Basic and Diluted Net Loss Per Share (Detail) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011
Numerator
Net loss	$ (19,282)	$ (22,038)	$ (46,743)	$ (60,199)
Denominator
Weighted average common shares outstanding	90,370	37,320	73,790	35,132
Weighted average shares subject to repurchase	0	0	0	(5)
Weighted average shares outstanding, basic and diluted	90,370	37,320	73,790	35,127
Basic and diluted net loss per share	$ (0.21)	$ (0.59)	$ (0.63)	$ (1.71)