Schedule of Weighted Average Option Fair Values and Assumptions (Detail) (USD $)	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Schedule of Weighted Average Assumptions for Fair Values of Stock Options[Line Items]
Weighted average fair value of grants	$ 11.40	$ 12.30	$ 9.56
Dividend yield	1.59%	1.46%	1.51%
Volatility	32.00%	32.72%	33.43%
Expected life (in years)	5 years 11 months 23 days	6 years 1 month 21 days	5 years 11 months 23 days
Minimum
Schedule of Weighted Average Assumptions for Fair Values of Stock Options[Line Items]
Risk-free interest rate	0.17%	0.28%	0.32%
Maximum
Schedule of Weighted Average Assumptions for Fair Values of Stock Options[Line Items]
Risk-free interest rate	3.96%	5.61%	5.67%