Properties and Equipment (Details) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2013	Dec. 31, 2012
Property, Plant and Equipment
Proved Natural Gas and Crude Oil Properties	$ 1,533,430	$ 2,075,924
Unproved Natural Gas and Crude Oil Properties	315,233	319,327
Total Natural Gas and Crude Oil Properties	1,848,663	2,395,251
Pipelines and Related Facilities	15,749	47,786
Transportation and Other Equipment	28,780	34,858
Land and Buildings	13,612	14,935
Construction in Progress	146,921	67,217
Gross Propertis and Equipment	2,053,725	2,560,047
Accumulated Depreciation, Depletion and Amortization	(514,024)	(943,341)
Property, Plant and Equipment, Net	1,539,701	1,616,706
Divestitures and Assets Held for Sale
Property, Plant and Equipment
Gross Propertis and Equipment	780,000
Accumulated Depreciation, Depletion and Amortization	$ 566,400