DERIVATIVE INSTRUMENTS HEDGING AND NON-HEDGING ACTIVITIES - Asset and Liabilities Subject to Master Netting Agreements (Details) - USD ($)	Mar. 31, 2018	Dec. 31, 2017
Derivative [Line Items]
Gross amounts of recognized assets	$ 18,132,700	$ 5,349,613
Gross amounts offset in the Balance Sheet	0	0
Net amounts of assets presented in the Balance Sheet	18,132,700	5,349,613
Gross amounts not offset in the Balance Sheet, Financial instruments	0	0
Gross amounts not offset in the Balance Sheet, Cash collateral (Received)/Pledged	(13,741,125)	(1,123,463)
Net Amount	4,391,575	4,226,150
Gross amounts of recognized liabilities	(1,177,060,000)	(1,234,522,000)
Gross amounts offset in the Balance Sheet	0	0
Net amounts of liabilities presented in the Balance Sheet	(1,177,060,000)	(1,234,522,000)
Gross amounts not offset in the Balance Sheet, Cash collateral (Received)/Pledged	1,177,060,000	1,234,522,000
Gross amounts not offset in the Balance Sheet, Cash collateral (Received) / Pledged	0	0
Net Amount	0	0
Repurchase agreements
Derivative [Line Items]
Gross amounts of recognized liabilities	(1,177,060,000)	(1,234,522,000)
Gross amounts offset in the Balance Sheet	0	0
Net amounts of liabilities presented in the Balance Sheet	(1,177,060,000)	(1,234,522,000)
Gross amounts not offset in the Balance Sheet, Cash collateral (Received)/Pledged	1,177,060,000	1,234,522,000
Gross amounts not offset in the Balance Sheet, Cash collateral (Received) / Pledged	0	0
Net Amount	0	0
Futures
Derivative [Line Items]
Gross amounts of recognized assets	18,132,700	5,349,613
Gross amounts offset in the Balance Sheet	0	0
Net amounts of assets presented in the Balance Sheet	18,132,700	5,349,613
Gross amounts not offset in the Balance Sheet, Financial instruments	0	0
Gross amounts not offset in the Balance Sheet, Cash collateral (Received)/Pledged	(13,741,125)	(1,123,463)
Net Amount	$ 4,391,575	$ 4,226,150