Basic and Diluted Net Loss Per Share - Summary of Calculation of Basic and Diluted Net Loss Per Share (Detail) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended
	Mar. 31, 2014	Mar. 31, 2013
Numerator
Net loss	$ (34,681)	$ (26,525)
Denominator
Weighted-average number of common shares used in net loss per share calculation	69,214,669	61,572,119
Less: Weighted-average shares subject to repurchase	(1,789)	(29,610)
Denominator: basic and diluted	69,212,880	61,542,509
Net loss per share, basic and diluted	$ (0.50)	$ (0.43)