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Summary of Significant Accounting Policies (Details 2)			12 Months Ended
Summary of Significant Accounting Policies (Details 2)	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2011 Stock options	Dec. 31, 2010 Stock options
Fair Value of Option Grants, Assumptions and Methodology
Dividend yield (as a percent)			0.00%	0.00%
Risk free interest rate (as a percent)			2.00%	1.50%
Expected volatility (as a percent)			40.00%	44.00%
Expected life			4 years 9 months 4 days	4 years
Common Stock Held in Treasury, at Cost
Number of shares of common stock held in treasury	14,677,872	12,679,948

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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