Deferred Policy Acquisition Costs - Schedule of Major Categories of the Deferred Policy Acquisition Costs (Detail) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Deferred Charges Insurers [Abstract]
Agents’ commissions	$ 15,238	$ 15,286
Premium taxes	3,395	2,578
Deferred underwriting expenses	1,618	1,436
Total deferred policy acquisition costs	$ 20,251	$ 19,300	$ 20,412	$ 19,649