Stockholders' Equity - Common stock (Details) $ in Thousands	3 Months Ended
	Mar. 31, 2020 Vote shares	Mar. 31, 2019 USD ($)	Dec. 31, 2019 shares
Common stock
Net proceeds from offering of common stock | $		$ 92,162
Number of shares reserved for future issuance	6,848,955		7,782,582
Stock options.
Common stock
Number of shares reserved for future issuance	6,049,288		4,720,772
Restricted stock units
Common stock
Number of shares reserved for future issuance	760,193		447,336
Warrants
Common stock
Number of shares reserved for future issuance	39,474		39,474
Exchange warrants
Common stock
Number of shares reserved for future issuance			2,575,000
Common Stock
Common stock
Number of votes for each shares held | Vote	1
Warrants and share-based payment awards
Common stock
Number of shares reserved for future issuance	6,848,955		7,782,582