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Compensation Expense Associated with the Stock-Settled Performance Units (Detail) (Stock Settled Performance Units, USD $)
In Thousands, unless otherwise specified
3 Months Ended 6 Months Ended
Jun. 30, 2012
Jun. 30, 2011
Jun. 30, 2012
Jun. 30, 2011
Stock Settled Performance Units
       
Unrecognized Share Based Compensation Expense [Line Items]        
Stock-based compensation expense associated with Stock-Settled Performance Units $ 979 $ 724 $ 1,703 $ 983