Natural Gas And Oil Producing Activities (Unaudited) (Narrative) (Details) (USD $)	12 Months Ended			84 Months Ended	120 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2013
Net unevaluated costs excluded from amortization	$ 322,308,000	$ 141,384,000	$ 307,380,000	$ 185,397,000	$ 956,469,000	[1]
Percentage of present worth of proved reserves evaluated in audit	95.00%	93.00%	90.00%
Capitalized interest based on weighted average cost of borrowings	61,600,000	62,100,000	43,400,000
Capitalized internal costs related to acquisition, exploration and development	262,200,000	236,500,000	207,900,000
Capitalized internal costs related to acquisition, exploration and development activities - subsidiaries	104,300,000	81,700,000	51,300,000
Discount Rate Of Natural Gas And Oil Reserves	10.00%
Seismic Costs Fayetteville Shale Play [Member]
Net unevaluated costs excluded from amortization	23,100,000
Undeveloped Properties Fayetteville Shale Play [Member]
Net unevaluated costs excluded from amortization	39,000,000
Undeveloped Properties Marcellus Shale Play [Member]
Net unevaluated costs excluded from amortization	195,700,000
Undeveloped Properties New Ventures - Excluding Canada [Member]
Net unevaluated costs excluded from amortization	275,800,000
Exploration Program in Canada [Member]
Net unevaluated costs excluded from amortization	72,300,000
Wells In Progress [Member]
Net unevaluated costs excluded from amortization	$ 220,700,000
West Texas Intermediate Oil [Member]
Full cost ceiling test, Price	93.42	91.21	92.71
Henry Hub Natural Gas [Member]
Full cost ceiling test, Price	3.67	2.76	4.12

[1] Property acquisition costs include $35.0 million, exploration costs include $31.8 million and capitalized interest includes $5.5 million related to our exploration program in Canada.