Summary of Stock Options Issued Pursuant to Stock Incentive Plans (Detail) (USD $)	6 Months Ended
	Jun. 30, 2014
Number of Shares
Outstanding, Beginning Balance	7,408,821
Granted	27,132
Exercised	(542,391)
Forfeited or expired	(62,895)
Outstanding, Ending Balance	6,830,667
Number of Shares Exercisable, Ending Balance	5,002,719
Weighted-Average Exercise Price
Beginning Balance	$ 11.02
Granted	$ 20.13
Exercised	$ 7.57
Forfeited or expired	$ 17.25
Ending Balance	$ 11.28
Weighted Average Exercise Price Exercisable, Ending Balance	$ 9.19
Weighted-Average Remaining Contractual Term (Years)
Weighted Average Remaining Contractual Term (Years), Outstanding as of end of period	5 years 5 months 5 days
Weighted Average Remaining Contractual Term (Years), Exercisable as of end of period	4 years 2 months 9 days
Aggregate Intrinsic Value of In-the-Money Options
Aggregate Intrinsic Value of In-the-Money Options, Outstanding as of end of period	$ 51,913,490
Aggregate Intrinsic Value of In-the-Money Options, Exercisable as of end of period	$ 47,115,588