Stock-Based Compensation - Distribution of Stock-Based Compensation Expense (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Share Based Compensation Expense [Line Items]
Stock-based compensation	$ 193	$ 161	$ 463	$ 289
Cost of Revenue
Share Based Compensation Expense [Line Items]
Stock-based compensation	9	8	18	13
Research and Development
Share Based Compensation Expense [Line Items]
Stock-based compensation	33	46	120	77
Selling, General and Administrative
Share Based Compensation Expense [Line Items]
Stock-based compensation	$ 151	$ 107	$ 325	$ 199