Derivative Activities (Gains (Losses) Of Derivative Contacts By Statement Of Operations Location) (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended				6 Months Ended
	Jun. 30, 2013		Jun. 30, 2012		Jun. 30, 2013		Jun. 30, 2012
Derivative Instruments, Gain (Loss) [Line Items]
Gain (loss) on derivative instrument	$ 50,329		$ 121,568		$ 34,205		$ 94,544
Unrealized gain (loss) on derivative instrument					19,807		76,880
Commodity Contract [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Gain (loss) on derivative instrument	49,523	[1]	126,597	[1]	33,517	[1]	101,462	[1]
Interest Rate Contract [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Gain (loss) on derivative instrument	806	[2]	(5,029)	[2]	688	[2]	(6,918)	[2]
Realized Gain (Loss) [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Gain (loss) on derivative instrument	6,233		11,896		14,398		17,664
Realized Gain (Loss) [Member] | Commodity Contract [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Gain (loss) on derivative instrument	7,435	[1]	14,222	[1]	16,745	[1]	22,293	[1]
Realized Gain (Loss) [Member] | Interest Rate Contract [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Gain (loss) on derivative instrument	(1,202)	[2]	(2,326)	[2]	(2,347)	[2]	(4,629)	[2]
Unrealized Gain (Loss) [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Unrealized gain (loss) on derivative instrument	44,096		109,672		19,807		76,880
Unrealized Gain (Loss) [Member] | Commodity Contract [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Gain (loss) on derivative instrument	42,088		112,375		16,772		79,169
Unrealized gain (loss) on derivative instrument	42,088	[1]	112,375	[1]	16,772	[1]	79,169	[1]
Unrealized Gain (Loss) [Member] | Interest Rate Contract [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Unrealized gain (loss) on derivative instrument	$ 2,008	[2]	$ (2,703)	[2]	$ 3,035	[2]	$ (2,289)	[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.