Natural Gas and Oil Producing Activities (Composition of Net Unevaluated Costs Excluded from Amortization) (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended			72 Months Ended	108 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009	Dec. 31, 2008	Dec. 31, 2011
Property acquisition costs	$ 254,622	$ 143,165	$ 44,513	$ 110,767	$ 553,067	[1]
Exploration and development costs	190,240	20,844	29,527	67,335	307,946	[1]
Capitalized interest	14,651	12,901	10,261	44,064	81,877	[1]
Net unevaluated costs excluded from amortization	459,513	176,910	84,301	222,166	942,890	[1]
Exploration Program in Canada [Member]
Property acquisition costs	7,500
Exploration and development costs	19,200
Capitalized interest	1,200
Net unevaluated costs excluded from amortization	27,900
Seismic Costs Fayetteville Shale Play [Member]
Net unevaluated costs excluded from amortization	83,200
Undeveloped Properties Fayetteville Shale Play [Member]
Net unevaluated costs excluded from amortization	101,300
Undeveloped Properties Marcellus Shale Play [Member]
Net unevaluated costs excluded from amortization	179,400
Undeveloped Properties New Ventures - Excluding Canada [Member]
Net unevaluated costs excluded from amortization	245,000
Exploration Program in Canada [Member]
Net unevaluated costs excluded from amortization	27,900	10,700
Wells In Progress [Member]
Net unevaluated costs excluded from amortization	$ 180,200

[1] (1) Property acquisition costs include $7.5 million, exploration costs include $19.2 million and capitalized interest includes $1.2 million related to our exploration program in New Brunswick, Canada.