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SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Incentive Income) (Details)	12 Months Ended
	Dec. 31, 2014
Accounting Policies [Abstract]
Incentive income, closed-end funds (as a percent)	20.00%oak_IncentiveIncomeClosedEndFunds
Preferred return, closed-end funds (as a percent)	8.00%oak_PreferredReturnClosedEndFunds
Incentive income, evergreen funds (as a percent)	20.00%oak_IncentiveIncomeEvergreenFunds