Net Loss Per Share - Basic and Diluted (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Numerator:
Net loss	$ (56,939)	$ (40,463)
Loss attributable to common stockholders - basic and diluted	$ (56,939)	$ (40,463)
Denominator:
Weighted-average number of common shares used in loss per share - basic and diluted (in shares)	43,185,952	43,012,924
Loss per share - basic and diluted (in dollars per share)	$ (1.32)	$ (0.94)