Properties and Equipment (Details) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2013	Dec. 31, 2012
Property, Plant and Equipment
Proved Natural Gas and Crude Oil Properties	$ 1,459,066	$ 2,075,924
Unproved Natural Gas and Crude Oil Properties	316,301	319,327
Total Natural Gas and Crude Oil Properties	1,775,367	2,395,251
Pipelines and Related Facilities	15,094	47,786
Transportation and Other Equipment	27,893	34,858
Land and Buildings	13,507	14,935
Construction in Progress	90,452	67,217
Gross Propertis and Equipment	1,922,313	2,560,047
Accumulated Depreciation, Depletion and Amortization	(483,433)	(943,341)
Property, Plant and Equipment, Net	$ 1,438,880	$ 1,616,706