INVESTMENTS (Investments of the Consolidated Funds) (Details) $ in Thousands	6 Months Ended	12 Months Ended
	Jun. 30, 2017 USD ($) issuer	Dec. 31, 2016 USD ($) issuer
Investments
Number of single issuers above 5% | issuer	0
Single issuer or investor threshold, as a percent	5.00%
Consolidated Funds
Investments
Investments, at fair value	$ 3,441,802	$ 3,330,203
Number of single issuers above 5% | issuer	0	0
Single issuer or investor threshold, as a percent	5.00%	5.00%
Consolidated Funds | Fixed Income
Investments
Investments, at fair value	$ 3,022,747	$ 2,953,564
Fair value as a percentage of total investments	87.90%	88.80%
Consolidated Funds | Equity securities
Investments
Investments, at fair value	$ 419,055	$ 376,639
Fair value as a percentage of total investments	12.10%	11.20%
Consolidated Funds | United States | Fixed Income
Investments
Investments, at fair value	$ 1,954,303	$ 1,955,301
Fair value as a percentage of total investments	56.70%	58.70%
Investments, at cost	$ 1,956,026	$ 1,945,977
Consolidated Funds | United States | Fixed Income | Consumer discretionary
Investments
Investments, at fair value	$ 753,922	$ 665,773
Fair value as a percentage of total investments	21.80%	20.00%
Consolidated Funds | United States | Fixed Income | Consumer staples
Investments
Investments, at fair value	$ 45,708	$ 64,840
Fair value as a percentage of total investments	1.30%	1.90%
Consolidated Funds | United States | Fixed Income | Energy
Investments
Investments, at fair value	$ 74,433	$ 45,409
Fair value as a percentage of total investments	2.20%	1.40%
Consolidated Funds | United States | Fixed Income | Financials
Investments
Investments, at fair value	$ 162,618	$ 139,285
Fair value as a percentage of total investments	4.70%	4.20%
Consolidated Funds | United States | Fixed Income | Healthcare, education and childcare
Investments
Investments, at fair value	$ 264,325	$ 246,403
Fair value as a percentage of total investments	7.70%	7.40%
Consolidated Funds | United States | Fixed Income | Industrials
Investments
Investments, at fair value	$ 142,110	$ 149,632
Fair value as a percentage of total investments	4.10%	4.50%
Consolidated Funds | United States | Fixed Income | Information technology
Investments
Investments, at fair value	$ 122,366	$ 194,394
Fair value as a percentage of total investments	3.60%	5.80%
Consolidated Funds | United States | Fixed Income | Materials
Investments
Investments, at fair value	$ 130,831	$ 139,994
Fair value as a percentage of total investments	3.80%	4.20%
Consolidated Funds | United States | Fixed Income | Telecommunication services
Investments
Investments, at fair value	$ 217,617	$ 261,771
Fair value as a percentage of total investments	6.30%	7.90%
Consolidated Funds | United States | Fixed Income | Utilities
Investments
Investments, at fair value	$ 40,373	$ 47,800
Fair value as a percentage of total investments	1.20%	1.40%
Consolidated Funds | United States | Equity securities
Investments
Investments, at fair value	$ 218,011	$ 172,117
Fair value as a percentage of total investments	6.30%	5.20%
Investments, at cost	$ 192,265	$ 149,872
Consolidated Funds | United States | Equity securities | Energy
Investments
Investments, at fair value	$ 271	$ 421
Fair value as a percentage of total investments	0.00%	0.00%
Consolidated Funds | United States | Equity securities | Partnership and LLC interests
Investments
Investments, at fair value	$ 217,740	$ 171,696
Fair value as a percentage of total investments	6.30%	5.20%
Consolidated Funds | Europe | Fixed Income
Investments
Investments, at fair value	$ 994,622	$ 869,474
Fair value as a percentage of total investments	29.10%	26.20%
