Net Loss Per Share - Basic and Diluted (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Numerator:
Net loss	$ (43,435)	$ (22,965)	$ (83,898)	$ (40,022)
Loss attributable to common stockholders - basic and diluted	$ (43,435)	$ (22,965)	$ (83,898)	$ (40,022)
Denominator:
Weighted-average number of common shares used in loss per share - basic and diluted (in shares)	43,042,883	37,895,651	43,027,903	37,089,642
Loss per share - basic and diluted (in dollars per share)	$ (1.01)	$ (0.61)	$ (1.95)	$ (1.08)