Accounting for Stock-Based Compensation (Details 1) (USD $) In Thousands, unless otherwise specified	12 Months Ended
Dec. 31, 2011 Y	Dec. 31, 2010 Y	Dec. 31, 2009 Y
Fair value of stock options
Expected volatility	33.80%	33.70%	40.70%
Expected dividends	$ 0	$ 0	$ 0
Expected term	4	3.1	4
Risk-free interest rate	1.63%	1.41%	1.64%

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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