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], USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011
Basis Swaps [Member]
Derivative [Line Items]
Derivative Instruments, Unrealized Loss Recognized in Earnings	$ 766	$ 5,222
Derivative Instruments, Realized Gain (Loss) Recognized in Earnings	2,125	(2,135)
Call Options Written [Member]
Derivative [Line Items]
Derivative Instruments, Unrealized Loss Recognized in Earnings	$ (4,128)