Income Taxes - Components of Provision for (Benefit from) Income Taxes (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Current tax provision (benefit):
Federal	$ 0	$ 0	$ 0
State	0	0	0
Foreign	(180)	183	170
Total current tax provision (benefit)	(180)	183	170
Deferred tax provision (benefit):
Foreign	(122)	(27)	(27)
Total deferred tax provision (benefit)	(122)	(27)	(27)
Total provision for (benefit from) income taxes	$ (302)	$ 156	$ 143