Amortized Cost and Fair Values of Debt Securities (Details) - USD ($) $ in Thousands	Jun. 30, 2023	Dec. 31, 2022
Amortized cost
Due in one year or less	$ 689,833
Due after one year through five years	1,544,694
Due after five years through ten years	1,697,804
Due after ten years	1,099,616
Total debt securities with single maturity date, amortized cost	5,031,947
Amortized Cost	6,056,298	$ 5,926,785
Fair Value
Due in one year or less	680,414
Due after one year through five years	1,465,881
Due after five years through ten years	1,550,754
Due after ten years	937,441
Total debt securities with single maturity date, fair value	4,634,490
Total at end of period	5,603,038	5,409,698
ABS
Amortized cost
Total debt securities without single maturity date, amortized cost	127,142
Amortized Cost	127,142	126,723
Fair Value
Total debt securities without single maturity date, fair value	121,954
Total at end of period	121,954	120,687
RMBS
Amortized cost
Total debt securities without single maturity date, amortized cost	260,147
Amortized Cost	260,147	223,743
Fair Value
Total debt securities without single maturity date, fair value	236,571
Total at end of period	236,571	198,009
CMBS
Amortized cost
Total debt securities without single maturity date, amortized cost	301,682
Amortized Cost	301,682	257,785
Fair Value
Total debt securities without single maturity date, fair value	279,572
Total at end of period	279,572	237,216
CLOs
Amortized cost
Total debt securities without single maturity date, amortized cost	335,380
Amortized Cost	335,380	337,656
Fair Value
Total debt securities without single maturity date, fair value	330,451
Total at end of period	$ 330,451	$ 329,832