Nature of Business (Details) - USD ($) $ / shares in Units, $ in Thousands	1 Months Ended	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2018	Dec. 31, 2017
Nature of Business
Accumulated deficit		$ 316,701	$ 298,049
Public offering of common stock, net of issuance costs (in shares)		3,126,998
Offering price (in dollars per share)		$ 11.36
Sale of Stock, Consideration Received if Additional Shares are Issued	$ 60,000
Commission fee percentage on gross proceeds from sale of ATM shares	3.00%
Proceeds from the offering, after deducting underwriting discounts and commissions		$ 34,283