Stock Option Plans - Assumptions Used to Value Option Grants (Details)	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Expected life in years	5 years	5 years
Interest rate, minimum	0.60%	0.91%
Interest rate, maximum	0.92%	2.10%
Volatility, minimum	0.327%	0.327%
Volatility, maximum	0.333%	0.33%
Dividend yield	2.50% - 2.70%	2.37% - 2.70%