Income Taxes - Provision for (Benefit from) Income Taxes (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Current:
Federal	$ 0	$ 0	$ 0
State	3	2	3
Foreign	98	(19)	(38)
Total current provision for (benefit from) income taxes	101	(17)	(35)
Deferred:
Federal	0	1	(26)
State	0	0	0
Total deferred provision for (benefit from) income taxes	0	1	(26)
Total	$ 101	$ (16)	$ (61)