Net Loss per Share - Calculation of Basic and Diluted Net Loss Per Share of Common Stock Attributable to Company's Common Stockholders (Detail) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Numerator:
Net loss	$ (21,060)	$ (11,415)	$ (58,339)	$ (20,308)
Deemed dividend related to the beneficial conversion feature of Series F convertible preferred stock			(14,840)
Net loss attributable to common stockholders	(21,060)	(11,415)	(73,179)	(20,308)
Net loss attributable to preferred stockholders	1,183		3,329
Net loss attributable to common stockholders - basic and diluted	$ (19,877)	$ (11,415)	$ (69,850)	$ (20,308)
Denominator:
Weighted average common shares outstanding, basic and diluted	33,609,212	8,005,142	29,664,548	2,828,757
Net loss per share attributable to common stockholders, basic and diluted	$ (0.59)	$ (1.43)	$ (2.35)	$ (7.18)