Regulatory requirements (Details) - USD ($)	3 Months Ended	6 Months Ended
Mar. 31, 2026	Jun. 30, 2026
Regulatory Capital Requirements [Line Items]
Regulatory capital required to be maintained		$ 4,150,000
Oppenheimer
Regulatory Capital Requirements [Line Items]
Required percentage of net capital to aggregate customer-related debit items (as a percent)		2.00%
Net capital		$ 444,800,000
Aggregate indebtedness (as a percent)		20.10%
Excess capital		$ 400,500,000
Freedom
Regulatory Capital Requirements [Line Items]
Aggregate indebtedness (as a percent)	6.67%
Oppenheimer Europe Ltd \| Basel Three New Requirements
Regulatory Capital Requirements [Line Items]
Common Equity Tier 1 ratio (as a percent)		139.00%
Common equity tier 1 ratio required (as a percent)		56.00%
Tier 1 capital ratio (as a percent)		139.00%
Tier 1 capital ratio required (as a percent)		75.00%
Total capital ratio (as a percent)		198.00%
Total capital ratio required (as a percent)		100.00%
Oppenheimer Investments Asia Ltd.
Regulatory Capital Requirements [Line Items]
Net capital		$ 3,300,000
Excess liquid capital under hong kong SFC rules		2,900,000
Regulatory capital required to be maintained		$ 383,000

Banking Regulation, Common Equity Tier One Ratio

No definition available.

Name:	opy_BankingRegulationCommonEquityTierOneRatio
Namespace Prefix:	opy_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Broker-Deal, Minimum Net Capital Requirement, Parent

+ References

No definition available.

+ Details

Name:	opy_BrokerDealMinimumNetCapitalRequirementParent
Namespace Prefix:	opy_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Common Equity Tier One Ratio required for capital adequacy purposes under the Capital Requirements Directive (DRD IV) in the European Union.

+ References

No definition available.

+ Details

Name:	opy_CommonEquityTierOneRatioRequiredUnderCrdFourth
Namespace Prefix:	opy_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Excess Liquid Capital Under Hong Kong SFC Rules

+ References

No definition available.

+ Details

Name:	opy_ExcessLiquidCapitalUnderHongKongSFCRules
Namespace Prefix:	opy_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Liquid Capital Under Hong Kong SFC Rules

+ References

No definition available.

+ Details

Name:	opy_LiquidCapitalUnderHongKongSFCRules
Namespace Prefix:	opy_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Percentage of net capital to aggregate indebtedness.

+ References

No definition available.

+ Details

Name:	opy_PercentageOfNetCapitalToAggregateIndebtedness
Namespace Prefix:	opy_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Tier One Capital Ratio calculated for capital adequacy purposes under the Capital Requirements Directive (DRD IV) in the European Union.

+ References

No definition available.

+ Details

Name:	opy_TierOneCapitalRatioCalculatedUnderCrdFourth
Namespace Prefix:	opy_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Tier One Capital Ratio required for capital adequacy purposes under the Capital Requirements Directive (DRD IV) in the European Union.

+ References

No definition available.

+ Details

Name:	opy_TierOneCapitalRatioRequiredUnderCrdFourth
Namespace Prefix:	opy_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Total Capital Ratio calculated for capital adequacy purposes under the Capital Requirements Directive (DRD IV) in the European Union.

+ References

No definition available.

+ Details

Name:	opy_TotalCapitalRatioCalculatedUnderCrdFourth
Namespace Prefix:	opy_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Total Capital Ratio Required for capital adequacy purposes under the Capital Requirements Directive (DRD IV) in the European Union.

+ References

No definition available.

+ Details

Name:	opy_TotalCapitalRatioRequiredUnderCrdFourth
Namespace Prefix:	opy_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Amount of net capital in excess of minimum required net capital, calculated under Alternative Standard.

+ References

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

+ Details

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

- Definition

Minimum amount of net capital required to be maintained by broker-dealer and its subsidiary, calculated under Aggregate Indebtedness Standard.

+ References

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

+ Details

Name:	srt_MinimumNetCapitalRequired1
Namespace Prefix:	srt_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Amount of net capital of broker-dealer.

+ References

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

+ Details

Name:	srt_NetCapital
Namespace Prefix:	srt_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
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

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 942
-SubTopic 505
-Name Accounting Standards Codification
-Section 50
-Paragraph 1B
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147477270/942-505-50-1B

Reference 2: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 942
-SubTopic 505
-Name Accounting Standards Codification
-Section 50
-Paragraph 1
-Subparagraph (c)(1)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147477270/942-505-50-1

+ Details

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

- Details

Name:	us-gaap_RegulatoryLiabilityAxis=opy_OppenheimerMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_RegulatoryLiabilityAxis=opy_FreedomMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_RegulatoryLiabilityAxis=opy_OppenheimerEuropeMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	opy_RegulatoryCapitalRequirementAxis=opy_BaselThreeNewRequirementsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_RegulatoryLiabilityAxis=opy_OppenheimerInvestmentsAsiaMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: