Additional Information about Stock Options Outstanding (Detail) (USD $)	12 Months Ended
	Dec. 31, 2011 Year
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Options Outstanding, No. of Options	5,434,228
Options Outstanding, Avg. Life in Years	4.1
Options Outstanding, Aggregate Intrinsic Value	$ 30,975,000
Options Exercisable, No. of Options	2,319,735
Options Exercisable, Avg. Life in Years	2.3
Options Exercisable, Aggregate Intrinsic Value	22,244,000
Range of Exercise Prices per Option $19.43 to $23.58
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Options Outstanding, No. of Options	393,750
Options Outstanding, Avg. Life in Years	1.0
Options Outstanding, Aggregate Intrinsic Value	13,571,000
Options Exercisable, No. of Options	393,750
Options Exercisable, Avg. Life in Years	1.0
Options Exercisable, Aggregate Intrinsic Value	13,571,000
Range of Exercise Prices per Option $19.43 to $23.58 | Minimum
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Range of exercise prices	$ 19.43
Range of Exercise Prices per Option $19.43 to $23.58 | Maximum
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Range of exercise prices	$ 23.58
Range of Exercise Prices per Option $30.30 to $45.23
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Options Outstanding, No. of Options	953,610
Options Outstanding, Avg. Life in Years	3.6
Options Outstanding, Aggregate Intrinsic Value	11,466,000
Options Exercisable, No. of Options	541,235
Options Exercisable, Avg. Life in Years	3.2
Options Exercisable, Aggregate Intrinsic Value	6,604,000
Range of Exercise Prices per Option $30.30 to $45.23 | Minimum
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Range of exercise prices	$ 30.30
Range of Exercise Prices per Option $30.30 to $45.23 | Maximum
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Range of exercise prices	$ 45.23
Range of Exercise Prices per Option $51.07 to $57.32
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Options Outstanding, No. of Options	2,067,156
Options Outstanding, Avg. Life in Years	3.9
Options Outstanding, Aggregate Intrinsic Value	5,938,000
Options Exercisable, No. of Options	730,750
Options Exercisable, Avg. Life in Years	1.7
Options Exercisable, Aggregate Intrinsic Value	2,069,000
Range of Exercise Prices per Option $51.07 to $57.32 | Minimum
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Range of exercise prices	$ 51.07
Range of Exercise Prices per Option $51.07 to $57.32 | Maximum
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Range of exercise prices	$ 57.32
Range of Exercise Prices per Option $67.64 to $72.75
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Options Outstanding, No. of Options	2,019,712
Options Outstanding, Avg. Life in Years	5.1
Options Outstanding, Aggregate Intrinsic Value	0
Options Exercisable, No. of Options	654,000
Options Exercisable, Avg. Life in Years	3.1
Options Exercisable, Aggregate Intrinsic Value	$ 0
Range of Exercise Prices per Option $67.64 to $72.75 | Minimum
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Range of exercise prices	$ 67.64
Range of Exercise Prices per Option $67.64 to $72.75 | Maximum
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Range of exercise prices	$ 72.75