Investments - Scheduled Contractual Maturities of Fixed-Maturity Securities (Detail) - USD ($) $ in Thousands	Jun. 30, 2024	Dec. 31, 2023
Investments, Debt and Equity Securities [Abstract]
Due in one year or less, Cost or Amortized Cost	$ 232,194	$ 234,992
Due after one year through five years, Cost or Amortized Cost	408,367	148,935
Due after five years through ten years, Cost or Amortized Cost	2,837	3,266
Due after ten years, Cost or Amortized Cost	494	494
Fixed-maturity securities, Cost or Amortized Cost	643,892	387,687
Due in one year or less, Estimated Fair Value	229,497	234,025
Due after one year through five years, Estimated Fair Value	407,792	145,758
Due after five years through ten years, Estimated Fair Value	2,480	2,974
Due after ten years, Estimated Fair Value	473	481
Estimated Fair Value Total	$ 640,242	$ 383,238