DERIVATIVE INSTRUMENTS (Details 2) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2012	Dec. 31, 2011
Current assets
Derivative contracts not designated as hedging instruments and their balance sheet location
Commodity derivative asset	$ 74,699	$ 79,487
Interest rate derivative asset	10,846	10,134
Total assets	85,545	89,621
Long-term assets
Derivative contracts not designated as hedging instruments and their balance sheet location
Commodity derivative asset	8,831	0
Interest rate derivative asset	6,561	10,422
Total assets	15,392	10,422
Current liabilities
Derivative contracts not designated as hedging instruments and their balance sheet location
Commodity derivative liability	16,670	28,944
Long-term liabilities
Derivative contracts not designated as hedging instruments and their balance sheet location
Commodity derivative liability	$ 7,745	$ 0