Stockholders' Equity - Common stock (Details) $ / shares in Units, $ in Thousands	1 Months Ended	3 Months Ended	9 Months Ended
	Mar. 31, 2019 USD ($) $ / shares shares	Mar. 31, 2019 $ / shares shares	Sep. 30, 2019 USD ($) Vote shares	Dec. 31, 2018 shares
Common stock
Net proceeds from public offering of common stock | $	$ 92,162		$ 92,162
Common stock
Common stock
Number of votes for each shares held | Vote			1
Issuance of common stock under public offering, net of issuance costs (in shares)	24,437,500	24,437,500
Share price (in dollars per share) | $ / shares	$ 4.00	$ 4.00
Warrants and share-based payment awards
Common stock
Number of shares reserved for future issuance			5,205,407	3,856,932
Warrants
Common stock
Number of shares reserved for future issuance			39,474	110,365
Share-based payments | Restricted stock units
Common stock
Number of shares reserved for future issuance			447,336
Share-based payments | Stock options.
Common stock
Number of shares reserved for future issuance			4,718,597	3,746,567