Insurance Activity - Summary of Losses and Loss Adjustment Reserve Activity (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Liability For Unpaid Claims And Claims Adjustment Expense Net [Abstract]
Balance at beginning of period	$ 811	$ 5,063
Incurred (released) - prior periods	19	(669)
Paid or terminated - prior periods	(356)	(3,583)
Total losses and loss adjustment reserves	$ 474	$ 811