Net Loss Per Share - Summary of Basic and Diluted Net Loss Per Share (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Numerator:
Net loss	$ (16,978)	$ (70,202)	$ (91,576)	$ (126,979)
Denominator:
Weighted average common stock outstanding —basic	46,541,716	37,361,129	45,439,666	37,315,393
Dilutive effect of shares of common stock equivalents resulting from common stock options and restricted stock units	0	0	0	0
Weighted average common stock outstanding —diluted	46,541,716	37,361,129	45,439,666	37,315,393
Net loss per share—basic and diluted	$ (0.36)	$ (1.88)	$ (2.02)	$ (3.40)