Stock Option Activity and Weighted Average Exercise Price (Detail) - $ / shares	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Outstanding Shares
Forfeited	0
Stock Option Plans
Outstanding Shares
Beginning Balance	4,206,512	4,466,080	4,330,410
Granted	743,062	705,564	1,037,729
Exercised	(706,750)	(866,917)	(821,679)
Forfeited	(137,285)	(98,215)	(80,380)
Ending Balance	4,105,539	4,206,512	4,466,080
Vested or expected to vest at end of period	4,105,539
Options exercisable at end of period	1,990,346
Weighted-Average Exercise Price
Beginning Balance	$ 66.38	$ 49.29	$ 35.50
Granted	150.81	130.10	87.06
Exercised	40.21	30.33	24.45
Forfeited	112.95	65.14	47.55
Ending Balance	84.61	$ 66.38	$ 49.29
Vested or expected to vest at end of period	84.61
Options exercisable at end of period	$ 48.05
Omnibus Incentive Plan
Outstanding Shares
Beginning Balance	63,233	162,431	353,572
Exercised	(44,283)	(96,398)	(191,141)
Forfeited		(2,800)
Ending Balance	18,950	63,233	162,431
Vested or expected to vest at end of period	18,950
Options exercisable at end of period	18,950
Weighted-Average Exercise Price
Beginning Balance	$ 23.76	$ 23.74	$ 23.47
Exercised	23.92	23.77	23.23
Forfeited	0.00	22.43
Ending Balance	23.37	$ 23.76	$ 23.74
Vested or expected to vest at end of period	23.37
Options exercisable at end of period	$ 23.37
Non Employee Directors, Plan
Outstanding Shares
Beginning Balance	0	0	16,000
Exercised	0	0	(16,000)
Forfeited			0
Ending Balance		0	0
Weighted-Average Exercise Price
Beginning Balance	$ 0.00	$ 0.00	$ 27.10
Exercised	$ 0.00	0.00	27.10
Forfeited			0.00
Ending Balance		$ 0.00	$ 0.00