Investments - Additional Information (Detail) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2021 USD ($) Security	Jun. 30, 2020 USD ($)	Jun. 30, 2021 USD ($) Security	Jun. 30, 2020 USD ($)	Dec. 31, 2020 USD ($)
Marketable Securities [Line Items]
Individual fixed maturity held in unrealized loss position | Security	16		16
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	389		389
Fixed maturity securities, allowance for credit loss	$ 157		$ 157		$ 274
Available-for-sale, Allowance for Credit Losses	0		0		0
Net realized gains (losses)	1,200	$ 200	1,500	$ 1,200
Net unrealized gains (losses) on equity securities	3,286	$ 5,570	8,797	$ (3,193)
Corporate Bonds [Member]
Marketable Securities [Line Items]
Fixed maturity securities, allowance for credit loss	$ 111		$ 111		225
Number of majority securities | Security	21		21
States and Political Subdivisions [Member]
Marketable Securities [Line Items]
Fixed maturity securities, allowance for credit loss	$ 41		$ 41		$ 42
Number of majority securities | Security	365		365
Corporate Fixed Income Securities [Member] | Maximum [Member]
Marketable Securities [Line Items]
Investments maturity period using default rate			20 years