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Summary Of Significant Accounting Policies (Summary Of Weighted-Average Assumptions Used To Value Option Grants) (Details)	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Summary Of Significant Accounting Policies [Abstract]
Expected term of options	6 years 3 months 18 days	6 years 2 months 12 days	7 years
Expected volatility	42.00%	41.00%	40.00%
Risk-free interest rate	1.305%	2.674%	2.94%
Dividend yield	0.00%	0.00%	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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