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Commitments and Contingencies - Additional Information (Detail) (USD $)
 0 Months Ended 3 Months Ended 12 Months Ended
Jan. 31, 2013
Dec. 31, 2012
Dec. 31, 2013
Dec. 31, 2012
Dec. 31, 2011
Loss Contingencies [Line Items]          
Operating leases expiring at various dates through     2028    
Rent expense     $ 46,400,000 $ 51,200,000 $ 49,500,000
Rent abatement credits   1,700,000      
Capital commitments     5,100,000    
Minimum estimated range of aggregate loss for legal proceedings     0    
Maximum estimated range of aggregate loss for legal proceedings     25,000,000    
Eligible investor subject to future buyback principal value     126,200,000    
Eligible investor subject to future buyback potential additional losses related to valuation adjustments     0    
Period of auction rates security to be purchased from rendering of the award     30 days    
Contingency damages amount 30,000,000        
Claim amount including interest and costs 140,000,000        
Initial claim amount including interest and costs 253,000,000        
Auction Rate Securities [Member]
          
Loss Contingencies [Line Items]          
Total amount of ARS the firm purchased and hold     91,600,000    
Amount of ARS committed to purchase from clients     29,100,000    
ARS in firm proprietary account     150,000    
Fair amount of ARS committed to purchase from clients     26,500,000    
Auction rate securities derivative liability     $ 2,600,000    
Office Building [Member]
          
Loss Contingencies [Line Items]          
Number of principal offices   2   2