FAIR VALUE OF FINANCIAL INSTRUMENTS (Details 2) - USD ($) $ in Thousands	Jun. 30, 2017	Dec. 31, 2016
Assets:
Corporate debt securities	$ 263,055	$ 229,206
Total securities	263,055	229,206
Corporate loans	3,635,589	3,305,264
Equity investments, at estimated fair value	444,373	168,658
Interests in joint ventures and partnerships, at estimated fair value	1,009,737	793,996
Derivatives:
Total derivative assets	23,876	46,447
Liabilities:
Collateralized loan obligation secured notes, at estimated fair value	2,916,680	3,087,941
Derivatives:
Total derivative liabilities	33,277	32,705
Recurring basis | Estimated Fair Value
Assets:
Total securities	263,055	229,206
Corporate loans	3,635,589	3,305,264
Equity investments, at estimated fair value	444,373	168,658
Interests in joint ventures and partnerships, at estimated fair value	1,009,737	793,996
Derivatives:
Total derivative assets	23,876	46,447
Total	5,376,630	4,543,571
Derivatives:
Total derivative liabilities	33,277	32,705
Total	3,038,372	3,210,253
Recurring basis | Estimated Fair Value | Unaffiliated Entity
Liabilities:
Collateralized loan obligation secured notes, at estimated fair value	2,916,680	3,087,941
Recurring basis | Estimated Fair Value | Affiliated Entity
Liabilities:
Collateralized loan obligation secured notes, at estimated fair value	88,415	89,607
Recurring basis | Estimated Fair Value | Corporate Debt Securities
Assets:
Corporate debt securities	236,943	188,543
Recurring basis | Estimated Fair Value | Residential Mortgage- Backed Securities
Assets:
Residential mortgage-backed securities	26,112	40,663
Recurring basis | Estimated Fair Value | Foreign exchange forward contracts and options
Derivatives:
Derivative assets	20,494	43,918
Derivatives:
Derivative liabilities	5,007	5,442
Recurring basis | Estimated Fair Value | Warrants
Derivatives:
Derivative assets	1,795	1,528
Recurring basis | Estimated Fair Value | Options
Derivatives:
Derivative assets	1,587	1,001
Recurring basis | Estimated Fair Value | Interest rate swaps
Derivatives:
Derivative liabilities	28,270	27,263
Recurring basis | Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets:
Total securities	0	0
Corporate loans	0	0
Equity investments, at estimated fair value	53,562	36,353
Interests in joint ventures and partnerships, at estimated fair value	0	0
Derivatives:
Total derivative assets	0	0
Total	53,562	36,353
Derivatives:
Total derivative liabilities	0	0
Total	0	0
Recurring basis | Quoted Prices in Active Markets for Identical Assets (Level 1) | Unaffiliated Entity
Liabilities:
Collateralized loan obligation secured notes, at estimated fair value	0	0
Recurring basis | Quoted Prices in Active Markets for Identical Assets (Level 1) | Affiliated Entity
Liabilities:
Collateralized loan obligation secured notes, at estimated fair value	0	0
Recurring basis | Quoted Prices in Active Markets for Identical Assets (Level 1) | Corporate Debt Securities
Assets:
Corporate debt securities	0	0
Recurring basis | Quoted Prices in Active Markets for Identical Assets (Level 1) | Residential Mortgage- Backed Securities
Assets:
Residential mortgage-backed securities	0	0
Recurring basis | Quoted Prices in Active Markets for Identical Assets (Level 1) | Foreign exchange forward contracts and options
Derivatives:
Derivative assets	0	0
Derivatives:
Derivative liabilities	0	0
Recurring basis | Quoted Prices in Active Markets for Identical Assets (Level 1) | Warrants
Derivatives:
Derivative assets	0	0
Recurring basis | Quoted Prices in Active Markets for Identical Assets (Level 1) | Options
Derivatives:
Derivative assets	0	0
Recurring basis | Quoted Prices in Active Markets for Identical Assets (Level 1) | Interest rate swaps
Derivatives:
Derivative liabilities	0	0
Recurring basis | Significant Other Observable Inputs (Level 2)
Assets:
Total securities	3,983	13,337
Corporate loans	3,526,184	3,176,070
Equity investments, at estimated fair value	0	0
Interests in joint ventures and partnerships, at estimated fair value	0	0
Derivatives:
Total derivative assets	19,874	41,636
Total	3,550,041	3,231,043
Derivatives:
Total derivative liabilities	33,264	31,415
Total	3,038,359	3,208,963
Recurring basis | Significant Other Observable Inputs (Level 2) | Unaffiliated Entity
Liabilities:
Collateralized loan obligation secured notes, at estimated fair value	2,916,680	3,087,941
Recurring basis | Significant Other Observable Inputs (Level 2) | Affiliated Entity
Liabilities:
Collateralized loan obligation secured notes, at estimated fair value	88,415	89,607
Recurring basis | Significant Other Observable Inputs (Level 2) | Corporate Debt Securities
Assets:
Corporate debt securities	3,983	13,337
Recurring basis | Significant Other Observable Inputs (Level 2) | Residential Mortgage- Backed Securities
Assets:
Residential mortgage-backed securities	0	0
Recurring basis | Significant Other Observable Inputs (Level 2) | Foreign exchange forward contracts and options
Derivatives:
Derivative assets	19,874	41,636
Derivatives:
Derivative liabilities	4,994	4,152
Recurring basis | Significant Other Observable Inputs (Level 2) | Warrants
Derivatives:
Derivative assets	0	0
Recurring basis | Significant Other Observable Inputs (Level 2) | Options
Derivatives:
Derivative assets	0	0
Recurring basis | Significant Other Observable Inputs (Level 2) | Interest rate swaps
Derivatives:
Derivative liabilities	28,270	27,263
Recurring basis | Significant Unobservable Inputs (Level 3)
Assets:
Total securities	259,072	215,869
Corporate loans	109,405	129,194
Equity investments, at estimated fair value	390,811	132,305
Interests in joint ventures and partnerships, at estimated fair value	1,009,737	793,996
Derivatives:
Total derivative assets	4,002	4,811
Total	1,773,027	1,276,175
Derivatives:
Total derivative liabilities	13	1,290
Total	13	1,290
Recurring basis | Significant Unobservable Inputs (Level 3) | Unaffiliated Entity
Liabilities:
Collateralized loan obligation secured notes, at estimated fair value	0	0
Recurring basis | Significant Unobservable Inputs (Level 3) | Affiliated Entity
Liabilities:
Collateralized loan obligation secured notes, at estimated fair value	0	0
Recurring basis | Significant Unobservable Inputs (Level 3) | Corporate Debt Securities
Assets:
Corporate debt securities	232,960	175,206
Recurring basis | Significant Unobservable Inputs (Level 3) | Residential Mortgage- Backed Securities
Assets:
Residential mortgage-backed securities	26,112	40,663
Recurring basis | Significant Unobservable Inputs (Level 3) | Foreign exchange forward contracts and options
Derivatives:
Derivative assets	620	2,282
Derivatives:
Derivative liabilities	13	1,290
Recurring basis | Significant Unobservable Inputs (Level 3) | Warrants
Derivatives:
Derivative assets	1,795	1,528
Recurring basis | Significant Unobservable Inputs (Level 3) | Options
Derivatives:
Derivative assets	1,587	1,001
Recurring basis | Significant Unobservable Inputs (Level 3) | Interest rate swaps
Derivatives:
Derivative liabilities	$ 0	$ 0