(Black-Scholes Pricing Model Assumptions) (Details) - $ / shares	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Assumptions of Black-Scholes option pricing model
Expected dividend yield	3.50%	3.00%	3.50%
Risk-free interest rate	1.78%	2.16%	1.34%
Expected stock price volatility	39.10%	42.20%	42.10%
Expected life of options - in years	7 years	7 years	7 years
Weighted average fair value per share	$ 8.40	$ 9.64	$ 7.40