Investments - Amortized Cost and Fair Values of Debt Securities (Details) - USD ($) $ in Thousands	Sep. 30, 2025	Dec. 31, 2024
Amortized cost
Due in one year or less	$ 811,265
Due after one year through five years	1,732,277
Due after five years through ten years	1,617,864
Due after ten years	954,007
Total debt securities with single maturity date, amortized cost	5,115,413
Amortized Cost	6,036,944	$ 6,178,123
Fair Value
Due in one year or less	810,672
Due after one year through five years	1,708,964
Due after five years through ten years	1,572,906
Due after ten years	862,932
Total debt securities with single maturity date, fair value	4,955,474
Total at end of period	5,868,594	5,851,689
ABS
Amortized cost
Total debt securities without single maturity date, amortized cost	206,520
Amortized Cost	206,520	155,594
Fair Value
Total debt securities without single maturity date, fair value	208,666
Total at end of period	208,666	156,517
RMBS
Amortized cost
Total debt securities without single maturity date, amortized cost	372,361
Amortized Cost	372,361	373,485
Fair Value
Total debt securities without single maturity date, fair value	361,846
Total at end of period	361,846	350,060
CMBS
Amortized cost
Total debt securities without single maturity date, amortized cost	224,852
Amortized Cost	224,852	243,840
Fair Value
Total debt securities without single maturity date, fair value	224,622
Total at end of period	224,622	235,871
CLOs
Amortized cost
Total debt securities without single maturity date, amortized cost	117,798
Amortized Cost	117,798	199,773
Fair Value
Total debt securities without single maturity date, fair value	117,986
Total at end of period	$ 117,986	$ 200,059