DERIVATIVE INSTRUMENTS 3 (Details) - USD ($) $ in Thousands	Sep. 30, 2015	Dec. 31, 2014
Offsetting Derivative Assets [Abstract]
Gross amounts of recognized assets/liabilities	$ 77,674	$ 99,273
Offsetting Derivative Liabilities [Abstract]
Gross amount offset in the balance sheet	121,801	140,402
Commodity Contract
Offsetting Derivative Assets [Abstract]
Gross amounts of recognized assets/liabilities	77,674	99,273
Gross amount offset in the balance sheet	0	0
Net amounts of assets/liabilities in balance sheet	77,674	99,273
Gross amounts not offset in the balance sheet, Financial Instruments	(30,785)	(39,747)
Gross amounts not offset in the balance sheet, Cash Collateral Posted	0	0
Net amount	46,889	59,526
Offsetting Derivative Liabilities [Abstract]
Gross amounts of recognized assets/liabilities	(110,283)	(129,670)
Gross amount offset in the balance sheet	0	0
Net amounts of assets/liabilities in balance sheet	(110,283)	(129,670)
Gross amounts not offset in the balance sheet, Financial Instruments	30,785	39,747
Gross amounts not offset in the balance sheet, Cash Collateral Posted	30,856	53,897
Net amount	(48,642)	(36,026)
Other Contract
Offsetting Derivative Liabilities [Abstract]
Gross amounts of recognized assets/liabilities	(11,518)	(10,732)
Gross amount offset in the balance sheet	0	0
Net amounts of assets/liabilities in balance sheet	(11,518)	(10,732)
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	$ (11,518)	$ (10,732)