Share Based Compensation (Details) (USD $)	12 Months Ended
Dec. 31, 2011 Y	Dec. 31, 2010 Y	Dec. 31, 2009 Y
Weighted Average Estimated Fair Value
Weighted average estimated fair value	$ 13.88	$ 11.13	$ 7.35
Quarterly dividend rate	$ 0.29	$ 0.28	$ 0.28
Expected term of the SAR, in years	4.3	4.3	4.3
Risk free interest rate	1.60%	2.00%	1.70%
Dividend yield	3.40%	4.30%	6.60%
Expected stock price volatility	41.90%	41.80%	36.00%
Present value of dividends	$ 4.76	$ 4.55	$ 4.58

The weighted average fair value of nonvested awards on equity-based plans excluding option plans (for example, phantom stock or unit plan, stock or unit appreciation rights plan, revenue or profit achievement stock award plan) for which the employer is contingently obligated to issue equity instruments or transfer assets to an employee who has not yet satisfied service or performance criteria necessary to gain title to proceeds from the sale of the award or underlying shares or units.

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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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- Definition

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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