Commitments and Contingencies (Details Textual) (USD $)	12 Months Ended
	Dec. 31, 2011 Secured_lenders Y	Dec. 31, 2010	Dec. 31, 2009
Commitments and Contingencies (Textual) [Abstract]
Rent expense under operating leases	$ 18,600,000	$ 18,500,000	$ 18,800,000
Number of drilling rigs used under drilling contracts	3
Maximum period of drilling contracts in years	3
Maximum penalties on Early termination of drilling contracts	22,200,000
Minimum remaining terms of leases on undeveloped acreage, in years	3
Maximum remaining terms of leases on undeveloped acreage, in years	5
2012 [Member]
Commitments And Contingencies [Line Items]
Amount of lease agreement for hydraulic fracturing services	70,100,000
Drilling contracts, future minimum commitments	25,000,000
Incremental increase in gas production, Mcf per day in Appalachia	143,000
Amount of agreement to purchase seismic data	7,200,000
2013 [Member]
Commitments And Contingencies [Line Items]
Amount of lease agreement for hydraulic fracturing services	52,600,000
Drilling contracts, future minimum commitments	14,700,000
Incremental increase in gas production, Mcf per day in Appalachia	251,900
Amount of agreement to purchase seismic data	1,800,000
2014 [Member]
Commitments And Contingencies [Line Items]
Drilling contracts, future minimum commitments	$ 896,000
Incremental increase in gas production, Mcf per day in Appalachia	346,400
2015 [Member]
Commitments And Contingencies [Line Items]
Incremental increase in gas production, Mcf per day in Appalachia	363,000
2016 [Member]
Commitments And Contingencies [Line Items]
Incremental increase in gas production, Mcf per day in Appalachia	438,800
Thereafter [Member]
Commitments And Contingencies [Line Items]
Incremental increase in gas production, Mcf per day in Appalachia	443,000