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Employee Benefit Plans (Options Valuation Assumptions) (Details)	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010
Fair value assumptions:
Expected term of option	5 years 6 months	5 years 6 months
Weighted average risk-free interest rate	2.33%	2.65%
Weighted average expected volatility	31.51%	42.35%
Dividend yield	1.00%	1.25%

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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