FAIR VALUE OF FINANCIAL INSTRUMENTS (Details 4)	6 Months Ended	12 Months Ended
	Jun. 30, 2017 USD ($) $ / barrel	Dec. 31, 2016 USD ($) $ / shares $ / barrel	Dec. 31, 2015 USD ($)
Crude Oil
Valuation techniques used for assets, measured at fair value
Percentage of share in total revenue	23.00%	23.00%
Natural Gas
Valuation techniques used for assets, measured at fair value
Percentage of share in total revenue	77.00%	77.00%
Natural Resources
Valuation techniques used for assets, measured at fair value
Assets, fair value	$ 78,000,000		$ 107,300,000
Minimum
Valuation techniques used for assets, measured at fair value
Weight ascribed to each valuation technique	0.00%	0.00%
Maximum
Valuation techniques used for assets, measured at fair value
Weight ascribed to each valuation technique	100.00%	100.00%
Significant Unobservable Inputs (Level 3) | Corporate Debt Securities
Valuation techniques used for assets, measured at fair value
Assets, fair value	$ 232,960,000	$ 175,206,000
Significant Unobservable Inputs (Level 3) | Residential Mortgage- Backed Securities
Valuation techniques used for assets, measured at fair value
Assets, fair value	26,112,000	40,663,000
Significant Unobservable Inputs (Level 3) | Corporate Loans
Valuation techniques used for assets, measured at fair value
Assets, fair value	109,405,000	129,194,000
Significant Unobservable Inputs (Level 3) | Equity Investments, at Estimated Fair Value
Valuation techniques used for assets, measured at fair value
Assets, fair value	$ 390,811,000	$ 132,305,000
Significant Unobservable Inputs (Level 3) | Equity Investments, at Estimated Fair Value | Minimum
Valuation techniques used for assets, measured at fair value
Illiquidity discount	5.00%	5.00%
Significant Unobservable Inputs (Level 3) | Corporate Debt Securities and Equity Investments
Valuation techniques used for assets, measured at fair value
Assets, fair value	$ 630,100,000	$ 408,100,000
Significant Unobservable Inputs (Level 3) | Interests in Joint Ventures and Partnerships
Valuation techniques used for assets, measured at fair value
Assets, fair value	1,009,737,000	793,996,000
Significant Unobservable Inputs (Level 3) | Foreign Exchange Options, Net
Valuation techniques used for assets, measured at fair value
Assets, fair value	607,000	992,000
Significant Unobservable Inputs (Level 3) | Options
Valuation techniques used for assets, measured at fair value
Assets, fair value	1,587,000	1,001,000
Significant Unobservable Inputs (Level 3) | Warrants
Valuation techniques used for assets, measured at fair value
Assets, fair value	$ 1,800,000	$ 1,500,000
Yield analysis | Significant Unobservable Inputs (Level 3) | Corporate Debt Securities | Weighted Average
Valuation techniques used for assets, measured at fair value
Yield	21.00%	14.00%
Net leverage	19	9
EBITDA multiple	18	6
Discount margin	12.63%	11.05%
Yield analysis | Significant Unobservable Inputs (Level 3) | Corporate Debt Securities | Minimum
Valuation techniques used for assets, measured at fair value
Yield	5.00%	5.00%
Net leverage	14	7
EBITDA multiple	0	0
Discount margin	12.00%	11.00%
Yield analysis | Significant Unobservable Inputs (Level 3) | Corporate Debt Securities | Maximum
Valuation techniques used for assets, measured at fair value
Yield	22.00%	15.00%
Net leverage	20	16
EBITDA multiple	19	9
Discount margin	16.00%	11.50%
Yield analysis | Significant Unobservable Inputs (Level 3) | Corporate Loans | Weighted Average
Valuation techniques used for assets, measured at fair value
Yield	11.00%	13.00%
Net leverage	10	11
EBITDA multiple	6	6
Weight ascribed to market comparables	1.00%
Weight ascribed to discounted cash flows	1.00%
Weight ascribed to yield analysis	98.00%
Yield analysis | Significant Unobservable Inputs (Level 3) | Corporate Loans | Minimum
Valuation techniques used for assets, measured at fair value
Yield	9.00%	11.00%
Net leverage	5	5
EBITDA multiple	0	0
Weight ascribed to market comparables	0.00%
Weight ascribed to discounted cash flows	0.00%
Weight ascribed to yield analysis	0.00%
