Deferred compensation arrangement amount of bonus awarded.

No definition available.

Name:	opy_DeferredCompensationArrangementAmountOfBonusAwarded
Namespace Prefix:	opy_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Deferred compensation vesting life.

+ References

No definition available.

+ Details

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

- Definition

Aggregate unrecognized cost of option awards made to employees under a stock appreciation rights plan or plans, that have yet to vest.

+ References

No definition available.

+ Details

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

- Definition

Liability Percentage offset by Company Owned Life Insurance

+ References

No definition available.

+ Details

Name:	opy_LiabilityPercentageoffsetbyCompanyOwnedLifeInsurance
Namespace Prefix:	opy_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Liability related to the OARs.

+ References

No definition available.

+ Details

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

- Definition

Number of stock appreciation rights granted.

+ References

No definition available.

+ Details

Name:	opy_NumberOfStockAppreciationRightsGranted
Namespace Prefix:	opy_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	duration

- Definition

Number of type of employee compensation plans granted under share-based compensation and cash-based compensation plans

+ References

No definition available.

+ Details

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

- Definition

Amount of difference between fair value and exercise price of outstanding and expected to vest stock appreciation rights.

+ References

No definition available.

+ Details

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

- Definition

Represents the expense recognized during the period arising from equity-based compensation arrangements (for example, shares of stock, unit, stock options or other equity instruments) with employees, directors and certain consultants qualifying for treatment as employees.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SAB Topic 14.F)
-URI http://asc.fasb.org/extlink&oid=27013229&loc=d3e301413-122809

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 1
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=96867065&loc=d3e5047-113901

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (h)(1)(i)
-URI http://asc.fasb.org/extlink&oid=96867065&loc=d3e5070-113901

+ Details

Name:	us-gaap_AllocatedShareBasedCompensationExpense
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

The compensation expense recognized during the period pertaining to the deferred compensation arrangement.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 1
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=96867065&loc=d3e5047-113901

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 710
-SubTopic 10
-Section 30
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=6409875&loc=d3e20015-108363

+ Details

Name:	us-gaap_DeferredCompensationArrangementWithIndividualCompensationExpense
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Aggregate carrying value as of the balance sheet date of the liabilities for all deferred compensation arrangements. Represents currently earned compensation under compensation arrangements that is not actually paid until a later date.

+ References

No definition available.

+ Details

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

- Definition

Amount of discretionary contributions made by an employer to a defined contribution plan.

+ References

No definition available.

+ Details

Name:	us-gaap_DefinedContributionPlanEmployerDiscretionaryContributionAmount
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Maximum amount the employee may contribute to a defined contribution plan.

+ References

No definition available.

+ Details

Name:	us-gaap_DefinedContributionPlanMaximumAnnualContributionsPerEmployeeAmount
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Weighted average period over which unrecognized compensation is expected to be recognized for equity-based compensation plans, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

+ References

+ Details

Name:	us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedPeriodForRecognition1
Namespace Prefix:	us-gaap_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Unrecognized cost of unvested share-based awards, other than options, awarded to employees as compensation.

+ References

+ Details

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

- Definition

Period which an employee's right to exercise an award is no longer contingent on satisfaction of either a service condition, market condition or a performance condition, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

+ References

+ Details

Name:	us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardVestingPeriod1
Namespace Prefix:	us-gaap_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

The number of grants made during the period on other than stock (or unit) option plans (for example, phantom stock or unit plan, stock or unit appreciation rights plan, performance target plan).

+ References

+ Details

Name:	us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod
Namespace Prefix:	us-gaap_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	duration

- Definition

The number of equity-based payment instruments, excluding stock (or unit) options, that vested during the reporting period.

+ References

+ Details

Name:	us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriod
Namespace Prefix:	us-gaap_
Data Type:	xbrli:sharesItemType
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_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

The difference between the maximum number of shares (or other type of equity) authorized for issuance under the plan (including the effects of amendments and adjustments), and the sum of: 1) the number of shares (or other type of equity) already issued upon exercise of options or other equity-based awards under the plan; and 2) shares (or other type of equity) reserved for issuance on granting of outstanding awards, net of cancellations and forfeitures, if applicable.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=96867065&loc=d3e5070-113901

+ Details

Name:	us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrant
Namespace Prefix:	us-gaap_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	instant

- Definition

Gross number of share options (or share units) granted during the period.

+ References

No definition available.

+ Details

Name:	us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodGross
Namespace Prefix:	us-gaap_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	duration

- Definition

Percentage of vesting of share-based compensation awards.

+ References

+ Details

Name:	us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardAwardVestingRightsPercentage
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Intrinsic value of equity-based compensation awards not vested. Excludes stock and unit options.

+ References

No definition available.

+ Details

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

- Definition

Period from grant date that an equity-based award expires, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

+ References

+ Details

Name:	us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardExpirationPeriod
Namespace Prefix:	us-gaap_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Expected term of share-based compensation awards, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (f)(2)(i)
-URI http://asc.fasb.org/extlink&oid=96867065&loc=d3e5070-113901

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SAB Topic 14.D.2)
-URI http://asc.fasb.org/extlink&oid=27013229&loc=d3e301413-122809

+ Details

Name:	us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardFairValueAssumptionsExpectedTerm1
Namespace Prefix:	us-gaap_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Details

