Nature of Business and Significant Accounting Policies (Details 5)	12 Months Ended
Dec. 31, 2011 Years	Dec. 31, 2010 Years	Dec. 31, 2009 Years
Stock Option Awards
Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Method Used [Line Items]
Risk-free interest rate	1.00%	1.60%	1.50%
Expected dividend yield	0.70%	0.00%	0.00%
Expected term	4.3	4.3	4.3
Expected volatility	42.30%	45.10%	46.90%
Employee Stock Purchase Plan
Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Method Used [Line Items]
Risk-free interest rate	0.10%	0.20%	0.30%
Expected dividend yield	0.80%	0.00%	0.00%
Expected term	6	6	6
Expected volatility	33.10%	27.10%	49.50%

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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