FAIR VALUE - Consolidated Funds Summary of Changes in Fair Value of Level III Investments (Details) - Consolidated Funds - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016	Dec. 31, 2015
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Cumulative-effect adjustment from adoption of accounting guidance					$ (27,012,584)
Fair Value, Net Asset (Liability) Measured On Recurring Basis, Unobservable Input Reconciliation [Roll Forward]
Beginning balance	$ 201,985	$ 195,773	$ 244,354	$ 27,217,707
Transfers into Level III	349	23,375	24,515	61,308
Transfers out of Level III	(7,037)	(765)	(56,157)	(43,435)
Purchases	68,056	13,130	118,627	22,667
Sales	(43,993)	(21,711)	(114,562)	(35,404)
Realized gains (losses), net	(145)	110	464	225
Unrealized appreciation (depreciation), net	2,806	5,065	4,780	4,493
Ending balance	222,021	214,977	222,021	214,977
Net change in unrealized appreciation (depreciation) attributable to assets still held at end of period	2,193	5,065	4,447	4,493
Corporate debt – bank debt
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance	151,229	189,909	208,868	1,871,375
Cumulative-effect adjustment from adoption of accounting guidance					(1,672,305)
Transfers into Level III	349	20,684	22,537	58,219
Transfers out of Level III	(5,059)	(765)	(54,179)	(43,435)
Purchases	44,199	5,178	67,516	14,556
Sales	(28,567)	(19,918)	(83,772)	(32,790)
Realized gains (losses), net	(325)	132	(114)	247
Unrealized appreciation (depreciation), net	2,842	4,754	3,812	4,107
Ending balance	164,668	199,974	164,668	199,974
Net change in unrealized appreciation (depreciation) attributable to assets still held at end of period	2,219	4,754	3,366	4,107
Corporate debt – all other
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance	43,469	1,890	28,793	3,009,164
Cumulative-effect adjustment from adoption of accounting guidance					(3,007,287)
Transfers into Level III	0	0	1,978	0
Transfers out of Level III	(1,978)	0	(1,978)	0
Purchases	21,363	6,808	48,481	6,810
Sales	(13,347)	(2)	(28,072)	(2)
Realized gains (losses), net	175	0	486	0
Unrealized appreciation (depreciation), net	(548)	(18)	(554)	(7)
Ending balance	49,134	8,678	49,134	8,678
Net change in unrealized appreciation (depreciation) attributable to assets still held at end of period	(538)	(18)	(441)	(7)
Equities – common stock
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance	7,287	3,974	6,693	8,729,202
Cumulative-effect adjustment from adoption of accounting guidance					(8,725,026)
Transfers into Level III	0	2,691	0	3,089
Transfers out of Level III	0	0	0	0
Purchases	0	1,144	136	1,301
Sales	(74)	(1,791)	(713)	(2,612)
Realized gains (losses), net		(22)	87	(22)
Unrealized appreciation (depreciation), net	501	329	1,511	393
Ending balance	7,714	6,325	7,714	6,325
Net change in unrealized appreciation (depreciation) attributable to assets still held at end of period	501	329	1,511	393
Equities – preferred stock
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance			0	1,363,542
Cumulative-effect adjustment from adoption of accounting guidance					(1,363,542)
Transfers into Level III			0	0
Transfers out of Level III			0	0
Purchases			0	0
Sales			0	0
Realized gains (losses), net			0	0
Unrealized appreciation (depreciation), net			0	0
Ending balance	0	0	0	0
Net change in unrealized appreciation (depreciation) attributable to assets still held at end of period			0	0
Real estate
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance	0	0	0	9,655,270
Cumulative-effect adjustment from adoption of accounting guidance					(9,655,270)
Transfers into Level III	0	0	0	0
Transfers out of Level III	0	0	0	0
Purchases	2,494	0	2,494	0
Sales	(2,005)	0	(2,005)	0
Realized gains (losses), net	5	0	5	0
Unrealized appreciation (depreciation), net	11	0	11	0
Ending balance	505	0	505	0
Net change in unrealized appreciation (depreciation) attributable to assets still held at end of period	11	0	11	0
Real estate loan portfolios
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance			0	2,597,405
Cumulative-effect adjustment from adoption of accounting guidance					(2,597,405)
Transfers into Level III			0	0
Transfers out of Level III			0	0
Purchases			0	0
Sales			0	0
Realized gains (losses), net			0	0
Unrealized appreciation (depreciation), net			0	0
Ending balance	0	0	0	0
Net change in unrealized appreciation (depreciation) attributable to assets still held at end of period			0	0
Swaps
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Cumulative-effect adjustment from adoption of accounting guidance					$ 8,251
Swaps
Beginning balance			0	(8,251)
Transfers into Level III			0	0
Transfers out of Level III			0	0
Purchases			0	0
Sales			0	0
Realized gains (losses), net			0	0
Unrealized appreciation (depreciation), net			0	0
Ending balance	$ 0	$ 0	0	0
Net change in unrealized appreciation (depreciation) attributable to assets still held at end of period			$ 0	$ 0