Investments - Amortized Cost and Fair Values of Debt Securities (Details) - USD ($) $ in Thousands	Jun. 30, 2024	Dec. 31, 2023
Amortized cost
Due in one year or less	$ 724,100
Due after one year through five years	1,549,563
Due after five years through ten years	1,797,579
Due after ten years	956,157
Total debt securities with single maturity date, amortized cost	5,027,399
Amortized Cost	6,150,471
Fair Value
Due in one year or less	718,932
Due after one year through five years	1,498,402
Due after five years through ten years	1,670,721
Due after ten years	815,170
Total debt securities with single maturity date, fair value	4,703,225
Total at end of period	5,789,968
ABS
Amortized cost
Total debt securities without single maturity date, amortized cost	174,794
Amortized Cost	174,794	$ 173,256
Fair Value
Total debt securities without single maturity date, fair value	173,872
Total at end of period	173,872	171,273
RMBS
Amortized cost
Total debt securities without single maturity date, amortized cost	381,258
Amortized Cost	381,258	347,132
Fair Value
Total debt securities without single maturity date, fair value	358,317
Total at end of period	358,317	330,773
CMBS
Amortized cost
Total debt securities without single maturity date, amortized cost	275,559
Amortized Cost	275,559	293,204
Fair Value
Total debt securities without single maturity date, fair value	262,826
Total at end of period	262,826	277,457
CLOs
Amortized cost
Total debt securities without single maturity date, amortized cost	291,461
Amortized Cost	291,461	327,467
Fair Value
Total debt securities without single maturity date, fair value	291,728
Total at end of period	$ 291,728	$ 326,096