Combined Stock Option Activity (Detail) (USD $) In Thousands, except Per Share data, unless otherwise specified	12 Months Ended
Dec. 31, 2012
Number of shares
Beginning Balance	2,532
Granted	1,818
Exercised	(371)
Forfeited/Cancelled	(82)
Ending Balance	3,897
Vested and expected to vest as December 31, 2012	3,300
Exercisable as of December 31, 2012	1,639
Weighted Average Exercise Price
Beginning Balance	$ 15.46
Granted	$ 22.87
Exercised	$ 8.64
Forfeited/Cancelled	$ 27.19
Ending Balance	$ 19.32
Vested and expected to vest as December 31, 2012	$ 18.44
Exercisable as of December 31, 2012	$ 12.78
Weighted average remaining contractual term
Vested and expected to vest as December 31, 2012	6 years 8 months 12 days
Exercisable as of December 31, 2012	3 years 10 months 24 days
Aggregate Intrinsic Value
Vested and expected to vest as December 31, 2012	$ 19,728
Exercisable as of December 31, 2012	$ 18,605

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