INVESTMENTS, AT FAIR VALUE - Additional Information (Detail)	Mar. 31, 2013	Dec. 31, 2012
Investments [Abstract]
Percentage exceeded consolidated net assets	5.00%	5.00%

Individual issuer or investment threshold of fair value over companys net assets.

No definition available.

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