Investments - Amortized Cost and Estimated Fair Value, Net of Credit Loss Allowance, of Fixed Maturity Securities by Remaining Contractual Term to Maturity (Details) - USD ($) $ in Thousands	Jun. 30, 2026	Dec. 31, 2025
Available-for-sale securities:
Due in one year or less	$ 63,311
Due after one year through five years	546,224
Due after five years through ten years	188,795
Due after ten years	647,867
Amortized cost	1,446,197
Held-to-maturity securities, Amortized cost
Held-to-maturity securities - due after ten years	4,833
Available-for-sale securities, Estimated fair value
Due in one year or less	63,363
Due after one year through five years	545,677
Due after five years through ten years	187,998
Due after ten years	636,184
Estimated fair value	1,433,222
Held-to-maturity securities, Estimated fair value
Held-to-maturity securities - due after ten years	4,848
Amortized cost	1,451,030	$ 1,368,061
Estimated fair value	1,438,070	1,369,691
Fair value of securities lent	$ 69,900	$ 64,500