Schedule of Weighted Average Option, Performance Share Fair Values and Assumptions (Detail) (USD $)	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012
Schedule of Weighted Average Assumptions for Fair Values of Stock Options[Line Items]
Weighted average fair value of option grants	$ 13.28	$ 11.23	$ 12.85	$ 11.44
Dividend yield	1.51%	1.83%	1.57%	1.58%
Volatility	30.76%	31.91%	30.94%	32.01%
Expected life (in years)	5 years 10 months 2 days	5 years 11 months 1 day	5 years 10 months 13 days	5 years 11 months 23 days
Performance Shares
Schedule of Weighted Average Assumptions for Fair Values of Stock Options[Line Items]
Weighted average fair value of option grants	$ 50.45		$ 50.45
Dividend yield	0.00%		0.00%
Volatility	28.99%		28.99%
Risk-free forward interest rate	0.40%		0.40%
Expected life (in years)	2 years 10 months 13 days		2 years 10 months 13 days
Minimum
Schedule of Weighted Average Assumptions for Fair Values of Stock Options[Line Items]
Risk-free forward interest rate	0.14%	0.19%	0.17%	0.17%
Maximum
Schedule of Weighted Average Assumptions for Fair Values of Stock Options[Line Items]
Risk-free forward interest rate	3.94%	3.99%	4.10%	3.98%