Yield analysis | Significant Unobservable Inputs (Level 3) | Corporate Loans | Maximum
Valuation techniques used for assets, measured at fair value
Yield	14.00%	16.00%
Net leverage	15	82
EBITDA multiple	14	19
Weight ascribed to market comparables	50.00%
Weight ascribed to discounted cash flows	50.00%
Weight ascribed to yield analysis	100.00%
Yield analysis | Significant Unobservable Inputs (Level 3) | Interests in Joint Ventures and Partnerships
Valuation techniques used for assets, measured at fair value
Assets, fair value	$ 23,500,000	$ 24,400,000
Yield analysis | Significant Unobservable Inputs (Level 3) | Interests in Joint Ventures and Partnerships | Weighted Average
Valuation techniques used for assets, measured at fair value
Yield	16.00%	19.00%
Net leverage	3	2
EBITDA multiple	10	7
Yield analysis | Significant Unobservable Inputs (Level 3) | Interests in Joint Ventures and Partnerships | Minimum
Valuation techniques used for assets, measured at fair value
Yield	16.00%	19.00%
Net leverage	3	2
EBITDA multiple	10	7
Yield analysis | Significant Unobservable Inputs (Level 3) | Interests in Joint Ventures and Partnerships | Maximum
Valuation techniques used for assets, measured at fair value
Yield	16.00%	19.00%
Net leverage	3	2
EBITDA multiple	10	7
Discounted cash flows | Significant Unobservable Inputs (Level 3) | Residential Mortgage- Backed Securities | Weighted Average
Valuation techniques used for assets, measured at fair value
Probability of default	2.00%	2.00%
Loss severity	43.00%	43.00%
Constant prepayment rate	15.00%	18.00%
Discounted cash flows | Significant Unobservable Inputs (Level 3) | Residential Mortgage- Backed Securities | Minimum
Valuation techniques used for assets, measured at fair value
Probability of default	0.00%	0.00%
Loss severity	35.00%	35.00%
Constant prepayment rate	12.00%	12.00%
Discounted cash flows | Significant Unobservable Inputs (Level 3) | Residential Mortgage- Backed Securities | Maximum
Valuation techniques used for assets, measured at fair value
Probability of default	3.00%	3.00%
Loss severity	50.00%	50.00%
Constant prepayment rate	18.00%	23.00%
Discounted cash flows | Significant Unobservable Inputs (Level 3) | Corporate Loans | Weighted Average
Valuation techniques used for assets, measured at fair value
Weighted average cost of capital	12.00%
LTM EBITDA exit multiple	7
Discounted cash flows | Significant Unobservable Inputs (Level 3) | Corporate Loans | Minimum
Valuation techniques used for assets, measured at fair value
Weighted average cost of capital	12.00%
LTM EBITDA exit multiple	7
Discounted cash flows | Significant Unobservable Inputs (Level 3) | Corporate Loans | Maximum
Valuation techniques used for assets, measured at fair value
Weighted average cost of capital	12.00%
LTM EBITDA exit multiple	7
Discounted cash flows | Significant Unobservable Inputs (Level 3) | Equity Investments, at Estimated Fair Value
Valuation techniques used for assets, measured at fair value
Assets, fair value	$ 11,800,000	$ 20,000,000
Discounted cash flows | Significant Unobservable Inputs (Level 3) | Equity Investments, at Estimated Fair Value | Weighted Average
Valuation techniques used for assets, measured at fair value
Weighted average cost of capital	9.00%	9.00%
LTM EBITDA exit multiple	8	8
Discounted cash flows | Significant Unobservable Inputs (Level 3) | Equity Investments, at Estimated Fair Value | Minimum
Valuation techniques used for assets, measured at fair value
Weighted average cost of capital	6.00%	7.00%
LTM EBITDA exit multiple	6	7
Discounted cash flows | Significant Unobservable Inputs (Level 3) | Equity Investments, at Estimated Fair Value | Maximum
Valuation techniques used for assets, measured at fair value
Weighted average cost of capital	14.00%	14.00%
LTM EBITDA exit multiple	10	10
Discounted cash flows | Significant Unobservable Inputs (Level 3) | Interests in Joint Ventures and Partnerships
Valuation techniques used for assets, measured at fair value
