Share-based Compensation - Black-Scholes Assumptions (Details) (USD $)	3 Months Ended	9 Months Ended
Sep. 30, 2012 Y	Sep. 30, 2011 Y	Sep. 30, 2012 Y	Sep. 30, 2011 Y
Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions and Methodology [Abstract]
Risk-free interest rate, average	1.10%	1.40%	1.30%	1.70%
Expected option life, average (in years)	7.3	7.1	7.2	7.0
Expected price volatility, average	51.10%	51.90%	51.40%	51.80%
Expected dividend yield	0.00%	0.00%	0.00%	0.00%
Weighted average per share fair value (in dollars per share)	$ 2.13	$ 3.35	$ 2.19	$ 3.16

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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