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Earnings Per Share - Summary of Earnings Per Share (Narrative) (Details)
 12 Months Ended
Dec. 31, 2014
Dec. 31, 2013
Dec. 31, 2012
Class A Stock      
Schedule Of Earnings Per Share Basic And Diluted [Line Items]      
Number of anti-dilutive warrants, options and restricted shares, for the year 43,008us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount
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= us-gaap_CommonClassAMember		 57,573us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount
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= us-gaap_CommonClassAMember		 1,936,871us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount
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CIBC World Markets Corp. | January 2008 Acquisition      
Schedule Of Earnings Per Share Basic And Diluted [Line Items]      
Period for exercise of warrant 5 years    
Acquisition date of CIBC World Markets Corp. Jan. 14, 2008    
Warrants expire date 2013-04-13    
CIBC World Markets Corp. | January 2008 Acquisition | Class A Stock      
Schedule Of Earnings Per Share Basic And Diluted [Line Items]      
Company issued a warrant to purchase share of Class A Stock 1,000,000us-gaap_ClassOfWarrantOrRightNumberOfSecuritiesCalledByWarrantsOrRights
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= us-gaap_CommonClassAMember		    
Class A Stock exercisable 48.62us-gaap_ClassOfWarrantOrRightExercisePriceOfWarrantsOrRights
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= opy_JanuaryTwoThousandEightAcquisitionMember
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