Stock-Based Compensation - Summary 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
Stock-based compensation expense	$ 895	$ 722	$ 2,397	$ 2,064
Unrecognized stock-based compensation expense	5,100		$ 5,100
Unrecognized compensation expense, weighted-average period expected to be recognized			2 years 6 months
Research and development
Share-based compensation expense
Stock-based compensation expense	176	132	$ 484	378
General and administrative
Share-based compensation expense
Stock-based compensation expense	627	504	1,692	1,403
Sales and marketing
Share-based compensation expense
Stock-based compensation expense	$ 92	$ 86	$ 221	$ 283

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

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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