Investments - Amortized Cost and Estimated Fair Value, Net of Credit Loss Allowance, of Fixed Maturity Securities by Contractual Maturity (Details) - USD ($) $ in Thousands	Jun. 30, 2025	Dec. 31, 2024
Available-for-sale securities, Amortized cost
Due in one year or less	$ 57,341
Due after one year through five years	478,964
Due after five years through ten years	177,290
Due after ten years	419,663
Amortized cost	1,133,258
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	56,820
Due after one year through five years	482,703
Due after five years through ten years	178,639
Due after ten years	407,986
Estimated fair value	1,126,148
Held-to-maturity securities, Estimated fair value
Held-to-maturity securities - due after ten years	4,830
Amortized cost	1,138,091	$ 1,070,789
Estimated fair value	1,130,978	$ 1,048,549
Fair value of securities lent	$ 35,500