DERIVATIVE INSTRUMENTS 3 (Details) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2015		Dec. 31, 2014
Commodity Contract
Offsetting Derivative Assets [Abstract]
Gross amounts of recognized assets/liabilities	$ 67,843		$ 99,273
Gross amount offset in the balance sheet	0		0
Net amounts of assets/liabilities in balance sheet	67,843		99,273
Gross amounts not offset in the balance sheet, Financial Instruments	(24,796)	[1]	(39,747)	[1]
Gross amounts not offset in the balance sheet, Cash Collateral Posted	0		0
Net amount	43,047		59,526
Offsetting Derivative Liabilities [Abstract]
Gross amounts of recognized assets/liabilities	(106,301)		(129,670)
Gross amount offset in the balance sheet	0		0
Net amounts of assets/liabilities in balance sheet	(106,301)		(129,670)
Gross amounts not offset in the balance sheet, Financial Instruments	24,796	[2]	39,747	[2]
Gross amounts not offset in the balance sheet, Cash Collateral Posted	42,770		53,897
Net amount	(38,735)		(36,026)
Interest Rate Contract
Offsetting Derivative Liabilities [Abstract]
Gross amounts of recognized assets/liabilities	(12,036)		(10,732)
Gross amount offset in the balance sheet	0		0
Net amounts of assets/liabilities in balance sheet	(12,036)		(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	$ (12,036)		$ (10,732)

[1] The balances at March 31, 2015 and December 31, 2014 were related to derivative liabilities which can be net settled against derivative assets.

[2] The balances at March 31, 2015 and December 31, 2014 were related to derivative assets which can be net settled against derivative liabilities.