Investments - Amortized Cost and Estimated Fair Value, Net of Credit Loss Allowance, of Fixed Maturity Securities by Contractual Maturity (Details) - USD ($) $ in Thousands	Mar. 31, 2025	Dec. 31, 2024
Available-for-sale securities, Amortized cost
Due in one year or less	$ 53,577
Due after one year through five years	479,358
Due after five years through ten years	187,422
Due after ten years	407,384
Amortized cost	1,127,741
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	52,860
Due after one year through five years	479,252
Due after five years through ten years	187,375
Due after ten years	393,220
Estimated fair value	1,112,707
Held-to-maturity securities, Estimated fair value
Held-to-maturity securities - due after ten years	4,902
Amortized cost	1,132,574	$ 1,070,789
Estimated fair value	1,117,609	$ 1,048,549
Fair value of securities lent	$ 12,300