Investments - Additional Information (Detail)	3 Months Ended
	Mar. 31, 2019 USD ($) Security	Mar. 31, 2018 USD ($)
Investments Schedule [Abstract]
Individual fixed maturity held in unrealized loss position | Security	184
Individual fixed maturity held in unrealized loss position longer than 12 months | Security	176
Net unrealized gains (losses) on equity securities	$ 2,200,000	$ (400,000)
Impairment losses recognized	0	0
Net realized gain on sale of equity and fixed maturity securities classified as available-for-sale	$ 59,000	$ (31,000)