Summary of Stock Options Issued Pursuant to Stock Incentive Plans (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Number of Shares
Outstanding, Beginning Balance	5,282,693	7,408,821	8,905,746
Granted	2,055,514	27,132	1,208,019
Exercised	(1,144,273)	(2,036,558)	(2,478,183)
Forfeited	(394,265)	(116,702)	(225,474)
Expired	(593)		(1,287)
Outstanding, Ending Balance	5,799,076	5,282,693	7,408,821
Number of Shares Exercisable, Ending Balance	3,744,383
Weighted-Average Exercise Price
Beginning Balance	$ 12.06	$ 11.02	$ 9.05
Granted	19.12	20.13	19.30
Exercised	10.62	8.08	7.81
Forfeited	19.06	17.80	12.79
Expired	20.51		9.65
Ending Balance	14.37	$ 12.06	$ 11.02
Weighted-Average Exercise Price Exercisable, Ending Balance	$ 11.67
Weighted-Average Remaining Contractual Term (Years)
Term of outstanding options	6 years 3 months 7 days
Weighted-Average Remaining Contractual Term (Years), Exercisable as of end of period	4 years 9 months 26 days
Aggregate Intrinsic Value of In-the-Money Options
Aggregate Intrinsic Value of In-the-Money Options, Outstanding as of end of period	$ 40,786,575
Aggregate Intrinsic Value of In-the-Money Options, Exercisable as of end of period	$ 36,424,252