Net Loss per Share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Numerator:
Net loss	$ (37,565)	$ (30,229)
Denominator:
Weighted average shares of common stock outstanding (in shares)	41,248,663	30,885,928
Net loss per share, basic and diluted	$ (0.91)	$ (0.98)