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Financial Instruments - Investments in Company-Sponsored Funds (Parenthetical) (Detail) | 3 Months Ended
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Jun. 30, 2014
Private Equity Funds [Member] |
Investment Holdings [Line Items] |
Investments lock in period | 10 years
Maximum [Member] | Hedge Funds [Member] |
Investment Holdings [Line Items] |
Investments lock in period | 1 year

X
- Definition Investments lock in period. + References No definition available. + Details
Name: | opy_InvestmentsLockInPeriod
Namespace Prefix: | opy_
Data Type: | xbrli:durationItemType
Balance Type: | na
Period Type: | duration

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- Details
Name: | us-gaap_InvestmentHoldingsLineItems
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration