Investments - Amortized Cost and Fair Values of Debt Securities (Details) - USD ($) $ in Thousands	Dec. 31, 2024	Dec. 31, 2023
Amortized Cost
Due in one year or less	$ 729,851
Due after one year through five years	1,669,360
Due after five years through ten years	1,771,814
Due after ten years	1,034,406
Total debt securities with single maturity date	5,205,431
Fair Value
Due in one year or less	728,644
Due after one year through five years	1,631,156
Due after five years through ten years	1,656,007
Due after ten years	893,375
Total debt securities with single maturity date	4,909,182
Total at end of period	5,851,689	$ 5,723,113
Total fixed income securities
Amortized Cost
Amortized Cost	6,178,123	6,061,022
Fair Value
Total at end of period	5,851,689	5,723,113
ABS
Amortized Cost
Total debt securities without single maturity date, amortized cost	155,594
Amortized Cost	155,594	173,256
Fair Value
Total debt securities without single maturity date, fair value	156,517
Total at end of period	156,517	171,273
RMBS
Amortized Cost
Total debt securities without single maturity date, amortized cost	373,485
Amortized Cost	373,485	347,132
Fair Value
Total debt securities without single maturity date, fair value	350,060
Total at end of period	350,060	330,773
CMBS
Amortized Cost
Total debt securities without single maturity date, amortized cost	243,840
Amortized Cost	243,840	293,204
Fair Value
Total debt securities without single maturity date, fair value	235,871
Total at end of period	235,871	277,457
CLOs
Amortized Cost
Total debt securities without single maturity date, amortized cost	199,773
Amortized Cost	199,773	327,467
Fair Value
Total debt securities without single maturity date, fair value	200,059
Total at end of period	$ 200,059	$ 326,096