Stock Based Compensation, Share-Based Compensation (Details) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended
Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Stock-Based Compensation Expense [Abstract]
Stock-based compensation expense	$ 2,694	$ 2,612	$ 10,012	$ 10,780
Unrecognized share-based compensation cost	20,900		$ 20,900
Weighted average period expected to recognize unrecognized share-based compensation cost			1 year 9 months 14 days
Research and Development [Member]
Stock-Based Compensation Expense [Abstract]
Stock-based compensation expense	893	2,223	$ 4,711	5,075
General and Administrative [Member]
Stock-Based Compensation Expense [Abstract]
Stock-based compensation expense	$ 1,801	$ 389	$ 5,301	$ 5,705

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

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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Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
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Amount of cost not yet recognized for nonvested award under share-based payment arrangement.

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