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Stock-Based Compensation (Assumptions Used To Value Option Grants and Stock Awards (Details)	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012
Employee Stock Option [Member]
Expected volatility factor	39.00%	38.00%
Approximate risk free interest rate	0.44%	0.65%
Expected term	3 years 4 months 6 days	3 years 10 months 28 days
Expected dividend yield	0.00%	0.00%
Non-Vested Stock Unit Awards [Member]
Approximate risk free interest rate	0.33%	0.47%
Expected term	2 years 9 months
Expected dividend yield	0.00%	0.00%
Non-Vested Stock Unit Awards [Member] \| Minimum [Member]
Expected volatility factor	16.00%	21.00%
Non-Vested Stock Unit Awards [Member] \| Maximum [Member]
Expected volatility factor	42.00%	39.00%

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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