Acquisitions and Divestitures (Gain Loss On Sale of Assets from Continuing Operations) (Details) (USD $)	3 Months Ended		6 Months Ended
	Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2012	Jun. 30, 2011
Gain Loss on Sale of Assets [Line Items]
Gain (loss) on disposition of assets, net	$ 1,140,000	$ (296,000)	$ 44,736,000	$ (2,487,000)
Eagle Ford Shale [Member]
Gain Loss on Sale of Assets [Line Items]
Sale of interest in an unproved oil and gas property			54,700,000
Gain (loss) on disposition of assets in continuing operations			$ 42,600,000