FAIR VALUE - Consolidated Funds Summary of Valuation Techniques and Quantitative Information (Details) - Consolidated Funds $ in Thousands	9 Months Ended	12 Months Ended
	Sep. 30, 2017 USD ($)	Dec. 31, 2016 USD ($)
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Investments, at fair value	$ 5,195,525	$ 3,808,234
Level III
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Investments, at fair value	222,021	244,354
Level III | Credit-oriented investments: | Consumer discretionary | Discounted cash flow
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Investments, at fair value	$ 2,066	$ 7,658
Level III | Credit-oriented investments: | Consumer discretionary | Discounted cash flow | Minimum
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Discount rate	11.00%	5.00%
Level III | Credit-oriented investments: | Consumer discretionary | Discounted cash flow | Maximum
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Discount rate	19.00%	13.00%
Level III | Credit-oriented investments: | Consumer discretionary | Discounted cash flow | Weighted Average
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Discount rate	16.00%	7.00%
Level III | Credit-oriented investments: | Consumer discretionary | Recent market information
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Investments, at fair value	$ 52,487	$ 64,147
Level III | Credit-oriented investments: | Consumer staples | Discounted cash flow
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Investments, at fair value	$ 1,636	$ 7,356
Level III | Credit-oriented investments: | Consumer staples | Discounted cash flow | Minimum
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Discount rate	12.00%	6.00%
Level III | Credit-oriented investments: | Consumer staples | Discounted cash flow | Maximum
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Discount rate	14.00%	12.00%
Level III | Credit-oriented investments: | Consumer staples | Discounted cash flow | Weighted Average
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Discount rate	13.00%	7.00%
Level III | Credit-oriented investments: | Consumer staples | Recent market information
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Investments, at fair value	$ 12,607	$ 23,182
Level III | Credit-oriented investments: | Financials | Recent market information
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Investments, at fair value	30,148
Level III | Credit-oriented investments: | Financials | Recent transaction price
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Investments, at fair value	406
Level III | Credit-oriented investments: | Health care | Discounted cash flow
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Investments, at fair value	$ 9,314
Level III | Credit-oriented investments: | Health care | Discounted cash flow | Minimum
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Discount rate	8.00%
Level III | Credit-oriented investments: | Health care | Discounted cash flow | Maximum
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Discount rate	15.00%
Level III | Credit-oriented investments: | Health care | Discounted cash flow | Weighted Average
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Discount rate	11.00%
Level III | Credit-oriented investments: | Health care | Recent market information
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Investments, at fair value	$ 4,809
Level III | Credit-oriented investments: | Health care | Market approach (comparable companies)
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Investments, at fair value	$ 726
Level III | Credit-oriented investments: | Health care | Market approach (comparable companies) | Minimum
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Earnings multiple	9
Level III | Credit-oriented investments: | Health care | Market approach (comparable companies) | Maximum
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Earnings multiple	11
Level III | Credit-oriented investments: | Health care | Market approach (comparable companies) | Weighted Average
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Earnings multiple	10
Level III | Credit-oriented investments: | Energy | Recent market information
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Investments, at fair value		12,758
Level III | Credit-oriented investments: | Industrials | Discounted cash flow
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Investments, at fair value	$ 14,627	$ 10,574
Level III | Credit-oriented investments: | Industrials | Discounted cash flow | Minimum
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Discount rate	6.00%	5.00%
Level III | Credit-oriented investments: | Industrials | Discounted cash flow | Maximum
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Discount rate	11.00%	7.00%
Level III | Credit-oriented investments: | Industrials | Discounted cash flow | Weighted Average
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Discount rate	7.00%	6.00%
Level III | Credit-oriented investments: | Industrials | Recent market information
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Investments, at fair value	$ 19,362	$ 30,531
Level III | Credit-oriented investments: | Industrials | Market approach (comparable companies)
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Investments, at fair value	$ 4,210	$ 4,230
Level III | Credit-oriented investments: | Industrials | Market approach (comparable companies) | Minimum
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Earnings multiple	4	5
