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	Mar. 31, 2025	Dec. 31, 2024
Schedule of Available-for-sale Securities [Line Items]
Fixed-maturity securities, Cost or Amortized Cost	$ 651,071	$ 719,536
Allowance for Credit Loss	0	0
Fixed-maturity securities, Gross Unrealized Gain	2,368	2,098
Fixed-maturity securities, Gross Unrealized Loss	(578)	(3,097)
Fixed-maturity securities, Estimated Fair Value	652,861	718,537
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	624,650	688,123
Fixed-maturity securities, Gross Unrealized Gain	2,229	2,019
Fixed-maturity securities, Gross Unrealized Loss	(306)	(2,726)
Fixed-maturity securities, Estimated Fair Value	626,573	687,416
Fixed-Maturity Securities [Member] \| Corporate Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Fixed-maturity securities, Cost or Amortized Cost	25,927	30,919
Fixed-maturity securities, Gross Unrealized Gain	139	77
Fixed-maturity securities, Gross Unrealized Loss	(242)	(371)
Fixed-maturity securities, Estimated Fair Value	25,824	30,625
Fixed-Maturity Securities [Member] \| Exchange-Traded Debt [Member]
Schedule of Available-for-sale Securities [Line Items]
Fixed-maturity securities, Cost or Amortized Cost	494	494
Fixed-maturity securities, Gross Unrealized Gain		2
Fixed-maturity securities, Gross Unrealized Loss	(30)
Fixed-maturity securities, Estimated Fair Value	$ 464	$ 496

Amount, before tax, of unrealized gain in accumulated other comprehensive income (AOCI) on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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