Fair value measurements - Narrative (Details) - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2023	Dec. 31, 2022
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Securities owned, at fair value	$ 795,312	$ 498,594
Auction rate securities valuation adjustment	200
Investments	$ 18,785	7,068
Forward or delayed delivery of the underlying instrument with settlement	180 days
Level 2
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Securities owned, at fair value	$ 64,683	79,166
Investments	16,913	$ 7,068
Level 2 \| Other Assets
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Investments	$ 7,100

Auction Rate Securities Valuation Adjustment

No definition available.

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

- Definition

Maximum settlement period in case of delayed delivery of underlying instrument.

+ References

No definition available.

+ Details

Name:	opy_MaximumSettlementPeriodInCaseOfDelayedDeliveryOfUnderlyingInstrument
Namespace Prefix:	opy_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

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

- Definition

Sum of the carrying amounts as of the balance sheet date of all investments.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 944
-SubTopic 210
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-03(a)(1)(h))
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147479440/944-210-S99-1

+ Details

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

- Definition

Fair value of financial instruments held by a broker-dealer for their own account (proprietary securities) for trading or investment purposes determined by management based upon quoted prices of a financial instrument with similar characteristics or on a valuation technique or model.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Name Accounting Standards Codification
-Topic 940
-SubTopic 320
-Section 45
-Paragraph 2
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481961/940-320-45-2

+ Details

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

- Details

Name:	us-gaap_FairValueByFairValueHierarchyLevelAxis=us-gaap_FairValueInputsLevel2Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_BalanceSheetLocationAxis=us-gaap_OtherAssetsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: