Investments - Additional Information (Detail)	3 Months Ended		9 Months Ended
	Sep. 30, 2019 USD ($) Security	Sep. 30, 2018 USD ($)	Sep. 30, 2019 USD ($) Security	Sep. 30, 2018 USD ($)
Investments Debt And Equity Securities [Abstract]
Individual fixed maturity held in unrealized loss position | Security	43		43
Individual fixed maturity held in unrealized loss position longer than 12 months | Security	21		21
Net unrealized gains (losses) on equity securities	$ 365,000	$ 573,000	$ 3,165,000	$ 259,000
Impairment losses recognized	$ 0	0	$ 0	0
Net realized losses on sale of equity and fixed maturity securities and called fixed maturity securities		$ 300,000		$ 1,500,000