Investments - Amortized Cost and Fair Values of Debt Securities (Details) - USD ($) $ in Thousands	Mar. 31, 2025	Dec. 31, 2024
Amortized cost
Due in one year or less	$ 742,080
Due after one year through five years	1,664,014
Due after five years through ten years	1,809,299
Due after ten years	964,380
Total debt securities with single maturity date, amortized cost	5,179,773
Amortized Cost	6,146,055	$ 6,178,123
Fair Value
Due in one year or less	740,345
Due after one year through five years	1,634,666
Due after five years through ten years	1,717,716
Due after ten years	846,400
Total debt securities with single maturity date, fair value	4,939,127
Total at end of period	5,885,033	5,851,689
ABS
Amortized cost
Total debt securities without single maturity date, amortized cost	180,604
Amortized Cost	180,604	155,594
Fair Value
Total debt securities without single maturity date, fair value	182,391
Total at end of period	182,391	156,517
RMBS
Amortized cost
Total debt securities without single maturity date, amortized cost	375,046
Amortized Cost	375,046	373,485
Fair Value
Total debt securities without single maturity date, fair value	357,989
Total at end of period	357,989	350,060
CMBS
Amortized cost
Total debt securities without single maturity date, amortized cost	264,095
Amortized Cost	264,095	243,840
Fair Value
Total debt securities without single maturity date, fair value	258,945
Total at end of period	258,945	235,871
CLOs
Amortized cost
Total debt securities without single maturity date, amortized cost	146,537
Amortized Cost	146,537	199,773
Fair Value
Total debt securities without single maturity date, fair value	146,581
Total at end of period	$ 146,581	$ 200,059