Stock-Based Compensation - Distribution of Stock-Based Compensation Expense (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Share Based Compensation Expense [Line Items]
Stock-based compensation	$ 337	$ 551	$ 1,021	$ 1,014
Cost of Revenue
Share Based Compensation Expense [Line Items]
Stock-based compensation	29	28	83	46
Research and Development
Share Based Compensation Expense [Line Items]
Stock-based compensation	124	111	370	231
Selling, General and Administrative
Share Based Compensation Expense [Line Items]
Stock-based compensation	$ 184	$ 412	$ 568	$ 737