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

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The estimated dividend rate (a percentage of the share price) to be paid (expected dividends) to holders of the underlying shares over the option's term.

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Number of shares authorized for issuance under share-based payment arrangement.

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Summary of Significant Accounting Policies - Share-Based Compensation (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Apr. 30, 2016
Share-Based Compensation
Expected dividend yield	0.00%
Share-based compensation expense	$ 9,180	$ 11,072	$ 18,171
Research and development
Share-Based Compensation
Share-based compensation expense	4,260	4,967	11,114
General and administrative
Share-Based Compensation
Share-based compensation expense	4,920	6,105	$ 7,057
ESPP
Share-Based Compensation
Share-based compensation expense	$ 100	$ 0
ESPP \| Maximum
Share-Based Compensation
Number of shares reserved for issuance under the Plan (in shares)				1,000,000