Stock Option Activity (Detail) (USD $)	3 Months Ended
	Mar. 31, 2012 Year
Number of Options
Outstanding at beginning of period	6,342,337
Granted	983,755
Exercised	(336,436)
Cancelled or expired	(16,435)
Outstanding at end of period	6,973,221
Exercisable at end of period	3,981,153
Vested and expected to vest in the future at end of period	6,174,592
Weighted Average Exercise Price per Share
Outstanding at beginning of period	$ 50.06
Granted	$ 86.22
Exercised	$ 37.14
Cancelled or expired	$ 57.94
Outstanding at end of period	$ 55.74
Exercisable at end of period	$ 44.43
Vested and expected to vest in the future at end of period	$ 53.35
Weighted Average Remaining Contractual Life (in years)
Outstanding at end of period	6.81
Exercisable at end of period	5.56
Vested and expected to vest in the future at end of period	6.56
Aggregate Intrinsic Value
Outstanding at end of period	$ 198,903,742
Exercisable at end of period	156,678,425
Vested and expected to vest in the future at end of period	$ 190,203,151