SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Details)	12 Months Ended
	Dec. 31, 2017 USD ($) entity	Dec. 31, 2016 USD ($) entity	Dec. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)
Equity Appropriated for Consolidated Funds
Number of CLOs consolidated | entity	10	7
Cumulative effect of accounting change			$ (3,367,000)	$ (4,625,837,000)
Fees
Carried interest, contingent repayment obligations	$ 0	$ 0
Performance Fees
Performance fee compensation, employment or service period	5 years
Foreign Currency
Foreign currency transaction gain (loss)	$ (1,700,000)	$ 16,200,000	(300,000)
ARCC
Fees
Management fees as a percentage of net investment income	20.00%
Hurdle rate per quarter (as a percent)	1.75%
Hurdle rate per annum (as a percent)	7.00%
Percentage of net investment income received from first dollar earned	20.00%
Minimum
Goodwill and Intangible Assets
Estimated useful lives, intangible assets	3 years 6 months
Minimum | Property, Plant and Equipment Other Than Leasehold Improvements and Internal Use Software [Member]
Fixed Assets
Estimated useful life	3 years
Maximum
Goodwill and Intangible Assets
Estimated useful lives, intangible assets	13 years 6 months
Maximum | Property, Plant and Equipment Other Than Leasehold Improvements and Internal Use Software [Member]
Fixed Assets
Estimated useful life	7 years
Accounting Standards Update 2014-13
Equity Appropriated for Consolidated Funds
Cumulative effect of accounting change			$ 3,400,000