Stock-Based Compensation (Schedule of Valuation Assumptions) (Details)	3 Months Ended	6 Months Ended
Jun. 30, 2011	Jun. 30, 2010	Jun. 30, 2011	Jun. 30, 2010
Stock-Based Compensation
Risk-free interest rate	1.40%	1.70%	1.90%	2.30%
Dividend yield	0.20%	0.50%	0.30%	0.50%
Volatility factor	45.00%	46.00%	44.00%	43.00%
Expected life (in years)	3.8	3.8	4.3	4.7

The period of time an equity-based award is expected to be outstanding. An equity-based award's expected term is generally determined based on, among other factors, the instrument's contractual term and the effects of employees' expected exercise and post-vesting employment termination behavior.

+ References+ Details

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.

+ References+ Details