Income Taxes - Components of Income Tax Provision (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Current income tax provision:
Federal									$ 0	$ 0	$ 0
State									114	105	147
Foreign									1,580	1,838	1,139
Total current income tax provision									1,694	1,943	1,286
Deferred income tax benefit:
Federal									0	0	0
State									0	0	0
Foreign									52	(736)	(105)
Total deferred income tax benefit									52	(736)	(105)
Total income tax provision (benefit)	$ 308	$ 503	$ 364	$ 571	$ 313	$ 218	$ 141	$ 535	$ 1,746	$ 1,207	$ 1,181