Investments - Amortized Cost and Estimated Fair Value, Net of Credit Loss Allowance, of Fixed Maturity Securities by Contractual Maturity (Details) $ in Thousands	Mar. 31, 2024 USD ($)
Available-for-sale securities, Amortized cost
Due in one year or less	$ 72,252
Due after one year through five years	418,035
Due after five years through ten years	194,162
Due after ten years	317,457
Amortized cost	1,001,906
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	71,072
Due after one year through five years	408,886
Due after five years through ten years	192,549
Due after ten years	297,138
Estimated fair value	969,645
Held-to-maturity securities, Estimated fair value
Held-to-maturity securities - due after ten years	4,833
Amortized cost	1,006,739
Estimated fair value	$ 974,478