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Special Charges - Additional Information (Detail) (USD $)
 3 Months Ended 12 Months Ended
Mar. 31, 2013
Dec. 31, 2012
Employee
Location
Special Charges [Line Items]    
Special charges $ 427,000 $ 29,600,000
Non cash special charges   5,000,000
Number of employees terminated   116
Number of office locations   9
Cash outflow associated with special charges, amount paid 24,900,000  
Cash outflow associated with special charges, amount paid 10,900,000  
Cash outflow associated with special charges, amount expected to be paid in 2013 5,600,000  
Cash outflow associated with special charges, amount expected to be paid in 2014 2,700,000  
Cash outflow associated with special charges, amount expected to be paid in 2015 1,200,000  
Cash outflow associated with special charges, amount expected to be paid in 2016 800,000  
Cash outflow associated with special charges, amount expected to be paid from 2017 to 2025 $ 3,700,000