Investments - Schedule of Fixed Income Securities by Contractual Maturity (Details) - USD ($) $ in Thousands	Jun. 30, 2024	Dec. 31, 2023
AFS, Fair Value
Due in one year or less fair value, AFS	$ 587,352
Due after one year through five years fair value, AFS	3,507,774
Due after five years through 10 years fair value, AFS	2,827,999
Due after 10 years fair value, AFS	745,908
Total AFS fixed income securities, Fair Value	7,669,033	$ 7,499,197
HTM, Carrying Value
Due in one year or less carrying value, HTM	820
Due after one year through five years carrying value, HTM	14,209
Due after five years through 10 years carrying value, HTM	4,467
Due after 10 years carrying value, HTM	0
Fixed income securities, held-to-maturity, net of allowance for credit losses	19,496	22,700
HTM, Fair Value
Due in one year or less fair value, HTM	810
Due after one year through five years fair value, HTM	13,662
Due after five years through 10 years fair value, HTM	4,084
Due after 10 years fair value, HTM	0
Total HTM fixed income securities, Fair Value	$ 18,556	$ 21,923