Employee Benefit Plans - Fair Value Assumptions & Compensation Cost (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
Dec. 31, 2011 Years	Dec. 31, 2010 Years	Dec. 31, 2009 Years
Options Granted [Abstract]
Risk-free interest rate	1.80%	2.80%	3.00%
Expected life at issuance	5.14	6.6	6.7
Expected volatillity	56.70%	58.40%	60.30%
Expected dividends	$ 0	$ 0	$ 0
Share-based compensation expense	$ 6.6	$ 6.1	$ 13.5

Equity-based compensation cost during the period with respect to the award, which will be recognized in income (as well as the total recognized tax benefit) or capitalized as part of the cost of an asset.

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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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- Definition

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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