COMMITMENTS AND CONTINGENCIES (Details) - USD ($)	3 Months Ended
	Mar. 31, 2017	Dec. 31, 2016
COMMITMENTS AND CONTINGENCIES
Unfunded capital commitments	$ 527,100,000	$ 535,300,000
Kayne Anderson Capital Advisors L.P.
COMMITMENTS AND CONTINGENCIES
Unfunded capital commitments	35,100,000	89,200,000
EIF Management, LLC
COMMITMENTS AND CONTINGENCIES
Unfunded commitment related to acquisition		20,300,000
Increase (decrease) in contingent consideration liability	20,300,000
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
Performance Fees
Performance Fees
Performance fees subject to potential clawback provision	419,100,000	418,300,000
Performance fees subject to potential claw back provision that are reimbursable by professionals	$ 324,300,000	$ 323,900,000