Stock-Based Awards, Stock-Based Compensation (Details) - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Stock-Based Compensation [Abstract]
Share based compensation expense	$ 18,567	$ 13,371	$ 13,601
Expense in connection with warrant issue	26,562	0	0
Unrecognized share-based compensation cost	$ 30,400
Weighted average period expected to recognize unrecognized share-based compensation cost	2 years 1 month 6 days
Research and Development [Member]
Stock-Based Compensation [Abstract]
Share based compensation expense	$ 7,355	6,153	7,375
General and Administrative [Member]
Stock-Based Compensation [Abstract]
Share based compensation expense	11,211	7,218	6,226
Common Stock Warrant [Member]
Stock-Based Compensation [Abstract]
Expense in connection with warrant issue	26,600
Stock Options [Member]
Stock-Based Compensation [Abstract]
Share based compensation expense	18,527	13,371	13,601
Restricted Stock Units [Member]
Stock-Based Compensation [Abstract]
Share based compensation expense	40	$ 0	$ 0
Unrecognized share-based compensation cost	$ 500
Weighted average period expected to recognize unrecognized share-based compensation cost	2 years 9 months 18 days

Adjustment for noncash service expenses paid for by granting of warrants.

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

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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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