COMMITMENTS AND CONTINGENCIES (Details)		1 Months Ended	12 Months Ended
	Jan. 03, 2017 USD ($) item $ / shares	Jan. 31, 2015 USD ($)	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)	Jul. 30, 2014 USD ($)
COMMITMENTS AND CONTINGENCIES
Unfunded capital commitments			$ 535,300,000	$ 436,400,000
Future minimum commitments
2017			23,940,000
2018			25,615,000
2019			25,351,000
2020			21,333,000
2021			17,018,000
Thereafter			69,564,000
Total			182,821,000
Kayne Anderson Capital Advisors L.P.
COMMITMENTS AND CONTINGENCIES
Unfunded capital commitments			34,500,000
General, administrative and other expense
Operating Leases
Rent expense			26,400,000	18,500,000	$ 17,900,000
EIF Management, LLC
COMMITMENTS AND CONTINGENCIES
The fair value of the cash and equity portion		$ 59,200,000
Increase (decrease) in contingent consideration liability			17,800,000	21,100,000
Unfunded commitment related to acquisition			20,300,000	38,100,000
Contingent consideration			20,300,000	38,100,000
ARCC and American Capital, Ltd. Merger Agreement
Consideration transferred		149,171,000
Cash consideration		$ 64,532,000
ARCC | American Capital Ltd. | Subsequent event
ARCC and American Capital, Ltd. Merger Agreement
Consideration transferred	$ 4,200,000,000
Cash consideration	$ 275,000,000
Share price (USD per share) | $ / shares	$ 1.20
Maximum fees waived	$ 10,000,000
Term of fee waiver | item	10
ACRE | Guarantee Facility
Guarantees
Maximum borrowing capacity						$ 75,000,000.0
Performance Fees
Performance Fees
Performance fees subject to potential clawback provision			418,300,000	322,200,000
Performance fees subject to potential claw back provision that are reimbursable by professionals			$ 323,900,000	$ 247,900,000