OTHER ASSETS AND ACCOUNTS PAYABLE, ACCRUED EXPENSES AND OTHER LIABILITIES - Accounts Payable, Accrued Expenses and Other Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
OTHER ASSETS AND ACCOUNTS PAYABLE, ACCRUED EXPENSES AND OTHER LIABILITIES
Amounts Payable to Carry Pool	$ 922,977	$ 1,220,559
Unsettled Investment Purchases	541,165	885,945
Securities Sold Short	344,124	692,007
Derivative Liabilities	35,640	69,381
Accrued Compensation and Benefits	107,887	35,953
Interest Payable	212,969	168,673
Foreign Exchange Contracts and Options	60,749	260,948
Accounts Payable and Accrued Expenses	130,554	152,916
Taxes Payable	24,453	35,933
Uncertain Tax Positions	66,775	58,369
Unfunded Revolver Commitments	52,066	17,629
Other Liabilities	244,631	55,937
Total	$ 2,743,990	$ 3,654,250