Assets, fair value	$ 45,100,000	$ 43,500,000
Discounted cash flows | Significant Unobservable Inputs (Level 3) | Interests in Joint Ventures and Partnerships | Weighted Average
Valuation techniques used for assets, measured at fair value
Weighted average cost of capital	9.00%	10.00%
Average price per BOE (in dollars per barrel) | $ / barrel	19.11	20.26
Discounted cash flows | Significant Unobservable Inputs (Level 3) | Interests in Joint Ventures and Partnerships | Minimum
Valuation techniques used for assets, measured at fair value
Weighted average cost of capital	6.00%	6.00%
Average price per BOE (in dollars per barrel) | $ / barrel	17.53	18.81
Discounted cash flows | Significant Unobservable Inputs (Level 3) | Interests in Joint Ventures and Partnerships | Maximum
Valuation techniques used for assets, measured at fair value
Weighted average cost of capital	20.00%	20.00%
Average price per BOE (in dollars per barrel) | $ / barrel	20.85	22.38
Discounted cash flows | Significant Unobservable Inputs (Level 3) | Options | Weighted Average
Valuation techniques used for assets, measured at fair value
Weighted average cost of capital	12.00%	15.00%
LTM EBITDA exit multiple	7	5
Discounted cash flows | Significant Unobservable Inputs (Level 3) | Options | Minimum
Valuation techniques used for assets, measured at fair value
Weighted average cost of capital	12.00%	15.00%
LTM EBITDA exit multiple	7	5
Discounted cash flows | Significant Unobservable Inputs (Level 3) | Options | Maximum
Valuation techniques used for assets, measured at fair value
Weighted average cost of capital	12.00%	15.00%
LTM EBITDA exit multiple	7	5
Option pricing model | Significant Unobservable Inputs (Level 3) | Weighted Average | Foreign Exchange Options, Net
Valuation techniques used for assets, measured at fair value
Forward and spot rates	$ 13,345	$ 10,301
Option pricing model | Significant Unobservable Inputs (Level 3) | Minimum | Foreign Exchange Options, Net
Valuation techniques used for assets, measured at fair value
Forward and spot rates	13,345	6
Option pricing model | Significant Unobservable Inputs (Level 3) | Maximum | Foreign Exchange Options, Net
Valuation techniques used for assets, measured at fair value
Forward and spot rates	$ 13,345	$ 13,550
Market comparables | Significant Unobservable Inputs (Level 3) | Corporate Debt Securities | Weighted Average
Valuation techniques used for assets, measured at fair value
LTM EBITDA multiple		12
Market comparables | Significant Unobservable Inputs (Level 3) | Corporate Debt Securities | Minimum
Valuation techniques used for assets, measured at fair value
LTM EBITDA multiple		12
Market comparables | Significant Unobservable Inputs (Level 3) | Corporate Debt Securities | Maximum
Valuation techniques used for assets, measured at fair value
LTM EBITDA multiple		12
Market comparables | Significant Unobservable Inputs (Level 3) | Corporate Loans | Weighted Average
Valuation techniques used for assets, measured at fair value
LTM EBITDA multiple	8
Forward EBITDA multiple	9
Market comparables | Significant Unobservable Inputs (Level 3) | Corporate Loans | Minimum
Valuation techniques used for assets, measured at fair value
LTM EBITDA multiple	8
Forward EBITDA multiple	9
Market comparables | Significant Unobservable Inputs (Level 3) | Corporate Loans | Maximum
Valuation techniques used for assets, measured at fair value
LTM EBITDA multiple	8
Forward EBITDA multiple	9
Market comparables | Significant Unobservable Inputs (Level 3) | Equity Investments, at Estimated Fair Value
Valuation techniques used for assets, measured at fair value
Assets, fair value	$ 10,600,000	$ 14,500,000
Market comparables | Significant Unobservable Inputs (Level 3) | Equity Investments, at Estimated Fair Value | Weighted Average
Valuation techniques used for assets, measured at fair value
LTM EBITDA multiple	12	11
Forward EBITDA multiple	12	9
Market comparables | Significant Unobservable Inputs (Level 3) | Equity Investments, at Estimated Fair Value | Minimum
