Stock-Based Awards - Stock-Based Compensation Expense (Details) - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Stock-based Compensation
Stock-based compensation expense	$ 8,759	$ 7,483	$ 7,321
Unrecognized stock-based compensation cost	$ 10,566
Weighted average period of unrecognized stock-based compensation cost expected to be recognized	2 years 6 months
Research and Development Expense
Stock-based Compensation
Stock-based compensation expense	$ 2,312	2,557	2,584
Selling and Marketing Expense
Stock-based Compensation
Stock-based compensation expense	1,013	449	633
General and Administrative Expense
Stock-based Compensation
Stock-based compensation expense	$ 5,434	$ 4,477	$ 4,104

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.

No definition available.

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

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
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Weighted-average period over which cost not yet recognized is expected to be recognized for award under share-based payment arrangement, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents reported fact of one year, five months, and thirteen days.

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Amount of noncash expense for share-based payment arrangement.

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