Investments - Additional Information (Detail)	3 Months Ended		6 Months Ended
	Jun. 30, 2019 USD ($) Security	Jun. 30, 2018 USD ($)	Jun. 30, 2019 USD ($) Security	Jun. 30, 2018 USD ($)
Investments Schedule [Abstract]
Individual fixed maturity held in unrealized loss position | Security	66		66
Individual fixed maturity held in unrealized loss position longer than 12 months | Security	61		61
Net unrealized gains (losses) on equity securities	$ 642,000	$ 76,000	$ 2,800,000	$ (314,000)
Impairment losses recognized	0	0	$ 0	0
Net realized losses from call of fixed maturity securities	$ 100,000
Net realized losses on sale of fixed maturity securities classified as available-for-sale		$ 1,100,000		$ 1,100,000