Investments - Amortized Cost and Fair Values of Debt Securities (Details) - USD ($) $ in Thousands	Jun. 30, 2025	Dec. 31, 2024
Amortized cost
Due in one year or less	$ 743,265
Due after one year through five years	1,706,123
Due after five years through ten years	1,674,894
Due after ten years	966,783
Total debt securities with single maturity date, amortized cost	5,091,065
Amortized Cost	6,027,249	$ 6,178,123
Fair Value
Due in one year or less	741,517
Due after one year through five years	1,681,471
Due after five years through ten years	1,607,833
Due after ten years	851,298
Total debt securities with single maturity date, fair value	4,882,119
Total at end of period	5,802,331	5,851,689
ABS
Amortized cost
Total debt securities without single maturity date, amortized cost	183,698
Amortized Cost	183,698	155,594
Fair Value
Total debt securities without single maturity date, fair value	186,155
Total at end of period	186,155	156,517
RMBS
Amortized cost
Total debt securities without single maturity date, amortized cost	379,179
Amortized Cost	379,179	373,485
Fair Value
Total debt securities without single maturity date, fair value	363,279
Total at end of period	363,279	350,060
CMBS
Amortized cost
Total debt securities without single maturity date, amortized cost	248,872
Amortized Cost	248,872	243,840
Fair Value
Total debt securities without single maturity date, fair value	246,100
Total at end of period	246,100	235,871
CLOs
Amortized cost
Total debt securities without single maturity date, amortized cost	124,435
Amortized Cost	124,435	199,773
Fair Value
Total debt securities without single maturity date, fair value	124,678
Total at end of period	$ 124,678	$ 200,059