Selected Quarterly Financial Data (Unaudited) - Explanatory Information (Details) - $ / shares			1 Months Ended		12 Months Ended
	Nov. 08, 2018	Feb. 17, 2017	Jun. 30, 2017	Feb. 28, 2017	Dec. 31, 2018	Dec. 31, 2017
Cowen Sales Agreement
Selected Quarterly Financial Data (Unaudited)
Issuance of common stock, net of issuance costs (in shares)					651,525
Public offering price (in dollars per share)					$ 6.25
Common Stock
Selected Quarterly Financial Data (Unaudited)
Issuance of common stock, net of issuance costs (in shares)					20,651,524	12,019,639
Common Stock | Over-allotment option
Selected Quarterly Financial Data (Unaudited)
Issuance of common stock, net of issuance costs (in shares)	2,608,695	750,000
Common Stock | Underwritten Public Offering
Selected Quarterly Financial Data (Unaudited)
Issuance of common stock, net of issuance costs (in shares)	19,999,999		4,800,000	5,750,000
Public offering price (in dollars per share)	$ 2.30		$ 6.25	$ 5.00