Stock Option Activity (Detail) (USD $) In Thousands, except Per Share data, unless otherwise specified	12 Months Ended
Dec. 31, 2012
Number of options
Options outstanding at December 31, 2011	3,304
Granted	1,910
Exercised	(294)
Canceled/forfeited/expired	(258)
Options outstanding at December 31, 2012	4,662
Vested or expected to vest at December 31, 2012	4,576
Exercisable at December 31, 2012	2,265
Weighted average exercise price
Options outstanding at December 31, 2011	$ 0.80
Granted	$ 4.07
Exercised	$ 0.47
Canceled/forfeited/expired	$ 2.18
Options outstanding at December 31, 2012	$ 2.08
Vested or expected to vest at December 31, 2012	$ 2.05
Exercisable at December 31, 2012	$ 0.71
Weighted average remaining contactual term
Options outstanding at December 31, 2012	7 years 10 months 21 days
Vested or expected to vest at December 31, 2012	7 years 10 months 10 days
Exercisable at December 31, 2012	6 years 5 months 9 days
Aggregate intrinsic value
Options outstanding at December 31, 2012	$ 19,665
Vested or expected to vest at December 31, 2012	19,453
Exercisable at December 31, 2012	$ 12,668

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