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Shareholders' Equity Transactions Assumptions (Details)	12 Months Ended
Shareholders' Equity Transactions Assumptions (Details)	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Expected dividend yield	0.40%	0.20%	0.21%
Expected stock price volatility	41.00%	37.30%	39.60%
Risk free interest rate	0.94%	1.11%	1.57%
Expected life in years	6 years 0 months 13 days	5 years 10 months 13 days	3 years 10 months 13 days
Forfeiture percentage	7.60%	6.90%	10.50%

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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