Name:	us-gaap_StatementClassOfStockAxis=us-gaap_CommonClassAMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_AwardTypeAxis=us-gaap_RestrictedStockMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_AwardTypeAxis=us-gaap_EmployeeStockOptionMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_SubsequentEventTypeAxis=us-gaap_SubsequentEventMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_AwardTypeAxis=us-gaap_StockAppreciationRightsSARSMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_PlanNameAxis=opy_EmployeeSharePlanMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_RangeAxis=us-gaap_MinimumMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_RangeAxis=us-gaap_MaximumMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_PlanNameAxis=opy_OppenheimerHoldingsInc.StockAppreciationRightPlanMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_AwardTypeAxis=opy_StockAppreciationRightsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_PlanNameAxis=opy_EquityIncentivePlanMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_VestingAxis=opy_SecondAnniversaryMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_VestingAxis=opy_ThirdAnniversaryMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_VestingAxis=opy_FourthAnniversaryMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_VestingAxis=opy_ExpirationDateOneMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_PlanNameAxis=opy_StockIncentivePlanTwoThousandFourteenMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_TitleOfIndividualAxis=us-gaap_ExecutiveOfficerMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_TitleOfIndividualAxis=opy_NonEmployeeDirectorMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_VestingAxis=opy_FifthAnniversaryMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_PlanNameAxis=opy_ExecutiveDeferredCompensationPlanAndDeferredIncentivePlanMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_PlanNameAxis=opy_DeferredCompensationPlanMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Employee Compensation Plans - Additional Information (Narrative) (Details)					12 Months Ended
	Mar. 01, 2018 shares	Jan. 31, 2018 shares	Jan. 30, 2018 shares	Jan. 05, 2018 shares	Dec. 31, 2017 USD ($) employee_compensation_plan shares	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of Employee Compensation Plans Granted \| employee_compensation_plan					2
Maximum annual contribution under Defined Contribution Plan					$ 18,000	$ 18,000	$ 18,000,000,000
Employer contribution to Defined Contribution Plan					1,500,000	1,300,000	1,600,000
Deferred bonus amounts					$ 8,200,000	7,700,000	8,300,000
Vesting period of deferred bonus					5 years
Deferred compensation plans cost					$ 17,100,000	11,800,000	8,600,000
Class A Stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares of Class A Stock available \| shares					1,143,598
Restricted Stock \| Class A Stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Aggregate intrinsic value of ESP awards outstanding					$ 28,600,000
Compensation expense relating to the share-based awards					5,600,000	5,200,000	4,600,000
Unrecognized compensation cost related to unvested share-based compensation					$ 9,800,000
Cost is expected to be recognized over a weighted average period					2 years 2 months 24 days
Granted, Number of shares \| shares					464,100
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Vested in Period \| shares					548,062
Employee Stock Option
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Compensation expense relating to the share-based awards					$ 25,700	19,900	69,900
Employee Stock Option \| Subsequent Event [Member] \| Class A Stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period under share based payment			4 years 6 months
Number of Options, Granted \| shares			4,050
Stock Appreciation Rights (SARs) [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Compensation expense relating to the share-based awards					$ 6,900,000	$ 1,000,000	$ 1,800,000
Cost is expected to be recognized over a weighted average period					2 years 2 months
Aggregate intrinsic value of OARs outstanding and expected to vest					$ 15,000,000
Liability related to the OARs					7,100,000
Total unrecognized compensation cost					$ 8,300,000
Stock Appreciation Rights (SARs) [Member] \| Subsequent Event [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period under share based payment				5 years
Number Of Stock Appreciation Rights Granted \| shares				497,430
Employee Share Plan \| Minimum [Member] \| Class A Stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period under share based payment					3 years
Employee Share Plan \| Maximum [Member] \| Class A Stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period under share based payment					5 years
Oppenheimer Holdings Inc. Stock Appreciation Right Plan \| Stock Appreciation Rights [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period under share based payment					5 years
Equity Incentive Plan \| Class A Stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Term granted for options					5 years
Share-based Compensation Arrangement by Share-based Payment Award, Expiration Period					6 months
Equity Incentive Plan \| Second Anniversary \| Class A Stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting percentage under share based payment					25.00%
Equity Incentive Plan \| Third Anniversary \| Class A Stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting percentage under share based payment					25.00%
Equity Incentive Plan \| Fourth Anniversary \| Class A Stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting percentage under share based payment					25.00%
Equity Incentive Plan \| Six Months Before Expiration \| Class A Stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting percentage under share based payment					25.00%
Stock Incentive Plan 2014 \| Subsequent Event [Member] \| Class A Stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Granted, Number of shares \| shares			281,919
Stock Incentive Plan 2014 \| Subsequent Event [Member] \| Class A Stock \| Executive Officer [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period under share based payment		5 years
Granted, Number of shares \| shares		9,100
Stock Incentive Plan 2014 \| Subsequent Event [Member] \| Class A Stock \| Non Employee Director
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting percentage under share based payment	25.00%
Granted, Number of shares \| shares	17,500
Stock Incentive Plan 2014 \| Minimum [Member] \| Class A Stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period under share based payment					3 years
Stock Incentive Plan 2014 \| Maximum [Member] \| Class A Stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period under share based payment					5 years
Stock Incentive Plan 2014 \| Third Anniversary \| Subsequent Event [Member] \| Class A Stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period under share based payment			3 years
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Vested in Period \| shares			126,240
Stock Incentive Plan 2014 \| Fifth Anniversary [Domain] \| Subsequent Event [Member] \| Class A Stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period under share based payment			5 years
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Vested in Period \| shares			155,679
Executive Deferred Compensation Plan and Deferred Incentive Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Liability Percentage offset by Company Owned Life Insurance					60.00%
Company's deferred compensation liability					$ 52,300,000
CIBC Deferred Compensation Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Company's deferred compensation liability					$ 17,200,000