Stock-Based Compensation Stock Option Black Scholes Option Pricing Model Assumptions (Details) (Employee Stock Option [Member])	3 Months Ended
Mar. 31, 2012	Mar. 31, 2011
Employee Stock Option [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis, Valuation Techniques [Line Items]
Dividend yield	0.00%	0.00%
Expected volatility	42.70%	46.60%
Risk free interest rate	0.90%	2.00%
Expected life (years)	5.14	4.85

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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