Collateralized transactions - Narrative (Details)	3 Months Ended
Mar. 31, 2025 USD ($) customer dealer	Dec. 31, 2024 USD ($)
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Bank call loans	$ 359,500,000	$ 252,100,000
Market value of securities	23,100,000	377,600,000
Customer securities under customer margin loans that are available to be pledged	1,900,000,000
Re-pledged amounts under securities loans agreements	306,000,000
Customer securities directly with the Options Clearing Corporation to secure obligations and margin requirements under option contracts written by customers	294,100,000
Outstanding letters of credit	0
Amounts pledged	$ 1,178,324,000	1,015,604,000
Number of broker-dealers \| dealer	3
Receivable from brokers and clearing organizations	$ 77,300,000
Number of customers \| customer	2
Receivable from customers	$ 686,900,000
Number of business days for related transactions (in days)	1 day
2 Largest Customers \| Accounts Receivable \| Customer Concentration Risk
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Concentration risk, percentage	51.00%
Corporate equities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair value of securities received as collateral	$ 106,400,000	131,700,000
Corporate equities \| Reverse Repurchase Agreements
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair value of collateral	292,800,000	68,100,000
Corporate equities \| Securities Borrowed Transactions
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair value of securities received as collateral, sold and re-pledged under securities loaned	$ 43,700,000	39,200,000
Corporate equities \| Repurchase Agreements
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair value of collateral		$ 68,100,000

Credit Concentration, Receivable from Customer in Brokerage

No definition available.

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- Definition

Credit concentration receivable from major broker dealers.

+ References

No definition available.

+ Details

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- Definition

Customer Securities Pledged with the Options Clearing Corporation

+ References

No definition available.

+ Details

Name:	opy_CustomerSecuritiesDirectlyWithTheOptionsClearingCorporationToSecureObligationsAndMarginRequirementsUnderOptionContractsWrittenByCustomers
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- Definition

Customer Securities under Customer Margin Loans that are Available to be Pledged

+ References

No definition available.

+ Details

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Namespace Prefix:	opy_
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Period Type:	instant

- Definition

Customer Securities under Customer Margin Loans that are Available to be Pledged, Re-pledged Amount

+ References

No definition available.

+ Details

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Namespace Prefix:	opy_
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- Definition

Fair value of Securities Received as Collateral, Sold and Re-Pledged under Securities Loaned

+ References

No definition available.

+ Details

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- Definition

Fair Value Of Securities Received As Collateral Under Securities Borrowed Transactions

+ References

No definition available.

+ Details

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Namespace Prefix:	opy_
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- Definition

Firm's Securities Fair Value, Collateral for Bank Loans

+ References

No definition available.

+ Details

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Data Type:	xbrli:monetaryItemType
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Period Type:	instant

- Definition

Pledged securities owned and pledged as collateral amount eligible to be repledged by counterparty carrying value.

+ References

No definition available.

+ Details

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Namespace Prefix:	opy_
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Period Type:	instant

- Definition

Receivable from Customer in Brokerage, Number of Customers

+ References

No definition available.

+ Details

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Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant

- Definition

Receivables From Brokers-Dealers And Clearing Organizations, Number Of Major Broker-Dealers

+ References

No definition available.

+ Details

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Namespace Prefix:	opy_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant

- Definition

Transaction Settlement Period

+ References

No definition available.

+ Details

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

- Definition

Amount of short-term bank loan secured by broker-dealer customer's security.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Name Rule 15c3-1
-Number 240
-Section 15c3-1
-Publisher SEC

+ Details

Name:	srt_BankLoans
Namespace Prefix:	srt_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

For an entity that discloses a concentration risk in relation to quantitative amount, which serves as the "benchmark" (or denominator) in the equation, this concept represents the concentration percentage derived from the division.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 280
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 42
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482810/280-10-50-42

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Name Accounting Standards Codification
-Topic 825
-SubTopic 10
-Section 50
-Paragraph 21
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482907/825-10-50-21

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Name Accounting Standards Codification
-Topic 825
-SubTopic 10
-Section 50
-Paragraph 20
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482907/825-10-50-20

Reference 4: http://fasb.org/us-gaap/role/ref/legacyRef
-Name Accounting Standards Codification
-Topic 275
-SubTopic 10
-Section 50
-Paragraph 18
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482861/275-10-50-18

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-Name Accounting Standards Codification
-Topic 275
-SubTopic 10
-Section 50
-Paragraph 20
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482861/275-10-50-20

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Data Type:	dtr-types:percentItemType
Balance Type:	na
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- 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

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- Definition

The total amount of the contingent obligation under letters of credit outstanding as of the reporting date.

+ References

No definition available.

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Fair value of securities pledged as collateral against securities sold under agreement to repurchase.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 210
-SubTopic 20
-Name Accounting Standards Codification
-Section 55
-Paragraph 12
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147483444/210-20-55-12

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- Details

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- Details

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- Details

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- Details

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