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, 2024	Dec. 31, 2023
Available-for-sale securities, Amortized cost
Due in one year or less	$ 47,471
Due after one year through five years	441,071
Due after five years through ten years	189,349
Due after ten years	352,802
Amortized cost	1,030,693
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	46,768
Due after one year through five years	433,520
Due after five years through ten years	188,453
Due after ten years	331,643
Estimated fair value	1,000,384
Held-to-maturity securities, Estimated fair value
Held-to-maturity securities - due after ten years	4,833
Amortized cost	1,035,526
Estimated fair value	1,005,217
Fair value of loaned securities	$ 6,125	$ 0