Level III | Credit-oriented investments: | Industrials | Market approach (comparable companies) | Maximum
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Earnings multiple	6	7
Level III | Credit-oriented investments: | Industrials | Market approach (comparable companies) | Weighted Average
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Earnings multiple	5	6
Level III | Credit-oriented investments: | Information technology | Discounted cash flow
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Investments, at fair value	$ 4,766	$ 11,681
Level III | Credit-oriented investments: | Information technology | Discounted cash flow | Minimum
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Discount rate	11.00%	6.00%
Level III | Credit-oriented investments: | Information technology | Discounted cash flow | Maximum
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Discount rate	12.00%	13.00%
Level III | Credit-oriented investments: | Information technology | Discounted cash flow | Weighted Average
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Discount rate	12.00%	9.00%
Level III | Credit-oriented investments: | Information technology | Recent market information
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Investments, at fair value	$ 8,780	$ 5,076
Level III | Credit-oriented investments: | Materials | Discounted cash flow
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Investments, at fair value		$ 1,206
Level III | Credit-oriented investments: | Materials | Discounted cash flow | Minimum
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Discount rate		11.00%
Level III | Credit-oriented investments: | Materials | Discounted cash flow | Maximum
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Discount rate		13.00%
Level III | Credit-oriented investments: | Materials | Discounted cash flow | Weighted Average
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Discount rate		12.00%
Level III | Credit-oriented investments: | Materials | Recent market information
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Investments, at fair value		$ 15,586
Level III | Credit-oriented investments: | Real estate | Discounted cash flow
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Investments, at fair value	$ 3,129
Level III | Credit-oriented investments: | Real estate | Discounted cash flow | Minimum
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Discount rate	11.00%
Level III | Credit-oriented investments: | Real estate | Discounted cash flow | Maximum
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Discount rate	13.00%
Level III | Credit-oriented investments: | Real estate | Discounted cash flow | Weighted Average
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Discount rate	12.00%
Level III | Credit-oriented investments: | Real estate | Recent market information
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Investments, at fair value	$ 18,120
Level III | Credit-oriented investments: | Real estate | Recent transaction price
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Investments, at fair value	335
Level III | Credit-oriented investments: | Other | Discounted cash flow
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Investments, at fair value	$ 4,284	$ 13,754
Level III | Credit-oriented investments: | Other | Discounted cash flow | Minimum
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Discount rate	10.00%	8.00%
Level III | Credit-oriented investments: | Other | Discounted cash flow | Maximum
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Discount rate	12.00%	16.00%
Level III | Credit-oriented investments: | Other | Discounted cash flow | Weighted Average
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Discount rate	11.00%	12.00%
Level III | Credit-oriented investments: | Other | Recent market information
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Investments, at fair value	$ 22,496	$ 9,137
Level III | Credit-oriented investments: | Other | Recent transaction price
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Investments, at fair value		20,785
Level III | Equity investments | Discounted cash flow
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Investments, at fair value	$ 1,323	$ 1,352
Level III | Equity investments | Discounted cash flow | Minimum
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Discount rate	11.00%	11.00%
Level III | Equity investments | Discounted cash flow | Maximum
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Discount rate	30.00%	33.00%
Level III | Equity investments | Discounted cash flow | Weighted Average
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Discount rate	13.00%	14.00%
Level III | Equity investments | Recent market information
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Investments, at fair value	$ 2,240	$ 1,799
Level III | Equity investments | Market approach (comparable companies)
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Investments, at fair value	$ 4,150	$ 3,542
Level III | Equity investments | Market approach (comparable companies) | Minimum
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Earnings multiple	4	4
Level III | Equity investments | Market approach (comparable companies) | Maximum
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Earnings multiple	11	11
Level III | Equity investments | Market approach (comparable companies) | Weighted Average
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Earnings multiple	7	8