- Stock Option Activity and Weighted Average Exercise Price (Detail) - $ / shares	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Outstanding Shares
Forfeited	0
Stock Option Plans
Outstanding Shares
Beginning Balance	4,717,061	4,105,539	4,206,512
Granted	1,267,812	1,326,430	743,062
Exercised	(898,417)	(348,206)	(706,750)
Forfeited	(192,505)	(366,702)	(137,285)
Ending Balance	4,893,951	4,717,061	4,105,539
Vested or expected to vest at end of period	4,893,951
Options exercisable at end of period	1,921,189
Weighted-Average Exercise Price
Beginning Balance	$ 84.32	$ 84.61	$ 66.38
Granted	88.22	78.72	150.81
Exercised	44.18	40.51	40.21
Forfeited	108.15	108.90	112.95
Ending Balance	91.78	$ 84.32	$ 84.61
Vested or expected to vest at end of period	91.78
Options exercisable at end of period	$ 88.21
Omnibus Incentive Plan
Outstanding Shares
Beginning Balance	0	18,950	63,233
Exercised	0	(18,950)	(44,283)
Forfeited		0	0
Ending Balance	0	0	18,950
Vested or expected to vest at end of period	0
Options exercisable at end of period	0
Weighted-Average Exercise Price
Beginning Balance	$ 0.00	$ 23.37	$ 23.76
Exercised	0.00	23.37	23.92
Forfeited	0.00	0.00
Ending Balance	0.00	$ 0.00	$ 23.37
Vested or expected to vest at end of period	0.00
Options exercisable at end of period	$ 0.00