Valuation techniques used for assets, measured at fair value
LTM EBITDA multiple	0	0
Forward EBITDA multiple	0	0
Market comparables | Significant Unobservable Inputs (Level 3) | Equity Investments, at Estimated Fair Value | Maximum
Valuation techniques used for assets, measured at fair value
LTM EBITDA multiple	15	14
Forward EBITDA multiple	14	13
Market comparables | Significant Unobservable Inputs (Level 3) | Interests in Joint Ventures and Partnerships
Valuation techniques used for assets, measured at fair value
Assets, fair value	$ 9,200,000	$ 9,800,000
Market comparables | Significant Unobservable Inputs (Level 3) | Interests in Joint Ventures and Partnerships | Weighted Average
Valuation techniques used for assets, measured at fair value
LTM EBITDA multiple	1	4
Capitalization rate	6.00%	7.00%
Forward EBITDA multiple	1	9
Market comparables | Significant Unobservable Inputs (Level 3) | Interests in Joint Ventures and Partnerships | Minimum
Valuation techniques used for assets, measured at fair value
LTM EBITDA multiple	1	1
Capitalization rate	3.00%	3.00%
Forward EBITDA multiple	1	9
Market comparables | Significant Unobservable Inputs (Level 3) | Interests in Joint Ventures and Partnerships | Maximum
Valuation techniques used for assets, measured at fair value
LTM EBITDA multiple	1	9
Capitalization rate	12.00%	12.00%
Forward EBITDA multiple	1	9
Market comparables | Significant Unobservable Inputs (Level 3) | Options | Weighted Average
Valuation techniques used for assets, measured at fair value
LTM EBITDA multiple	8	9
Forward EBITDA multiple	9	7
Market comparables | Significant Unobservable Inputs (Level 3) | Options | Minimum
Valuation techniques used for assets, measured at fair value
LTM EBITDA multiple	8	9
Forward EBITDA multiple	9	7
Market comparables | Significant Unobservable Inputs (Level 3) | Options | Maximum
Valuation techniques used for assets, measured at fair value
LTM EBITDA multiple	8	9
Forward EBITDA multiple	9	7
Inputs to both market comparables and discounted cash flow | Significant Unobservable Inputs (Level 3) | Equity Investments, at Estimated Fair Value | Weighted Average
Valuation techniques used for assets, measured at fair value
Weight ascribed to market comparables	49.00%	47.00%
Weight ascribed to discounted cash flows	51.00%	53.00%
Illiquidity discount	10.00%	8.00%
Inputs to both market comparables and discounted cash flow | Significant Unobservable Inputs (Level 3) | Equity Investments, at Estimated Fair Value | Minimum
Valuation techniques used for assets, measured at fair value
Weight ascribed to market comparables	0.00%	0.00%
Weight ascribed to discounted cash flows	0.00%	0.00%
Illiquidity discount	0.00%	5.00%
Inputs to both market comparables and discounted cash flow | Significant Unobservable Inputs (Level 3) | Equity Investments, at Estimated Fair Value | Maximum
Valuation techniques used for assets, measured at fair value
Weight ascribed to market comparables	100.00%	100.00%
Weight ascribed to discounted cash flows	100.00%	100.00%
Illiquidity discount	20.00%	15.00%
Inputs to both market comparables and discounted cash flow | Significant Unobservable Inputs (Level 3) | Interests in Joint Ventures and Partnerships | Weighted Average
Valuation techniques used for assets, measured at fair value
Weight ascribed to market comparables	27.00%	27.00%
Weight ascribed to discounted cash flows	44.00%	45.00%
Weight ascribed to yield analysis	29.00%	28.00%
Inputs to both market comparables and discounted cash flow | Significant Unobservable Inputs (Level 3) | Interests in Joint Ventures and Partnerships | Minimum
Valuation techniques used for assets, measured at fair value
Weight ascribed to market comparables	0.00%	0.00%
Weight ascribed to discounted cash flows	0.00%	0.00%
Weight ascribed to yield analysis	0.00%	0.00%
Inputs to both market comparables and discounted cash flow | Significant Unobservable Inputs (Level 3) | Interests in Joint Ventures and Partnerships | Maximum
Valuation techniques used for assets, measured at fair value
