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Share-Based Compensation (Details) (USD $)	3 Months Ended
Share-Based Compensation (Details) (USD $)	Mar. 31, 2012 Y	Mar. 31, 2011 Y
Weighted-average assumptions for options issued during the indicated periods
Dividend yield	0.00%	0.00%
Expected volatility	61.20%	58.80%
Risk-free interest rate	0.80%	1.90%
Expected life of options (in years)	4.4	3.9
Weighted-average grant-date fair value	$ 15.96	$ 19.33

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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