Shareholders' Equity (Schedule of Assumptions Used to Calculate Fair Value of Options Granted) (Details) (USD $)	12 Months Ended
Dec. 31, 2011 Yr	Dec. 31, 2010 Yr	Dec. 31, 2009 Yr
Shareholders' Equity
Risk-free interest rate	1.70%	2.00%	3.10%
Dividend yield	3.50%	5.40%	6.00%
Volatility factor	37.20%	36.00%	29.10%
Expected life (in years)	7.4	7.2	7.1
Fair value of options per share	$ 7.45	$ 5.60	$ 2.59

The period of time an equity-based award is expected to be outstanding. An equity-based award's expected term is generally determined based on, among other factors, the instrument's contractual term and the effects of employees' expected exercise and post-vesting employment termination behavior.

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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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