Investments - Additional Information (Detail)	3 Months Ended		6 Months Ended
	Jun. 30, 2020 USD ($) Security	Jun. 30, 2019 USD ($)	Jun. 30, 2020 USD ($) Security	Jun. 30, 2019 USD ($)	Dec. 31, 2019 USD ($)
Marketable Securities [Line Items]
Individual fixed maturity held in unrealized loss position | Security	2		2
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	390		390
Fixed maturity securities, allowance for credit loss	$ 357,000		$ 357,000		$ 0
Fixed maturity securities, available-for-sale, allowance for credit losses	0		0		$ 0
Net realized gains (losses)	200,000	$ (100,000)	1,200,000
Net unrealized gains (losses) on equity securities	5,570,000	$ 642,000	(3,193,000)	$ 2,800,000
Corporate Bonds [Member]
Marketable Securities [Line Items]
Fixed maturity securities, allowance for credit loss	$ 299,000		$ 299,000
Number of majority securities | Security	32		32
States and Political Subdivisions [Member]
Marketable Securities [Line Items]
Fixed maturity securities, allowance for credit loss	$ 49,000		$ 49,000
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