Stockholders' Equity (Fair Value Assumptions for Options Granted) (Details) (USD $)	6 Months Ended
Jun. 30, 2011
April 19, 2011 [Member]
Risk-free interest rate	2.10%
Expected life of option in years	5.00
Expected dividend yield	1.60%
Expected stock volatility	39.33%
Estimated fair value of stock option	$ 11.20
April 20, 2010 [Member]
Risk-free interest rate	2.60%
Expected life of option in years	5.00
Expected dividend yield	1.50%
Expected stock volatility	39.10%
Estimated fair value of stock option	$ 8.14
April 21, 2009 [Member]
Risk-free interest rate	1.90%
Expected life of option in years	5.00
Expected dividend yield	1.00%
Expected stock volatility	38.80%
Estimated fair value of stock option	$ 3.64
April 15, 2008 [Member]
Risk-free interest rate	2.70%
Expected life of option in years	5.00
Expected dividend yield	1.00%
Expected stock volatility	30.93%
Estimated fair value of stock option	$ 7.75
April 17, 2007 [Member]
Risk-free interest rate	4.60%
Expected life of option in years	4.85
Expected dividend yield	1.00%
Expected stock volatility	31.59%
Estimated fair value of stock option	$ 5.68

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.

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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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