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Stock-Based Compensation - Simulation Model Input Variables (Details) (Performance Share Awards)	12 Months Ended
	Dec. 31, 2012
Performance Share Awards
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Weighted average assumptions, expected volatility factor	39.00%
Weighted average assumptions, risk-free interest rate	0.44%
Weighted average assumptions, expected term	2 years 8 months 19 days
Weighted average assumptions, expected dividend yield	0.00%

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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