Computation of 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, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Numerator:
Net loss	$ (1,937)	$ (9,363)	$ (21,304)	$ (29,887)
Denominator:
Weighted average shares used to compute basic and diluted net loss per share	32,383	31,185	31,930	30,848
Basic and diluted net loss per share	$ (0.06)	$ (0.30)	$ (0.67)	$ (0.97)