DEBT OBLIGATIONS AND CREDIT FACILITIES - Collateralized Loan Obligation Loans Payable (Details) - Collateralized Loan Obligations - Consolidated Funds - USD ($) $ in Thousands	6 Months Ended	12 Months Ended
	Jun. 30, 2017	Dec. 31, 2016
Debt Instrument [Line Items]
Fair Value	$ 3,100,029	$ 3,054,210
Senior variable rate notes 1
Debt Instrument [Line Items]
Fair Value	$ 398,563	$ 471,603
Weighted Average Interest Rate	3.01%	2.90%
Weighted Average Remaining Maturity (years)	12 years	8 years 2 months 12 days
Senior variable rate notes 2
Debt Instrument [Line Items]
Fair Value	$ 458,294	$ 470,298
Weighted Average Interest Rate	2.92%	3.03%
Weighted Average Remaining Maturity (years)	9 years 4 months 24 days	9 years 10 months 24 days
Senior variable rate notes 3
Debt Instrument [Line Items]
Fair Value	$ 24,129	$ 49,336
Weighted Average Interest Rate	3.62%	3.31%
Weighted Average Remaining Maturity (years)	1 year 6 months	2 years
Senior variable rate notes 3 | Estimate of Fair Value Measurement | Minimum
Debt Instrument [Line Items]
Unused commitment fee	0.00%
Senior variable rate notes 3 | Estimate of Fair Value Measurement | Maximum
Debt Instrument [Line Items]
Unused commitment fee	2.00%
Senior variable rate notes 4
Debt Instrument [Line Items]
Fair Value	$ 385,301	$ 357,706
Weighted Average Interest Rate	1.73%	1.73%
Weighted Average Remaining Maturity (years)	10 years 2 months 12 days	10 years 8 months 12 days
Senior variable rate notes 4 | Estimate of Fair Value Measurement | EURIBOR
Debt Instrument [Line Items]
Base rate	0.00%
Senior variable rate notes 5
Debt Instrument [Line Items]
Fair Value	$ 462,930	$ 467,084
Weighted Average Interest Rate	3.23%	2.96%
Weighted Average Remaining Maturity (years)	10 years 6 months	11 years
Senior variable rate notes 6
Debt Instrument [Line Items]
Fair Value	$ 411,248	$ 360,234
Weighted Average Interest Rate	1.73%	2.29%
Weighted Average Remaining Maturity (years)	13 years 1 month 6 days	11 years 3 months 15 days
Senior variable rate notes 7
Debt Instrument [Line Items]
Fair Value	$ 424,810	$ 395,458
Weighted Average Interest Rate	2.28%	2.28%
Weighted Average Remaining Maturity (years)	11 years 10 months 24 days	12 years 4 months 24 days
Senior variable rate notes 8
Debt Instrument [Line Items]
Fair Value	$ 423,486	$ 382,161
Weighted Average Interest Rate	1.99%	1.99%
Weighted Average Remaining Maturity (years)	12 years 8 months 12 days	13 years 2 months 12 days
Subordinated note 1
Debt Instrument [Line Items]
Fair Value	$ 17,024	$ 12,281
Weighted Average Remaining Maturity (years)	9 years 4 months 24 days	9 years 10 months 24 days
Subordinated note 2
Debt Instrument [Line Items]
Fair Value	$ 19,601	$ 17,871
Weighted Average Remaining Maturity (years)	10 years 2 months 12 days	10 years 8 months 12 days
Subordinated note 3
Debt Instrument [Line Items]
Fair Value	$ 18,952	$ 18,432
Weighted Average Remaining Maturity (years)	10 years 6 months	11 years
Subordinated note 4
Debt Instrument [Line Items]
Fair Value	$ 17,115	$ 13,422
Weighted Average Remaining Maturity (years)	13 years 1 month 6 days	11 years 3 months 15 days
Subordinated note 5
Debt Instrument [Line Items]
Fair Value	$ 20,096	$ 17,073
Weighted Average Remaining Maturity (years)	11 years 10 months 24 days	12 years 4 months 24 days
Subordinated note 6
Debt Instrument [Line Items]
Fair Value	$ 18,480	$ 21,251
Weighted Average Remaining Maturity (years)	12 years 8 months 12 days	13 years 2 months 12 days