Commitments and Contingencies Narrative (Details) $ in Millions	Sep. 30, 2019 USD ($)
Loss Contingencies [Line Items]
Auction Rate Securities Committed To Purchase related to settlements with regulators	$ 3.4
Auction Rate Securities Committed To Purchase as a Result of Legal Settlements and Awards	3.6
Minimum [Member]
Loss Contingencies [Line Items]
Loss Contingency, Range of Possible Loss, Portion Not Accrued	0.0
Maximum [Member]
Loss Contingencies [Line Items]
Loss Contingency, Range of Possible Loss, Portion Not Accrued	$ 3.0

Auction Rate Securities Committed To Purchase as a Result of Legal Settlements and Awards

No definition available.

Name:	opy_AuctionRateSecuritiesCommittedToPurchaseasaResultofLegalSettlementsandAwards
Namespace Prefix:	opy_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Auction Rate Securities Committed To Purchase related to settlements with regulators

+ References

No definition available.

+ Details

Name:	opy_AuctionRateSecuritiesCommittedToPurchaserelatedtosettlementswithregulators
Namespace Prefix:	opy_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

+ Details

Name:	us-gaap_LossContingenciesLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

The difference between the maximum amount of estimated loss and the amount recorded as of the balance sheet date.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 450
-SubTopic 20
-Section 05
-Paragraph 5
-URI http://asc.fasb.org/extlink&oid=99385795&loc=d3e12631-108344

+ Details

Name:	us-gaap_LossContingencyRangeOfPossibleLossPortionNotAccrued
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Details

Name:	srt_RangeAxis=srt_MinimumMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_RangeAxis=srt_MaximumMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: