Derivatives And Fair Value Measurements (Narrative) (Details) (USD $)	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013 MMcf	Sep. 30, 2012	Dec. 31, 2010
Anticipated Natural Gas Basis Swap Production For Second Year			40
Realized Gain on Derivative Instruments, Gross, Pretax	$ 8,009,000	$ 12,376,000	$ 14,129,000	$ 35,059,000
Cash received in settlement of hedge					41,500,000
Interest previously accrued and earned					10,700,000
Unrealized Gain (Loss) on Interest Rate Cash Flow Hedges, Pretax, Accumulated Other Comprehensive Income (Loss)					30,800,000
Senior notes maturity					2015
Gain (Loss) on Discontinuation of Interest Rate Cash Flow Hedge Due to Forecasted Transaction Probable of Not Occurring, Net			8,300,000
Interest Rate Cash Flow Hedge Gain (Loss) Reclassified to Earnings, Net			11,500,000	3,800,000
Remaining deferred gains on early settlements from interest rate swaps			5,300,000
Gains and losses from the effective portion of derivative assets and liabilities held in AOCI expected to be reclassified into earnings	$ 29,500,000		$ 29,500,000
Term of derivative instrument			10 years
Gas 2013, MMcfd			200
Anticipated NGL Production For 2013			6
Gas 2014, MMcfd			170
Anticipated NGL Production For Second Year			4
Gas 2015, MMcfd			150
Anticipated NGL Production For Third Year			0
Gas 2016-2021, MMcfd			40
Anticipated NGL Production Thereafter			0
Fair Value Inputs, Level 3 [Member]
Natural gas hedges original tenure			10 years
Fair Value Inputs, Level 3 [Member] | Maximum [Member]
Unobservable inputs included within the fair value calculation	5.61		5.61
Fair Value Inputs, Level 3 [Member] | Minimum [Member]
Unobservable inputs included within the fair value calculation	3.50		3.50