Collateralized transactions - Narrative (Details)	12 Months Ended
Dec. 31, 2024 USD ($) dealer customer	Dec. 31, 2023 USD ($)
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Bank call loans	$ 252,100,000	$ 0
Market value of securities	43,000,000	238,400,000
Customer securities under customer margin loans that are available to be pledged	1,900,000,000
Re-pledged amounts under securities loans agreements	187,500,000
Customer securities pledged directly with the Options Clearing Corporation to secure obligations	228,300,000
Letters of credit outstanding,	0
Amount pledged	$ 1,015,604,000	689,381,000
Number of broker-dealers \| dealer	3
Receivable from brokers and clearing organizations	$ 82,900,000
Number of customers \| customer	2
Receivable from customers	$ 666,100,000
Number of business days for related transactions (in days)	1 day
Accounts Receivable \| Customer Concentration Risk \| 2 Largest Customers
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Percentage of margin loans	52.00%
Equity Securities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair value of securities received as collateral	$ 131,700,000	151,900,000
Equity Securities \| Reverse Repurchase Agreements
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair value of collateral	68,100,000	8,800,000
Equity Securities \| 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	$ 39,200,000	61,500,000
Equity Securities \| Repurchase Agreements
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair value of collateral		$ 8,800,000

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 Directly With Options Clearing Corporation To Secure Obligations

+ References

No definition available.

+ Details

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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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- 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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- 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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- Definition

Firm's Securities Fair Value, Collateral for Bank Loans

+ References

No definition available.

+ Details

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Data Type:	xbrli:monetaryItemType
Balance Type:	debit
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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- 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_
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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

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-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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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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Data Type:	xbrli:monetaryItemType
Balance Type:	credit
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- 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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