Investments - Additional Information (Detail)	12 Months Ended
	Dec. 31, 2016 USD ($) Security	Dec. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)
Investment [Line Items]
Short-term investments	$ 29,580,000	$ 7,718,000
Carrying value of investments	13,330,000	12,217,000
Sale of securities classified as held to maturity	3,000,000
Gain of held-to-maturity investment securities	$ 100,000
Individual fixed maturity held in unrealized loss position | Security	260
Individual fixed maturity held in unrealized loss position longer than 12 months | Security	17
Impairment losses recognized	$ 0	2,653,000	$ 222,000
Cash [Member]
Investment [Line Items]
Cash or cash held by insurance regulators	100,000
Held-to-Maturity Securities [Member]
Investment [Line Items]
Cash or cash held by insurance regulators	21,200,000
Available-for-Sale Securities [Member]
Investment [Line Items]
Cash or cash held by insurance regulators	400,000
Corporate Bonds [Member]
Investment [Line Items]
Short-term investments	2,800,000	$ 7,700,000
U.S. Treasury Securities and Obligations of U.S. Government Agencies [Member]
Investment [Line Items]
Short-term investments	21,900,000
States and Political Subdivisions [Member]
Investment [Line Items]
Short-term investments	$ 4,900,000