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		6 Months Ended
	Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2012	Jun. 30, 2011
Gas Sales [Member] | Basis Swaps [Member]
Derivative Instruments, Unrealized Gain (Loss) Recognized in Earnings	$ (218)	$ 902	$ 1,005	$ 1,808
Derivative Instruments, Realized Gain (Loss) Recognized in Earnings	$ 131	$ (99)	$ 1,149	$ (2,355)