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Stock Based Compensation - Additional Information (Detail) (USD $)
In Millions, except Share data, unless otherwise specified
9 Months Ended 3 Months Ended
Sep. 30, 2012
Y
Sep. 30, 2012
Performance share units
Mar. 31, 2012
Performance share units
Mar. 31, 2011
Performance share units
Mar. 31, 2012
Performance share units
Maximum
Mar. 31, 2011
Performance share units
Maximum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]            
Stock options vesting period 4 years          
Stock options remaining contractual term 10          
Number of performance share units     352,000 392,500    
Performance share units vesting date         Dec. 31, 2016 Dec. 31, 2016
Unrecognized stock compensation expense   $ 11.5