Summary of Option Activities (Detail) (USD $)	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Outstanding Option, Number of shares, beginning balance	7,558,945	6,594,950	8,802,450
Granted, Number of Shares	2,966,850	2,894,500	94,000
Exercised, Number of Shares	(2,608,007)	(1,563,255)	(2,000,250)
Cancelled, Number of Shares	(481,550)	(367,250)	(301,250)
Outstanding Option, Number of shares, ending balance	7,436,238	7,558,945	6,594,950
Outstanding Option, Average Option Price, beginning balance	$ 31.63	$ 25.16	$ 25.03
Outstanding options vested and exercisable, Number of Shares	2,185,312
Granted, Average Option Price	$ 37.01	$ 43.66	$ 30.40
Exercised, Average Option Price	$ 23.22	$ 26.38	$ 24.87
Cancelled, Average Option Price	$ 38.00	$ 32.60	$ 24.91
Outstanding Option, Average Option Price, ending balance	$ 36.31	$ 31.63	$ 25.16
Outstanding options vested and exercisable, Average Option Price	$ 30.40
Thirty One Point Seven Zero To Sixteen Point Two Two
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Range, High			$ 31.70
Range, Low			$ 16.22
Thirty Two Point Two Eight To Thirty Point Three Two
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Range, High			$ 32.28
Range, Low			$ 30.32
Thirty One Point One Eight To Sixteen Point Two Two
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Range, High	$ 44.83		$ 31.18
Range, Low	$ 36.95		$ 16.22
Thirty Two Point Two Eight To Sixteen Point Two Two
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Range, High	$ 46.97	$ 32.28	$ 32.28
Range, Low	$ 16.22	$ 16.22	$ 16.22
Fifty Four Point Seven Nine To Thirty Eight Point One Two
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Range, High	$ 54.79	$ 54.79
Range, Low	$ 16.22	$ 38.12
Forty Six Point Nine Seven To Sixteen Point Two Two
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Range, High	$ 46.97	$ 46.97
Range, Low	$ 16.22	$ 16.22
Fifty Four Point Seven Nine To Sixteen Point Two Two
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Range, High	$ 54.79	$ 54.79
Range, Low	$ 16.22	$ 16.22