Industry and Geographic Information - Narrative (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2017 USD ($) segment	Dec. 31, 2016 USD ($)	Dec. 31, 2015
Segment Reporting [Abstract]
Number of operating segments | segment	1
Concentration Risk [Line Items]
Balances due	$ 1,946	$ 34
Total revenue | One Customer
Concentration Risk [Line Items]
Risk concentration	18.00%
Total revenue | Geographic Concentration | Outside the U.S.
Concentration Risk [Line Items]
Risk concentration	28.00%	3.00%	0.00%
Balances due from Foreign Customers | Geographic Concentration | Outside the U.S.
Concentration Risk [Line Items]
Balances due	$ 1,000	$ 3