Income Taxes - Provisions/ Benefit (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Income Tax Disclosure [Abstract]
Federal									$ 0	$ 0	$ 0
State									191	25	42
Foreign									1,407	621	702
Total current									1,598	646	744
Federal									0	0	0
State									0	0	0
Foreign									(61)	(10)	(15)
Total deferred									(61)	(10)	(15)
Provision for income taxes	$ 1,079	$ (3)	$ 128	$ 333	$ (120)	$ 314	$ 228	$ 214	$ 1,537	$ 636	$ 729