Income Taxes - Current Provision (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Current provision:
Federal	$ 0	$ 0	$ 0
State	73	78	30
Foreign	3,692	2,225	1,772
Total current provision	3,765	2,303	1,802
Deferred provision (benefit):
Federal	(309)	(86)	35
State	(10)	(4)	2
Foreign	281	221	(97)
Total deferred provision	(38)	131	(60)
Total income tax provision	$ 3,727	$ 2,434	$ 1,742