Weighted-Average Assumptions (Detail) (Stock Options)	12 Months Ended
Dec. 31, 2011 Year	Dec. 31, 2010 Year	Dec. 31, 2009 Year
Stock Options
Deferred Compensation Arrangement with Individual, Share-based Payments [Line Items]
Risk-free interest rate	2.26%	2.12%	2.03%
Expected volatility	41.00%	54.00%	78.00%
Expected life of the option in years	4.60	4.64	4.63
Expected dividend yield	0.00%	0.00%	0.00%

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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