Investments - Summary of Amortized Cost, Allowance for Credit Loss, Gross Unrealized Gains and Losses, and Estimated Fair Value of Available-for-Sale Securities (Detail) - USD ($) $ in Thousands	Jun. 30, 2024	Dec. 31, 2023
Schedule of Available-for-sale Securities [Line Items]
Fixed-maturity securities, Cost or Amortized Cost	$ 643,892	$ 387,687
Allowance for Credit Loss	0	0
Fixed-maturity securities, Gross Unrealized Gain	319	340
Fixed-maturity securities, Gross Unrealized Loss	(3,969)	(4,789)
Fixed-maturity securities, Estimated Fair Value	640,242	383,238
Fixed-Maturity Securities [Member] | U.S. Treasury and U.S. Government Agencies [Member]
Schedule of Available-for-sale Securities [Line Items]
Fixed-maturity securities, Cost or Amortized Cost	612,692	359,630
Fixed-maturity securities, Gross Unrealized Gain	284	224
Fixed-maturity securities, Gross Unrealized Loss	(2,999)	(3,800)
Fixed-maturity securities, Estimated Fair Value	609,977	356,054
Fixed-Maturity Securities [Member] | Corporate Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Fixed-maturity securities, Cost or Amortized Cost	30,705	27,563
Fixed-maturity securities, Gross Unrealized Gain	35	116
Fixed-maturity securities, Gross Unrealized Loss	(948)	(975)
Fixed-maturity securities, Estimated Fair Value	29,792	26,704
Fixed-Maturity Securities [Member] | Exchange-Traded Debt [Member]
Schedule of Available-for-sale Securities [Line Items]
Fixed-maturity securities, Cost or Amortized Cost	495	494
Fixed-maturity securities, Gross Unrealized Gain	0
Fixed-maturity securities, Gross Unrealized Loss	(22)	(14)
Fixed-maturity securities, Estimated Fair Value	$ 473	$ 480