Assumptions for Stock Options Granted (Detail) (USD $)	12 Months Ended
	Dec. 31, 2012 Y	Dec. 31, 2011 Y	Dec. 31, 2010 Y
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Expected volatility, Minimum	42.23%	39.64%	35.56%
Expected volatility, Maximum	43.17%	41.09%	39.89%
Risk-free rate, Minimum	0.83%	1.24%	1.73%
Risk-free rate, Maximum	1.03%	2.76%	3.29%
Weighted-average volatility	42.71%	40.45%	37.76%
Weighted-average dividends	1.14%	1.04%	1.75%
Weighted-average term (in years)	5.86	5.86	5.43
Weighted-average risk-free rate	0.93%	1.97%	2.45%
Weighted-average grant date fair value	$ 12.83	$ 14.55	$ 7.33
Minimum
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Expected dividends	1.10%	0.90%	1.50%
Expected term (in years)	5 years 9 months	5 years 7 months 28 days	4 years 6 months
Maximum
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Expected dividends	1.18%	1.19%	1.80%
Expected term (in years)	6 years	5 years 10 months 21 days	6 years 6 months