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Stock Based Incentive Plan - Aggregated Assumptions Used to Estimate Fair Value of Options Granted (Details 1) (USD $)	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Aggregated assumptions used to estimate fair value of options granted
Expected option life in years	8 years 2 months 12 days	7 years 10 months 24 days	8 years
Risk free interest rate	1.63%	3.04%	3.60%
Expected dividend yield	5.40%	4.64%	4.55%
Expected volatility	50.74%	49.11%	47.16%
Fair value of options	$ 4.37	$ 5.72	$ 5.81

The estimated measure of the percentage by which a share price is expected to fluctuate during a period. Volatility also may be defined as a probability-weighted measure of the dispersion of returns about the mean. The volatility of a share price is the standard deviation of the continuously compounded rates of return on the share over a specified period. That is the same as the standard deviation of the differences in the natural logarithms of the stock prices plus dividends, if any, over the period.

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