Net Loss Per Share - Summary of Basic and Diluted Net Loss Per Share (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Numerator:
Net loss attributable to common stockholders									$ (158,987)	$ (94,495)	$ (36,105)
Denominator:
Weighted average common stock outstanding—basic									33,492,795	27,778,288	21,574,347
Dilutive effect of shares of common stock equivalents resulting from common stock options and preferred common stock (as converted)									0	0	0
Weighted average common stock outstanding—diluted									33,492,795	27,778,288	21,574,347
Net loss per share attributable to common stockholders—basic and diluted	$ (1.50)	$ (1.15)	$ (1.08)	$ (0.97)	$ (0.99)	$ (0.84)	$ (0.90)	$ (0.66)	$ (4.75)	$ (3.40)	$ (1.67)