Derivative Activities (Gains (Losses) Of Derivative Contacts By Statement Of Operations Location) (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2013		Mar. 31, 2012
Derivative Instruments, Gain (Loss) [Line Items]
Gain (loss) on derivative instrument	$ (16,124)		$ (27,024)
Unrealized gain (loss) on derivative instrument	(24,289)		(32,792)
Commodity Contract [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Gain (loss) on derivative instrument	(16,006)	[1]	(25,135)	[1]
Interest Rate Contract [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Gain (loss) on derivative instrument	(118)	[2]	(1,889)	[2]
Realized Gain (Loss) [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Gain (loss) on derivative instrument	8,165		5,768
Realized Gain (Loss) [Member] | Commodity Contract [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Gain (loss) on derivative instrument	9,310	[1]	8,071	[1]
Realized Gain (Loss) [Member] | Interest Rate Contract [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Gain (loss) on derivative instrument	(1,145)	[2]	(2,303)	[2]
Unrealized Gain (Loss) [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Unrealized gain (loss) on derivative instrument	(24,289)		(32,792)
Unrealized Gain (Loss) [Member] | Commodity Contract [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Gain (loss) on derivative instrument	(25,316)		(33,206)
Unrealized gain (loss) on derivative instrument	(25,316)	[1]	(33,206)	[1]
Unrealized Gain (Loss) [Member] | Interest Rate Contract [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Unrealized gain (loss) on derivative instrument	$ 1,027	[2]	$ 414	[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.