COMMITMENTS AND CONTINGENCIES (Details) - USD ($)	3 Months Ended			9 Months Ended
	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Sep. 30, 2017	Dec. 31, 2016
COMMITMENTS AND CONTINGENCIES
Unfunded capital commitments	$ 316,500,000			$ 316,500,000	$ 535,300,000
Performance Fees
Performance Fees
Performance fees subject to potential clawback provision	471,800,000			471,800,000	418,300,000
Performance fees subject to potential claw back provision that are reimbursable by professionals	366,600,000			366,600,000	323,900,000
EIF Management, LLC
COMMITMENTS AND CONTINGENCIES
Unfunded commitment related to acquisition					20,300,000
Reverse in contingent consideration liability			$ 20,300,000
Kayne Anderson Capital Advisors L.P.
COMMITMENTS AND CONTINGENCIES
Unfunded capital commitments	20,000,000			20,000,000	$ 89,200,000
ARCC | American Capital Ltd.
ARCC and American Capital, Ltd. Merger Agreement
Maximum fees waived	10,000,000
Term of fee waiver		30 months
Maximum amount that shortfall will not carry over	10,000,000
Remaining fees waived	$ 80,000,000			$ 80,000,000
Remaining term of fee waiver				24 months