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Stock-Based Compensation - Additional Information (Detail) (Restricted stock units, USD $)
In Millions, except Share data, unless otherwise specified
9 Months Ended
Sep. 30, 2012
Restricted stock units
 
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]  
Restricted stock units granted in shares 287,604
Fair value of restricted stock units $ 12.2