Derivatives and Risk Management (Before Tax Effect of Basis Swaps that do not Qualify for Hedge Accounting Consolidated Statements of Operations) (Details) (Gas Sales [Member], Basis Swaps [Member], USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011
Gas Sales [Member] | Basis Swaps [Member]
Derivative [Line Items]
Derivative Instruments, Unrealized Loss Recognized in Earnings	$ (1,275)	$ (1,967)	$ (270)	$ (159)
Derivative Instruments, Realized Gain (Loss) Recognized in Earnings	$ 624	$ (22)	$ 1,773	$ (2,377)