Investments - Additional Information (Detail) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2025 USD ($) Security	Sep. 30, 2024 USD ($)	Sep. 30, 2025 USD ($) Security	Sep. 30, 2024 USD ($)	Jun. 30, 2025 USD ($)	Dec. 31, 2024 USD ($)
Marketable Securities [Line Items]
Individual fixed maturity held in unrealized loss position | Security	152		152
Number of fixed maturity securities, allowance for credit loss | Security	277		277
Fixed maturity securities, held-to-maturity, allowance for credit losses	$ 80		$ 80		$ 88	$ 116
Fixed maturity securities, available-for-sale, allowance for credit losses	0		0			0
Net realized gains (losses) on investments		$ 158	3,118	$ (181)
Net unrealized gains (losses) on equity securities	4,117	$ 3,873	2,794	$ 8,591
Corporate Bonds [Member]
Marketable Securities [Line Items]
Fixed maturity securities, held-to-maturity, allowance for credit losses	$ 56		$ 56		61	86
Number of majority securities | Security	11		11
States and Political Subdivisions [Member]
Marketable Securities [Line Items]
Fixed maturity securities, held-to-maturity, allowance for credit losses	$ 24		$ 24		$ 27	$ 30
Number of majority securities | Security	265		265
Corporate Fixed Income Securities [Member] | Maximum [Member]
Marketable Securities [Line Items]
Investments maturity period using default rate			20 years