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SHARE-BASED COMPENSATION - Weighted Average Assumptions Used in Estimating the Value of Performance Share Units Granted (Details) (USD $)
12 Months Ended
Dec. 31, 2011
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]  
Risk-free rate minimum 0.12%
Risk-free rate maximum 0.80%
Volatility minimum 28.65%
Volatility maximum 35.74%
Performance share units
 
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]  
Performance period 2/9/2011 – 2/9/2013
Valuation date closing stock price 24.32
Expected dividends 2.47%