INVESTMENTS - Additional Information (Detail) - issuer	Jun. 30, 2016	Dec. 31, 2015
Schedule of Equity Method Investments [Line Items]
Number of issuers	0	0
Percentage exceeded consolidated net assets (as a percent)	5.00%	5.00%
Maximum
Schedule of Equity Method Investments [Line Items]
Ownership percentage	2.50%
DoubleLine
Schedule of Equity Method Investments [Line Items]
Ownership percentage	20.00%

Individual issuer or investment threshold of fair value over company's net assets.

No definition available.

Name:	oak_IndividualIssuerOrInvestmentThresholdOfFairValueOverCompanysNetAssetsPercentage
Namespace Prefix:	oak_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Number of Individual Issuers Exceeding Investment Threshold of Fair Value Over Company's Net Assets.

+ References

No definition available.

+ Details

Name:	oak_NumberofIndividualIssuersExceedingInvestmentThresholdofFairValueOverCompanysNetAssets.
Namespace Prefix:	oak_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant

- Definition

The percentage of ownership of common stock or equity participation in the investee accounted for under the equity method of accounting.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 323
-SubTopic 10
-Section 50
-Paragraph 3
-Subparagraph (a)(1)
-URI http://asc.fasb.org/extlink&oid=66011266&loc=d3e33918-111571

+ Details

Name:	us-gaap_EquityMethodInvestmentOwnershipPercentage
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
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

No definition available.

+ Details

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

- Details

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

- Details

Name:	invest_InvestmentAxis=oak_DoubleLineMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: