Summary of Stock Option Activity under Plans and Related Information (Detail) (USD $) In Thousands, except Share data, unless otherwise specified	12 Months Ended
	Dec. 31, 2013
Number of stock options outstanding
Beginning Balance	9,521,970
Granted	2,342,729
Exercised	(1,114,819)
Forfeited, cancelled or expired	(792,513)
Ending Balance	9,957,367
Options vested and exercisable at December 31, 2013	5,639,981
Options vested and expected to vest as of December 31, 2013	9,358,952
Weighted-Average Exercise Price
Beginning Balance	$ 8.13
Granted	$ 9.08
Exercised	$ 3.30
Forfeited, cancelled or expired	$ 10.36
Ending Balance	$ 8.72
Options vested and exercisable at December 31, 2013	$ 7.95
Options vested and expected to vest as of December 31, 2013	$ 8.65
Weighted-Average Remaining Contractual Term
Balance at December 31, 2013	7 years 8 months 12 days
Options vested and exercisable at December 31, 2013	7 years 2 months 12 days
Aggregate Intrinsic Value
Balance at December 31, 2013	$ 28,262
Options vested and exercisable at December 31, 2013	21,101
Options vested and expected to vest as of December 31, 2013	$ 27,280