Investments - Additional Information (Detail) $ in Thousands	3 Months Ended
	Mar. 31, 2024 USD ($) Security	Mar. 31, 2023 USD ($)	Dec. 31, 2023 USD ($)	Sep. 30, 2023 USD ($) Security
Marketable Securities [Line Items]
Individual fixed maturity held in unrealized loss position | Security	158
Number of fixed maturity securities, allowance for credit loss | Security				463
Fixed maturity securities, held-to-maturity, allowance for credit losses	$ 165		$ 182	$ 200
Available-for-sale, Allowance for Credit Losses	0		0
Net realized gains (losses) on investments	(222)	$ 258
Net unrealized gains on equity securities	4,776	$ 1,369
Corporate Bonds [Member]
Marketable Securities [Line Items]
Fixed maturity securities, held-to-maturity, allowance for credit losses	126		142
Number of majority securities | Security				19
States and Political Subdivisions [Member]
Marketable Securities [Line Items]
Fixed maturity securities, held-to-maturity, allowance for credit losses	$ 37		$ 38
Number of majority securities | Security				441
Corporate Fixed Income Securities [Member] | Maximum [Member]
Marketable Securities [Line Items]
Investments maturity period using default rate	20 years