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, 2026	Dec. 31, 2025
Schedule of Available-for-sale Securities [Line Items]
Fixed-maturity securities, Cost or Amortized Cost	$ 920,973	$ 595,383
Allowance for Credit Loss	0	0
Fixed-maturity securities, Gross Unrealized Gains	697	3,322
Fixed-maturity securities, Gross Unrealized Losses	(6,824)	(1,376)
Fixed-maturity securities, Estimated Fair Value	914,846	597,329
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	653,256	332,284
Fixed-maturity securities, Gross Unrealized Gains	487	1,785
Fixed-maturity securities, Gross Unrealized Losses	(5,455)	(717)
Fixed-maturity securities, Estimated Fair Value	648,288	333,352
Fixed-Maturity Securities [Member] \| Corporate Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Fixed-maturity securities, Cost or Amortized Cost	242,120	241,843
Fixed-maturity securities, Gross Unrealized Gains	192	1,463
Fixed-maturity securities, Gross Unrealized Losses	(1,174)	(384)
Fixed-maturity securities, Estimated Fair Value	241,138	242,922
Fixed-Maturity Securities [Member] \| Commercial Mortgage Backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Fixed-maturity securities, Cost or Amortized Cost	25,597	21,256
Fixed-maturity securities, Gross Unrealized Gains	18	74
Fixed-maturity securities, Gross Unrealized Losses	(195)	(275)
Fixed-maturity securities, Estimated Fair Value	$ 25,420	$ 21,055

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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