(Black-Scholes Pricing Model Assumptions) (Details) (USD $)	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Assumptions of Black-Scholes option pricing model
Expected dividend yield	3.60%	3.50%	3.50%
Risk-free interest rate	1.18%	2.76%	3.37%
Expected stock price volatility	44.40%	42.00%	41.10%
Expected life of options - in years	6 years 1 month 10 days	6 years 1 month 6 days	6 years 3 months 29 days
Weighted average fair value per share	$ 7.08	$ 6.12	$ 7.65