Net Loss Per Share - Calculation of Basic and Diluted Net Income (Loss) Per Share Attributable to Common Stockholders (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Numerator:
Net loss	$ (56,473)	$ (49,625)	$ (97,135)	$ (382,957)
Denominator:
Weighted-average shares outstanding—basic and diluted (in shares)	170,419,083	163,838,755	169,585,356	162,952,721
Net loss per share—basic and diluted:
Net loss per share, basic and diluted (in USD per share)	$ (0.33)	$ (0.30)	$ (0.57)	$ (2.35)