Investments - Summary of Amortized Cost, Gross Unrealized Gains and Losses, and Estimated Fair Value of Available-for-Sale Securities (Detail) - USD ($) $ in Thousands	Dec. 31, 2023	Dec. 31, 2022
Schedule of Available-for-sale Securities [Line Items]
Fixed-maturity securities, Cost or Amortized Cost	$ 387,687	$ 494,197
Fixed-maturity securities, Gross Unrealized Gain	340	81
Fixed-maturity securities, Gross Unrealized Loss	(4,789)	(10,377)
Fixed-maturity securities, Estimated Fair Value	383,238	483,901
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	359,630	463,648
Fixed-maturity securities, Gross Unrealized Gain	224	59
Fixed-maturity securities, Gross Unrealized Loss	(3,800)	(9,105)
Fixed-maturity securities, Estimated Fair Value	356,054	454,602
Fixed-Maturity Securities [Member] | Corporate Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Fixed-maturity securities, Cost or Amortized Cost	27,563	28,378
Fixed-maturity securities, Gross Unrealized Gain	116	20
Fixed-maturity securities, Gross Unrealized Loss	(975)	(1,205)
Fixed-maturity securities, Estimated Fair Value	26,704	27,193
Fixed-Maturity Securities [Member] | State, Municipalities, and Political Subdivisions [Member]
Schedule of Available-for-sale Securities [Line Items]
Fixed-maturity securities, Cost or Amortized Cost		1,389
Fixed-maturity securities, Gross Unrealized Loss		(6)
Fixed-maturity securities, Estimated Fair Value		1,383
Fixed-Maturity Securities [Member] | Exchange-Traded Debt [Member]
Schedule of Available-for-sale Securities [Line Items]
Fixed-maturity securities, Cost or Amortized Cost	494	683
Fixed-maturity securities, Gross Unrealized Gain		2
Fixed-maturity securities, Gross Unrealized Loss	(14)	(52)
Fixed-maturity securities, Estimated Fair Value	$ 480	633
Fixed-Maturity Securities [Member] | Redeemable Preferred Stock [Member]
Schedule of Available-for-sale Securities [Line Items]
Fixed-maturity securities, Cost or Amortized Cost		99
Fixed-maturity securities, Gross Unrealized Loss		(9)
Fixed-maturity securities, Estimated Fair Value		$ 90