Stock-Based Compensation - Distribution of Stock-Based Compensation Expense (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Share Based Compensation Expense [Line Items]
Stock-based compensation	$ 348	$ 193	$ 684	$ 463
Cost of Revenue
Share Based Compensation Expense [Line Items]
Stock-based compensation	28	9	54	18
Research and Development
Share Based Compensation Expense [Line Items]
Stock-based compensation	123	33	246	120
Selling, General and Administrative
Share Based Compensation Expense [Line Items]
Stock-based compensation	$ 197	$ 151	$ 384	$ 325