Share-Based Compensation (Share-Based Compensation Valuation Assumptions) (Details) (Stock Options [Member], USD $) In Thousands, except Per Share data, unless otherwise specified	12 Months Ended
Dec. 31, 2011 years	Dec. 31, 2010 years	Dec. 31, 2009 years
Stock Options [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock option expense for the year	$ 3,445	$ 3,164	$ 3,432
Aggregate exercise date intrinsic value of options exercised during the year	$ 23,703	$ 34,171	$ 1,851
Expected life of options in years, based upon historical experience	5	5	5
Risk-free interest rate	1.20%	2.30%	1.90%
Expected volatility, based upon historical volatility	18.80%	14.50%	15.60%
Expected dividend yield	3.30%	3.90%	6.70%
Average estimated value of options granted during the year	$ 13.01	$ 7.16	$ 2.05

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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- Definition

The noncash expense that accounts for the value of stock or unit options distributed to employees as compensation.

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