Net Loss per Share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Numerator:
Net loss attributable to common shareholders	$ (24,406)	$ (16,029)	$ (60,647)	$ (32,172)
Denominator:
Weighted average common shares outstanding — basic and diluted	48,183,424	1,942,106	23,174,841	1,675,133
Net loss per share attributable to common shareholders — basic and diluted	$ (0.51)	$ (8.25)	$ (2.62)	$ (19.21)