Income Taxes - Summary of Income Tax Expense (Benefit) (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Current:
Federal		$ 0	$ 0
State	$ (1)	(153)	5
Foreign	40	61	63
Total current	39	(92)	68
Deferred:
Federal	(530)	0	0
State	0	0	0
Foreign	(55)	(137)	0
Total deferred	(585)	(137)	0
Total provision	$ (546)	$ (229)	$ 68