Stock-Based Compensation - Summary of Stock-Based Compensation Expense (Details) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended
Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Share-based compensation expense
Stock-based compensation expense	$ 722	$ 672	$ 2,064	$ 1,511
Unrecognized stock-based compensation expense	5,500		$ 5,500
Unrecognized compensation expense, weighted-average period expected to be recognized			2 years 9 months 18 days
Research and Development
Share-based compensation expense
Stock-based compensation expense	132	122	$ 378	367
General and Administrative
Share-based compensation expense
Stock-based compensation expense	504	499	1,403	938
Sales and Marketing
Share-based compensation expense
Stock-based compensation expense	$ 86	$ 51	$ 283	$ 206

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

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-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.

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