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Regulatory requirements - Additional Information (Detail) (USD $)
 9 Months Ended
Sep. 30, 2012
Dec. 31, 2011
Schedule Of Compliance With Regulatory Capital Requirements Under Brokers And Dealers [Line Items]    
Actual percentage of net capital to aggregate customer-related debit items 14.63%  
Freedom maintain net capital equal to the greater $ 250,000  
Aggregate indebtedness 6.67%  
Cash and securities segregated for regulatory and other purposes 29,142,000 30,086,000
Oppenheimer [Member]
    
Schedule Of Compliance With Regulatory Capital Requirements Under Brokers And Dealers [Line Items]    
Required percentage of net capital to aggregate customer-related debit items 2.00%  
Net capital 163,400,000  
Excess net capital 141,100,000  
Cash and securities segregated for regulatory and other purposes 12,500,000  
Freedom [Member]
    
Schedule Of Compliance With Regulatory Capital Requirements Under Brokers And Dealers [Line Items]    
Net capital 4,800,000  
Excess net capital 4,500,000  
Cash and securities segregated for regulatory and other purposes 15,700,000  
Oppenheimer Europe [Member]
    
Schedule Of Compliance With Regulatory Capital Requirements Under Brokers And Dealers [Line Items]    
Net capital 4,200,000  
Excess net capital 800,000  
Regulatory capital required to be maintained 3,400,000  
Oppenheimer Investments Asia [Member]
    
Schedule Of Compliance With Regulatory Capital Requirements Under Brokers And Dealers [Line Items]    
Net capital 1,300,000  
Excess net capital 897,000  
Regulatory capital required to be maintained $ 387,000