Nature of the Business and Basis of Presentation - Going Concern(Details) - USD ($) $ in Thousands	1 Months Ended	3 Months Ended
	May 31, 2017	Mar. 31, 2017	Mar. 31, 2016	Dec. 31, 2016	Dec. 31, 2015
Going Concern
Net losses		$ 22,753	$ 2,951
Accumulated deficit		94,209		$ 75,456
Cash		$ 52,286	$ 2,895	$ 23,565	$ 1,460
Net proceeds from issuance of shares, after deducting underwriting discounts and commissions and other offering expenses	$ 176,367