Investments, at cost	$ 1,050,273	$ 892,108
Consolidated Funds | Europe | Fixed Income | Consumer discretionary
Investments
Investments, at fair value	$ 353,662	$ 274,678
Fair value as a percentage of total investments	10.30%	8.20%
Consolidated Funds | Europe | Fixed Income | Consumer staples
Investments
Investments, at fair value	$ 53,666	$ 39,197
Fair value as a percentage of total investments	1.60%	1.20%
Consolidated Funds | Europe | Fixed Income | Financials
Investments
Investments, at fair value	$ 54,523	$ 28,769
Fair value as a percentage of total investments	1.60%	0.90%
Consolidated Funds | Europe | Fixed Income | Healthcare, education and childcare
Investments
Investments, at fair value	$ 139,683	$ 111,589
Fair value as a percentage of total investments	4.10%	3.40%
Consolidated Funds | Europe | Fixed Income | Industrials
Investments
Investments, at fair value	$ 84,965	$ 118,466
Fair value as a percentage of total investments	2.50%	3.60%
Consolidated Funds | Europe | Fixed Income | Information technology
Investments
Investments, at fair value	$ 39,657	$ 49,507
Fair value as a percentage of total investments	1.20%	1.50%
Consolidated Funds | Europe | Fixed Income | Materials
Investments
Investments, at fair value	$ 151,706	$ 124,629
Fair value as a percentage of total investments	4.40%	3.70%
Consolidated Funds | Europe | Fixed Income | Telecommunication services
Investments
Investments, at fair value	$ 104,514	$ 118,632
Fair value as a percentage of total investments	3.00%	3.60%
Consolidated Funds | Europe | Fixed Income | Utilities
Investments
Investments, at fair value	$ 12,246	$ 4,007
Fair value as a percentage of total investments	0.40%	0.10%
Consolidated Funds | Europe | Equity securities
Investments
Investments, at fair value	$ 46,708	$ 42,870
Fair value as a percentage of total investments	1.30%	1.20%
Investments, at cost	$ 67,199	$ 67,290
Consolidated Funds | Europe | Equity securities | Consumer staples
Investments
Investments, at fair value	$ 1,645	$ 1,517
Fair value as a percentage of total investments	0.00%	0.00%
Consolidated Funds | Europe | Equity securities | Healthcare, education and childcare
Investments
Investments, at fair value	$ 45,063	$ 41,329
Fair value as a percentage of total investments	1.30%	1.20%
Consolidated Funds | Europe | Equity securities | Telecommunication services
Investments
Investments, at fair value	$ 0	$ 24
Fair value as a percentage of total investments	0.00%	0.00%
Consolidated Funds | Asia and other | Fixed Income
Investments
Investments, at fair value	$ 32,504	$ 44,188
Fair value as a percentage of total investments	0.90%	1.30%
Investments, at cost	$ 32,149	$ 46,545
Consolidated Funds | Asia and other | Fixed Income | Consumer discretionary
Investments
Investments, at fair value	$ 20,587	$ 24,244
Fair value as a percentage of total investments	0.60%	0.70%
Consolidated Funds | Asia and other | Fixed Income | Financials
Investments
Investments, at fair value	$ 0	$ 1,238
Fair value as a percentage of total investments	0.00%	0.00%
Consolidated Funds | Asia and other | Fixed Income | Healthcare, education and childcare
Investments
Investments, at fair value	$ 0	$ 10,010
Fair value as a percentage of total investments	0.00%	0.30%
Consolidated Funds | Asia and other | Fixed Income | Telecommunication services
Investments
Investments, at fair value	$ 11,917	$ 8,696
Fair value as a percentage of total investments	0.30%	0.30%
Consolidated Funds | Asia and other | Equity securities
Investments
Investments, at fair value	$ 146,804	$ 143,919
Fair value as a percentage of total investments	4.30%	4.30%
Investments, at cost	$ 122,418	$ 122,418
