Reinsurance - Ceded Premiums Earned and Reinsurance Recoveries on Losses and Loss Adjustment Expenses (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Insurance [Abstract]
Ceded premiums earned	$ 425	$ 450	$ 372
Reinsurance recoveries on losses and loss adjustment expenses	$ 208	$ 589	$ 239