Derivative Activities (Gains (Losses) Of Derivative Contacts By Statement Of Operations Location) (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended				9 Months Ended
	Sep. 30, 2012		Sep. 30, 2011		Sep. 30, 2012		Sep. 30, 2011
Derivative Instruments, Gain (Loss) [Line Items]
Gain (loss) on derivative instrument	$ (45,382)		$ 98,741		$ 37,904		$ 53,435
Unrealized gain (loss) on derivative instrument					23,011		135,590
Commodity Contract [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Gain (loss) on derivative instrument	(42,210)	[1]	114,306	[1]	47,996	[1]	80,309	[1]
Interest Rate Contract [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Gain (loss) on derivative instrument	(3,172)	[2]	(15,565)	[2]	(10,092)	[2]	(26,874)	[2]
Realized Gain (Loss) [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Gain (loss) on derivative instrument	(2,770)		(40,041)		14,893		(82,155)
Realized Gain (Loss) [Member] | Commodity Contract [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Gain (loss) on derivative instrument	13,375	[1]	(39,072)	[1]	35,668	[1]	(79,924)	[1]
Realized Gain (Loss) [Member] | Interest Rate Contract [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Gain (loss) on derivative instrument	(16,145)	[2]	(969)	[2]	(20,775)	[2]	(2,231)	[2]
Unrealized Gain (Loss) [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Unrealized gain (loss) on derivative instrument	(42,612)		138,782		23,011		135,590
Unrealized Gain (Loss) [Member] | Commodity Contract [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Gain (loss) on derivative instrument	(55,585)		153,378		12,328		160,233
Unrealized gain (loss) on derivative instrument	(55,585)	[1]	153,378	[1]	12,328	[1]	160,233	[1]
Unrealized Gain (Loss) [Member] | Interest Rate Contract [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Unrealized gain (loss) on derivative instrument	$ 12,973	[2]	$ (14,596)	[2]	$ 10,683	[2]	$ (24,643)	[2]

[1] Gain (loss) on commodity derivative contracts is located in other income (expense) in the consolidated statements of operations.

[2] Gain (loss) on interest rate derivatives contracts is recorded as part of interest expense and is located in other income (expense) in the consolidated statements of operations.