Fair Value of Option Award Estimated on Date of Grant using Black-Scholes Pricing Model (Detail) (Stock Options, USD $)	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2012 Minimum	Dec. 31, 2012 Maximum
Share based Compensation Arrangement by Share based Payment Award, Fair Value Assumptions, Method Used [Line Items]
Fair value per option grant	$ 20.34	$ 18.75	$ 12.37	$ 17.74
Assumptions
Dividend yield	1.80%	1.80%	1.80%	2.27%
Expected volatility	37.00%	43.00%	39.00%	39.62%
Risk-free interest rate	2.10%	2.52%	0.55%	0.77%
Expected life	5 years 1 month 6 days	5 years 3 months	4 years	5 years 2 months 12 days