Represents the percentage of discount on share price treated as 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.

No definition available.

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- Definition

Amount of noncash expense for share-based payment arrangement.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 28
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=118932676&loc=d3e3602-108585

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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

The weighted average grant-date fair value of options granted during the reporting period as calculated by applying the disclosed option pricing methodology.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (d)(1)
-URI http://asc.fasb.org/extlink&oid=116856206&loc=d3e5070-113901

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Stock-Based Compensation - Accounting for Stock-based Compensation (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Share-based Compensation Arrangement by Share-based Payment Award
Percentage of share-based compensation expense			15.00%
Weighted average grant date fair value of options granted during the period (per share)			$ 1.65	$ 7.15
Stock-based compensation	$ 963	$ 1,327	$ 2,868	$ 4,454
Research and development
Share-based Compensation Arrangement by Share-based Payment Award
Stock-based compensation	337	314	1,005	1,441
Research and development \| Employee Stock Purchase Plans
Share-based Compensation Arrangement by Share-based Payment Award
Stock-based compensation	9	11	27	62
Research and development \| Equity Incentive Plans
Share-based Compensation Arrangement by Share-based Payment Award
Stock-based compensation	328	303	978	1,379
General and administrative
Share-based Compensation Arrangement by Share-based Payment Award
Stock-based compensation	626	989	1,863	2,989
General and administrative \| Employee Stock Purchase Plans
Share-based Compensation Arrangement by Share-based Payment Award
Stock-based compensation	4	8	18	40
General and administrative \| Equity Incentive Plans
Share-based Compensation Arrangement by Share-based Payment Award
Stock-based compensation	$ 622	981	$ 1,845	2,949
Restructuring costs
Share-based Compensation Arrangement by Share-based Payment Award
Stock-based compensation		24		24
Restructuring costs \| Employee Stock Purchase Plans
Share-based Compensation Arrangement by Share-based Payment Award
Stock-based compensation		$ 24		$ 24