Consolidated Funds | Asia and other | Equity securities | Consumer discretionary
Investments
Investments, at fair value	$ 38,843	$ 44,642
Fair value as a percentage of total investments	1.10%	1.30%
Consolidated Funds | Asia and other | Equity securities | Consumer staples
Investments
Investments, at fair value	$ 46,746	$ 50,101
Fair value as a percentage of total investments	1.40%	1.50%
Consolidated Funds | Asia and other | Equity securities | Healthcare, education and childcare
Investments
Investments, at fair value	$ 44,637	$ 32,598
Fair value as a percentage of total investments	1.30%	1.00%
Consolidated Funds | Asia and other | Equity securities | Industrials
Investments
Investments, at fair value	$ 16,578	$ 16,578
Fair value as a percentage of total investments	0.50%	0.50%
Consolidated Funds | Canada | Fixed Income
Investments
Investments, at fair value	$ 34,454	$ 48,848
Fair value as a percentage of total investments	1.00%	1.50%
Investments, at cost	$ 34,299	$ 48,274
Consolidated Funds | Canada | Fixed Income | Consumer discretionary
Investments
Investments, at fair value	$ 3,277	$ 0
Fair value as a percentage of total investments	0.10%	0.00%
Consolidated Funds | Canada | Fixed Income | Consumer staples
Investments
Investments, at fair value	$ 2,764	$ 5,256
Fair value as a percentage of total investments	0.10%	0.20%
Consolidated Funds | Canada | Fixed Income | Energy
Investments
Investments, at fair value	$ 16,488	$ 12,830
Fair value as a percentage of total investments	0.50%	0.40%
Consolidated Funds | Canada | Fixed Income | Healthcare, education and childcare
Investments
Investments, at fair value	$ 0	$ 15,509
Fair value as a percentage of total investments	0.00%	0.50%
Consolidated Funds | Canada | Fixed Income | Industrials
Investments
Investments, at fair value	$ 1,266	$ 1,401
Fair value as a percentage of total investments	0.00%	0.00%
Consolidated Funds | Canada | Fixed Income | Telecommunication services
Investments
Investments, at fair value	$ 10,659	$ 13,852
Fair value as a percentage of total investments	0.30%	0.40%
Consolidated Funds | Canada | Equity securities
Investments
Investments, at fair value	$ 7,532	$ 164
Fair value as a percentage of total investments	0.20%	0.00%
Investments, at cost	$ 17,202	$ 408
Consolidated Funds | Canada | Equity securities | Energy
Investments
Investments, at fair value	$ 7,532	$ 164
Fair value as a percentage of total investments	0.20%	0.00%
Consolidated Funds | Australia | Fixed Income
Investments
Investments, at fair value	$ 6,864	$ 35,753
Fair value as a percentage of total investments	0.20%	1.10%
Investments, at cost	$ 8,087	$ 37,975
Consolidated Funds | Australia | Fixed Income | Consumer discretionary
Investments
Investments, at fair value	$ 4,347	$ 5,627
Fair value as a percentage of total investments	0.10%	0.20%
Consolidated Funds | Australia | Fixed Income | Energy
Investments
Investments, at fair value	$ 2,517	$ 6,046
Fair value as a percentage of total investments	0.10%	0.20%
Consolidated Funds | Australia | Fixed Income | Industrials
Investments
Investments, at fair value	$ 0	$ 2,926
Fair value as a percentage of total investments	0.00%	0.10%
Consolidated Funds | Australia | Fixed Income | Utilities
Investments
Investments, at fair value	$ 0	$ 21,154
Fair value as a percentage of total investments	0.00%	0.60%
Consolidated Funds | Australia | Equity securities
Investments
Investments, at fair value	$ 0	$ 17,569
Fair value as a percentage of total investments	0.00%	0.50%
Investments, at cost	$ 0	$ 18,442
Consolidated Funds | Australia | Equity securities | Utilities
Investments
Investments, at fair value	$ 0	$ 17,569
Fair value as a percentage of total investments	0.00%	0.50%