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Acquisition Of Walker Group Holdings Llc - Additional Information (Detail) (USD $)
 12 Months Ended
Dec. 31, 2012
Dec. 31, 2011
Dec. 31, 2010
May 08, 2012
Apr. 23, 2012
Unsecured Debt
Convertible Senior Notes
Business Acquisition [Line Items]          
Walker acquisition, Purchase price       $ 375,000,000  
ACQUISITION EXPENSES 14,409,000 0 0    
Intangibles       162,800,000  
Goodwill 146,400,000     146,444,000  
Acquisition of equity interests of Walker, revenue from date of acquisition 270,100,000        
Acquisition of equity interests of Walker, net income from date of acquisition $ 34,300,000        
Notes issued, interest rate         3.375%
Notes issued, due date         2018