Investments - Additional Information (Detail) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021 USD ($) Security	Sep. 30, 2020 USD ($)	Sep. 30, 2021 USD ($) Security	Sep. 30, 2020 USD ($)	Jun. 30, 2021 USD ($)	Dec. 31, 2020 USD ($)
Marketable Securities [Line Items]
Individual fixed maturity held in unrealized loss position | Security	22		22
Individual fixed maturity held in unrealized loss position longer than 12 months | Security	0		0
Number of fixed maturity securities, allowance for credit loss | Security	378		378
Fixed maturity securities, allowance for credit loss	$ 172		$ 172		$ 157	$ 274
Available-for-sale, Allowance for Credit Losses	0		0			0
Net realized gains (losses)		$ 300	1,500	$ 1,500
Net unrealized gains (losses) on equity securities	(771)	$ 844	8,026	$ (2,349)
Corporate Bonds [Member]
Marketable Securities [Line Items]
Fixed maturity securities, allowance for credit loss	$ 123		$ 123		111	225
Number of majority securities | Security	20		20
States and Political Subdivisions [Member]
Marketable Securities [Line Items]
Fixed maturity securities, allowance for credit loss	$ 45		$ 45		$ 41	$ 42
Number of majority securities | Security	355		355
Corporate Fixed Income Securities [Member] | Maximum [Member]
Marketable Securities [Line Items]
Investments maturity period using default rate			20 years