Stock-Based Awards - Stock-Based 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
Stock-based compensation expense	$ 1,826	$ 1,695	$ 3,491	$ 3,637
Unrecognized stock-based compensation cost	$ 13,121		$ 13,121
Weighted average period of unrecognized stock-based compensation cost expected to be recognized			2 years 6 months
Unvested service-based stock options held by nonemployees	12,000		12,000
Research and Development Expense
Stock-based Compensation
Stock-based compensation expense	$ 362	593	$ 737	1,213
Selling and Marketing Expense
Stock-based Compensation
Stock-based compensation expense	433	238	804	458
General and Administrative Expense
Stock-based Compensation
Stock-based compensation expense	$ 1,031	$ 864	$ 1,950	$ 1,966

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

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Amount of expense for award under share-based payment arrangement. Excludes amount capitalized.

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Amount of cost not yet recognized for nonvested award under share-based payment arrangement.

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