Equity Incentive Plan - Stock-based compensation expense (Details) - USD ($)	3 Months Ended
Mar. 31, 2020	Mar. 31, 2019
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Stock-based compensation expense	$ 2,482,000	$ 776,000
Income tax benefits for stock-based compensation	0
Stock-based compensation costs capitalized	0
Research and development
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Stock-based compensation expense	1,058,000	419,000
General and administrative
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Stock-based compensation expense	$ 1,424,000	$ 357,000

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

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