Investments - Additional Information (Detail)	3 Months Ended		9 Months Ended
	Sep. 30, 2017 USD ($) Security	Sep. 30, 2016 USD ($)	Sep. 30, 2017 USD ($) Security	Sep. 30, 2016 USD ($)	Dec. 31, 2016 USD ($)
Investments Schedule [Abstract]
Individual fixed maturity held in unrealized loss position | Security	169		169
Individual fixed maturity held in unrealized loss position longer than 12 months | Security	48		48
Carrying value of investments	$ 1,280,000		$ 1,280,000		$ 13,330,000
Impairment losses recognized			0	$ 0
Net realized gains (losses) on investments	$ (192,000)	$ 181,000	$ (761,000)	$ 974,000