Schedule of Employee Options Outstanding and Exercisable (Detail) (USD $)	12 Months Ended
	Dec. 31, 2012
Range 1
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Range of Exercise Prices, Lower limit	$ 14.94
Range of Exercise Prices, Upper limit	$ 28.88
Options Outstanding, Number	263,195
Options Outstanding, Weighted Average Remaining Contractual Lives	7 months 24 days
Options Outstanding, Weighted Average Exercise Price	$ 23.37
Options Currently Exercisable, Number	263,195
Options Currently Exercisable, Weighted Average Exercise Price	$ 23.37
Range 2
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Range of Exercise Prices, Lower limit	$ 30.29
Range of Exercise Prices, Upper limit	$ 34.19
Options Outstanding, Number	387,750
Options Outstanding, Weighted Average Remaining Contractual Lives	6 years 1 month 24 days
Options Outstanding, Weighted Average Exercise Price	$ 34.11
Options Currently Exercisable, Number	189,500
Options Currently Exercisable, Weighted Average Exercise Price	$ 34.11
Range 3
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Range of Exercise Prices, Lower limit	$ 35.00
Range of Exercise Prices, Upper limit	$ 36.50
Options Outstanding, Number	362,913
Options Outstanding, Weighted Average Remaining Contractual Lives	2 years 11 days
Options Outstanding, Weighted Average Exercise Price	$ 36.17
Options Currently Exercisable, Number	362,913
Options Currently Exercisable, Weighted Average Exercise Price	$ 36.17
Range 4
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Range of Exercise Prices, Lower limit	$ 36.81
Options Outstanding, Number	496,500
Options Outstanding, Weighted Average Remaining Contractual Lives	9 years 22 days
Options Outstanding, Weighted Average Exercise Price	$ 36.81
Range 5
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Range of Exercise Prices, Lower limit	$ 36.88
Range of Exercise Prices, Upper limit	$ 41.10
Options Outstanding, Number	369,195
Options Outstanding, Weighted Average Remaining Contractual Lives	1 year 5 months 12 days
Options Outstanding, Weighted Average Exercise Price	$ 36.95
Options Currently Exercisable, Number	357,195
Options Currently Exercisable, Weighted Average Exercise Price	$ 36.90
Range 6
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Range of Exercise Prices, Lower limit	$ 42.15
Range of Exercise Prices, Upper limit	$ 44.88
Options Outstanding, Number	301,423
Options Outstanding, Weighted Average Remaining Contractual Lives	6 years 10 months 28 days
Options Outstanding, Weighted Average Exercise Price	$ 42.35
Options Currently Exercisable, Number	21,673
Options Currently Exercisable, Weighted Average Exercise Price	$ 44.87
Range Seven
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Range of Exercise Prices, Lower limit	$ 45.21
Range of Exercise Prices, Upper limit	$ 46.47
Options Outstanding, Number	318,500
Options Outstanding, Weighted Average Remaining Contractual Lives	7 years 8 months 9 days
Options Outstanding, Weighted Average Exercise Price	$ 46.27
Options Currently Exercisable, Number	50,000
Options Currently Exercisable, Weighted Average Exercise Price	$ 45.21
Range Eight
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Range of Exercise Prices, Lower limit	$ 46.28
Range of Exercise Prices, Upper limit	$ 48.46
Options Outstanding, Number	393,406
Options Outstanding, Weighted Average Remaining Contractual Lives	4 years 1 month 10 days
Options Outstanding, Weighted Average Exercise Price	$ 47.84
Options Currently Exercisable, Number	385,906
Options Currently Exercisable, Weighted Average Exercise Price	$ 47.85