RISK MANAGEMENT (Impact of Derivatives and their Location Within Consolidated Statements of Operations) (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012
Derivative Instruments, Gain (Loss) [Line Items]
Realized gains on derivatives, net	$ 10,759	$ 24,190
Unrealized gains on derivatives, net	(38,273)	11,661
Commodity Contracts [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Realized gains on derivatives, net	12,304	25,306
Unrealized gains on derivatives, net	(39,720)	11,154
Interest Rate Swaps [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Realized gains on derivatives, net	(1,545)	(1,116)
Unrealized gains on derivatives, net	$ 1,447	$ 507