Stock-Based Compensation - Summary of Stock-Based Compensation Expense (Details) - USD ($) $ in Thousands	3 Months Ended
Mar. 31, 2019	Mar. 31, 2018
Share-based compensation expense
Stock-based compensation expense	$ 704	$ 625
Unrecognized stock-based compensation expense	$ 5,800
Unrecognized compensation expense, weighted-average period expected to be recognized	2 years 10 months 24 days
Research and development
Share-based compensation expense
Stock-based compensation expense	$ 147	108
General and administrative
Share-based compensation expense
Stock-based compensation expense	509	433
Sales and marketing
Share-based compensation expense
Stock-based compensation expense	$ 48	$ 84

Represents the expense recognized during the period arising from equity-based compensation arrangements (for example, shares of stock, unit, stock options or other equity instruments) with employees, directors and certain consultants qualifying for treatment as employees.

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

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

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- Definition

Weighted average period over which unrecognized compensation is expected to be recognized for equity-based compensation plans, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

+ References

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-Publisher FASB
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-Topic 718
-SubTopic 10
-Section 50
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- Definition

Unrecognized cost of unvested share-based awards, other than options, awarded to employees as compensation.

+ References

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