Weight ascribed to market comparables	100.00%	100.00%
Weight ascribed to discounted cash flows	100.00%	100.00%
Weight ascribed to yield analysis	100.00%	100.00%
Inputs to both market comparables and discounted cash flow | Significant Unobservable Inputs (Level 3) | Options
Valuation techniques used for assets, measured at fair value
Weight ascribed to market comparables	50.00%	50.00%
Weight ascribed to discounted cash flows	50.00%	50.00%
Inputs to both market comparables and discounted cash flow | Significant Unobservable Inputs (Level 3) | Options | Weighted Average
Valuation techniques used for assets, measured at fair value
Weight ascribed to market comparables	50.00%	50.00%
Weight ascribed to discounted cash flows	50.00%	50.00%
Illiquidity discount	10.00%	10.00%
Inputs to both market comparables and discounted cash flow | Significant Unobservable Inputs (Level 3) | Options | Minimum
Valuation techniques used for assets, measured at fair value
Weight ascribed to market comparables	50.00%	50.00%
Weight ascribed to discounted cash flows	50.00%	50.00%
Illiquidity discount	10.00%	10.00%
Inputs to both market comparables and discounted cash flow | Significant Unobservable Inputs (Level 3) | Options | Maximum
Valuation techniques used for assets, measured at fair value
Weight ascribed to market comparables	50.00%	50.00%
Weight ascribed to discounted cash flows	50.00%	50.00%
Illiquidity discount	10.00%	10.00%
Black Scholes Options Pricing Model | Significant Unobservable Inputs (Level 3) | Corporate Debt Securities | Weighted Average
Valuation techniques used for assets, measured at fair value
Risk-Free Rate		1.00%
Volatility		85.00%
Black Scholes Options Pricing Model | Significant Unobservable Inputs (Level 3) | Corporate Debt Securities | Minimum
Valuation techniques used for assets, measured at fair value
Risk-Free Rate		1.00%
Volatility		85.00%
Black Scholes Options Pricing Model | Significant Unobservable Inputs (Level 3) | Corporate Debt Securities | Maximum
Valuation techniques used for assets, measured at fair value
Risk-Free Rate		1.00%
Volatility		85.00%
Black Scholes Options Pricing Model | Significant Unobservable Inputs (Level 3) | Corporate Loans | Weighted Average
Valuation techniques used for assets, measured at fair value
Risk-Free Rate	3.00%
Volatility	28.00%
Black Scholes Options Pricing Model | Significant Unobservable Inputs (Level 3) | Corporate Loans | Minimum
Valuation techniques used for assets, measured at fair value
Risk-Free Rate	3.00%
Volatility	28.00%
Black Scholes Options Pricing Model | Significant Unobservable Inputs (Level 3) | Corporate Loans | Maximum
Valuation techniques used for assets, measured at fair value
Risk-Free Rate	3.00%
Volatility	28.00%
Black Scholes Options Pricing Model | Significant Unobservable Inputs (Level 3) | Options | Weighted Average
Valuation techniques used for assets, measured at fair value
Risk-Free Rate	3.00%
Volatility	28.00%
Black Scholes Options Pricing Model | Significant Unobservable Inputs (Level 3) | Options | Minimum
Valuation techniques used for assets, measured at fair value
Risk-Free Rate	3.00%
Volatility	28.00%
Black Scholes Options Pricing Model | Significant Unobservable Inputs (Level 3) | Options | Maximum
Valuation techniques used for assets, measured at fair value
Risk-Free Rate	3.00%
Volatility	28.00%
Offered quotes | Significant Unobservable Inputs (Level 3) | Corporate Debt Securities | Weighted Average
Valuation techniques used for assets, measured at fair value
Offered quotes (in dollars per share) | $ / shares		$ 102
Offered quotes | Significant Unobservable Inputs (Level 3) | Corporate Debt Securities | Minimum
Valuation techniques used for assets, measured at fair value
Offered quotes (in dollars per share) | $ / shares		101
Offered quotes | Significant Unobservable Inputs (Level 3) | Corporate Debt Securities | Maximum
Valuation techniques used for assets, measured at fair value
Offered quotes (in dollars per share) | $ / shares		$ 103