OTHER ASSETS AND ACCOUNTS PAYABLE, ACCRUED EXPENSES AND OTHER LIABILITIES - Other Assets (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017
OTHER ASSETS AND ACCOUNTS PAYABLE, ACCRUED EXPENSES AND OTHER LIABILITIES
Unsettled Investment Sales	$ 114,149		$ 114,149		$ 134,781
Receivables	52,223		52,223		138,109
Due from Broker	428,928		428,928		682,403
Oil & Gas Assets, net	221,901		221,901		252,371
Deferred Tax Assets, net	298,336		298,336		131,944
Interest Receivable	227,090		227,090		189,785
Fixed Assets, net	422,388		422,388		364,203
Foreign Exchange Contracts and Options	98,748		98,748		96,584
Intangible Assets, net	10,674		10,674		129,178
Goodwill	83,500		83,500		83,500
Derivative Assets	45,310		45,310		85,074
Deposits	7,646		7,646		16,330
Prepaid Taxes	79,769		79,769		83,371
Prepaid Expenses	29,306		29,306		25,677
Deferred Financing Costs	6,761		6,761		7,534
Other	121,018		121,018		110,231
Total	2,247,747		2,247,747		2,531,075
Depreciation, depletion, and amortization of oil and natural gas properties	4,255	$ 5,466	17,800	$ 18,563
Accumulated depreciation and amortization of fixed assets	168,018		168,018		156,859
Depreciation and amortization expense of fixed assets	3,649	3,710	11,133	11,774
Intangible assets, accumulated amortization	63,188		63,188		$ 61,348
Amortization of intangibles	$ 681	$ 2,473	$ 7,028	$ 13,901