INVESTMENTS - Net Gains (Losses) from Investment Activities of Consolidated Funds (Details) - USD ($) $ in Thousands	3 Months Ended	6 Months Ended
Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Gain (Loss) on Securities [Line Items]
Net realized gain (loss) on consolidated funds’ investments	$ 447	$ (17,296)	$ (5,372)	$ (2,697)
Net change in unrealized appreciation (depreciation) on consolidated funds’ investments	1,814	(31,105)	58,931	(45,491)
Consolidated Funds \| Not Designated as Hedging Instrument
Gain (Loss) on Securities [Line Items]
Net realized gain (loss) on consolidated funds’ investments	447	(17,296)	(5,372)	(2,697)
Net change in unrealized appreciation (depreciation) on consolidated funds’ investments	1,814	(31,105)	58,931	(45,491)
Consolidated Funds \| Investments and other financial instruments \| Not Designated as Hedging Instrument
Gain (Loss) on Securities [Line Items]
Net realized gain (loss) on consolidated funds’ investments	233	(13,856)	(7,712)	(2,534)
Net change in unrealized appreciation (depreciation) on consolidated funds’ investments	22,562	(46,500)	152,232	(77,088)
Consolidated Funds \| CLO Liabilities \| Not Designated as Hedging Instrument
Gain (Loss) on Securities [Line Items]
Net realized gain (loss) on consolidated funds’ investments	0	0	0	0
Net change in unrealized appreciation (depreciation) on consolidated funds’ investments	(21,906)	14,785	(93,989)	32,857
Consolidated Funds \| Foreign-currency forward contracts \| Not Designated as Hedging Instrument
Gain (Loss) on Securities [Line Items]
Net Realized Gain (Loss) on Investments	214	(2,507)	2,340	(1,068)
Net Change in Unrealized Appreciation (Depreciation) on Investments	1,158	(465)	688	(1,176)
Consolidated Funds \| Total-return and interest-rate swaps \| Not Designated as Hedging Instrument
Gain (Loss) on Securities [Line Items]
Net Realized Gain (Loss) on Investments	0	838	0	858
Net Change in Unrealized Appreciation (Depreciation) on Investments	0	115	0	29
Consolidated Funds \| Options and futures \| Not Designated as Hedging Instrument
Gain (Loss) on Securities [Line Items]
Net Realized Gain (Loss) on Investments	0	(1,771)	0	47
Net Change in Unrealized Appreciation (Depreciation) on Investments	$ 0	$ 960	$ 0	$ (113)

Amount of increase (decrease) in the fair value of derivatives recognized in the income statement.

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 4A
-Subparagraph (b)(1)
-URI http://asc.fasb.org/extlink&oid=109980867&loc=SL5618551-113959

+ Details

Name:	us-gaap_DerivativeGainLossOnDerivativeNet
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

The net realized gains or losses on investments during the period, not including gains or losses on securities separately or otherwise categorized as trading, available-for-sale, or held-to-maturity.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 220
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-04.3(a))
-URI http://asc.fasb.org/extlink&oid=116637232&loc=SL114874131-224263

+ Details

Name:	us-gaap_RealizedInvestmentGainsLosses
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
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_ScheduleOfGainLossOnInvestmentsIncludingMarketableSecuritiesAndInvestmentsHeldAtCostIncomeStatementReportedAmountsSummaryLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

The net change in the difference between the fair value and the carrying value, or in the comparative fair values, of derivative instruments, including options, swaps, futures, and forward contracts, held at each balance sheet date, that was included in earnings for the period.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 28
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=118932676&loc=d3e3602-108585

+ Details

Name:	us-gaap_UnrealizedGainLossOnDerivatives
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

The net change in the difference between the fair value and the carrying value, or in the comparative fair values, of investments, not including unrealized gains or losses on securities separately or otherwise categorized as trading, available-for-sale, or held-to-maturity, held at each balance sheet date and included in earnings for the period.

+ References

+ Details

Name:	us-gaap_UnrealizedGainLossOnInvestments
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Details

Name:	us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis=us-gaap_VariableInterestEntityPrimaryBeneficiaryAggregatedDisclosureMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_HedgingDesignationAxis=us-gaap_NondesignatedMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DerivativeInstrumentRiskAxis=oak_InvestmentsAndOtherFinancialInstrumentsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DerivativeInstrumentRiskAxis=oak_MeasurementAlternativeGuidanceForCLOsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DerivativeInstrumentRiskAxis=oak_ForeignCurrencyForwardContractMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DerivativeInstrumentRiskAxis=oak_TotalReturnCreditDefaultAndInterestRateSwapsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DerivativeInstrumentRiskAxis=oak_OptionsAndFuturesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: