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Financial Instruments - Quantitative Information about Level 3 Fair Value Measurements (Parenthetical) (Detail) | Sep. 30, 2014
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Auction Rate Preferred Securities [Member] |
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items] |
U.S. Treasury rate | 1.40%
Municipal Securities [Member] |
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items] |
Fair value assumption discount rate range of spread rate on treasury securities | 175.00%
U.S. Treasury rate | 1.58%
Student Loan Auction Rate Securities [Member] |
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items] |
Fair value assumption discount rate range of spread rate on treasury securities | 1.20%
U.S. Treasury rate | 2.20%
Minimum [Member] | Auction Rate Preferred Securities [Member] |
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items] |
Fair value assumption discount rate range of spread rate on treasury securities | 110.00%
Maximum [Member] | Auction Rate Preferred Securities [Member] |
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items] |
Fair value assumption discount rate range of spread rate on treasury securities | 150.00%

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- Definition Spread represents ARS maximum formula which is used to discount for the lack of liquidity as a result of ARS failed auction. + References No definition available. + Details
Name: | opy_SpreadToUSTreasuryRate
Namespace Prefix: | opy_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | instant

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- Definition Specific period of US Treasury rate as of reporting period. + References No definition available. + Details
Name: | opy_USTreasuryRate
Namespace Prefix: | opy_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | instant

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