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Acquisition of Walker Group Holdings Llc - Additional Information (Detail) (USD $)
 3 Months Ended 6 Months Ended
Jun. 30, 2012
Jun. 30, 2012
May 08, 2012
Business Acquisition [Line Items]      
Acquisition of equity interests of Walker, cash paid     $ 375,000,000
Acquisition of equity interests of Walker, acquisition related costs 12,224,000 13,902,000  
Acquisition of equity interests of Walker, intangible assets recorded     162,100,000
Estimated amortization expense for 2012 13,600,000 13,600,000  
Estimated amortization expense for 2013 17,500,000 17,500,000  
Estimated amortization expense for 2014 17,500,000 17,500,000  
Estimated amortization expense for 2015 17,500,000 17,500,000  
Estimated amortization expense for 2016 17,500,000 17,500,000  
Acquisition of equity interests of Walker, goodwill recorded     151,492,000
Acquisition of equity interests of Walker, revenue from date of acquisition   44,300,000  
Acquisition of equity interests of Walker, net income from date of acquisition   $ 2,900,000