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Stock-Based Awards - Compensation (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Stock-based compensation expense
Stock-based compensation expense	$ 3,309	$ 4,598	$ 6,762	$ 8,870
Unrecognized stock-based compensation cost, options	8,195		8,195
Unrecognized compensation, RSUs	8,604		8,604
Cost of revenue.
Stock-based compensation expense
Stock-based compensation expense	252	223	512	429
Research and development
Stock-based compensation expense
Stock-based compensation expense	939	1,721	1,755	3,315
General and administrative
Stock-based compensation expense
Stock-based compensation expense	$ 2,118	$ 2,654	$ 4,495	$ 5,126
Options to purchase common stock
Stock-based compensation expense
Weighted average recognition period unrecognized stock-based compensation cost (in years)			1 year 6 months 7 days
Restricted stock unit awards
Stock-based compensation expense
Weighted average recognition period unrecognized stock-based compensation cost (in years)			2 years 1 month 17 days