Income Taxes - Provision for Income Taxes (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Current
Federal	$ 0	$ 0	$ 0
State	56	62	34
Foreign	2,139	1,654	857
Total current provision	2,195	1,716	891
Deferred
Federal	4	130	63
State	13	6	(1)
Foreign	(1,751)	(680)	(271)
Total deferred provision	(1,734)	(544)	(209)
Provision for income taxes	$ 461	$ 1,172	$ 682