Investments - Schedule of Fixed Income Securities by Contractual Maturity (Details) - USD ($) $ in Thousands	Sep. 30, 2026	Dec. 31, 2025
AFS, Fair Value
Due in one year or less fair value, AFS	$ 432,032
Due after one year through five years fair value, AFS	3,420,422
Due after five years through ten years fair value, AFS	3,876,752
Due after ten years fair value, AFS	2,080,852
Total AFS fixed income securities, Fair Value	9,810,058	$ 9,457,176
HTM, Carrying Value
Due in one year or less carrying value, HTM	0
Due after one year through five years carrying value, HTM	19,705
Due after five years through ten years carrying value, HTM	2,200
Due after ten years carrying value, HTM	0
Fixed income securities, held-to-maturity, net of allowance for credit losses	21,905	23,942
HTM, Fair Value
Due in one year or less fair value, HTM	0
Due after one year through five years fair value, HTM	18,807
Due after five years through ten years fair value, HTM	2,177
Due after ten years fair value, HTM	0
Total HTM fixed income securities, Fair Value	$ 20,984	$ 23,939

Fair value of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), with single maturity date and allocated without single maturity date, maturing in sixth through tenth fiscal year following current fiscal year. Excludes interim and annual periods when interim periods are reported from current statement of financial position date (rolling approach).

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- Definition

Fair value of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), with single maturity date and allocated without single maturity date, maturing in second through fifth fiscal year following current fiscal year. Excludes interim and annual periods when interim periods are reported from current statement of financial position date (rolling approach).