Stock - Based Compensation - Weighted-average assumptions (Detail)	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Risk-free interest rate	1.20%	2.70%	2.80%
Dividend yield	2.70%	1.80%	2.20%
Expected volatility of the Company's common stock	0.644%	0.615%	0.604%
Expected life in years	6 years	6 years	6 years