DERIVATIVE INSTRUMENTS - OFFSETTING ARRANGEMENTS (Details) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Derivatives - Energy Related
Offsetting Derivative Assets [Abstract]
Gross amounts of recognized assets	$ 5,807	$ 1,141
Gross amount offset in the balance sheet	0	0
Net amounts of assets/liabilities in balance sheet	5,807	1,141
Gross amounts not offset in the balance sheet, Financial Instruments	(6)	(399)
Gross amounts not offset in the balance sheet, Cash Collateral Posted	(3,587)	0
Net amount	2,214	742
Offsetting Derivative Liabilities [Abstract]
Gross amounts of recognized liabilities	(1,372)	(5,840)
Gross amount offset in the balance sheet	0	0
Net amounts of assets/liabilities in balance sheet	(1,372)	(5,840)
Gross amounts not offset in the balance sheet, Financial Instruments	6	399
Gross amounts not offset in the balance sheet, Cash Collateral Posted	0	5,025
Net amount	(1,366)	(416)
Derivatives - Other
Offsetting Derivative Liabilities [Abstract]
Gross amounts of recognized liabilities	(7,365)	(7,631)
Gross amount offset in the balance sheet	0	0
Net amounts of assets/liabilities in balance sheet	(7,365)	(7,631)
Gross amounts not offset in the balance sheet, Financial Instruments	0	0
Gross amounts not offset in the balance sheet, Cash Collateral Posted	0	0
Net amount	$ (7,365)	$ (7,631)