Income Taxes - Components of the (Benefit) Provision for Income Taxes (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Current:
Federal	$ (46)	$ 80	$ (9)
State	0	11	14
Foreign	0	0	0
Total current	(46)	91	5
Deferred:
Foreign	(140)	0	0
Total deferred	(140)	0	0
(Benefit) provision for income taxes	$ (186)	$ 91	$ 5