Stock-Based Awards - Stock-Based Compensation (Details) - USD ($) $ in Thousands	3 Months Ended
Mar. 31, 2020	Mar. 31, 2019
Stock-based Compensation
Stock-based compensation expense	$ 1,665	$ 1,942
Unrecognized stock-based compensation cost	$ 14,103
Weighted average period of unrecognized stock-based compensation cost expected to be recognized	2 years 9 months 18 days
Unvested service-based stock options held by nonemployees	0
Research and Development Expense
Stock-based Compensation
Stock-based compensation expense	$ 375	620
Selling and Marketing Expense
Stock-based Compensation
Stock-based compensation expense	371	219
General and Administrative Expense
Stock-based Compensation
Stock-based compensation expense	$ 919	$ 1,103

Non-vested stock options outstanding held by non-employees.

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