Discontinued Operations and Disposal Groups (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012
Statement of Operations - Discontinued Operations
Income from discontinued operations, net of tax	$ 1,537	$ 9,071
Net Assets Held for Sale
Balance Sheet - Discontinued Operations
Properties and equipment	782,556
Accumulated depreciation, depletion and amortization	(565,754)
Total assets	216,802
Asset retirement obligation	(28,346)
Net assets	188,456
Segment, Discontinued Operations
Statement of Operations - Discontinued Operations
Natural gas, NGL and crude oil sales	10,274	12,811
Sales from natural gas marketing	450	453
Well operations, pipeline income and other	450	566
Disposal Group, Discontinued Operations, Total revenue	11,174	13,830
Production Costs	5,393	7,102
Cost of natural gas marketing	454	401
Depreciation, depletion and amortization	2,258	11,902
Disposal Group Including Discontinued Operation, Other Expenses	495	348
Gain on sale of properties and equipment	0	(20,335)
Disposal Group Total Operating Expense	8,600	(582)
Income (loss) from discontinued operations	2,574	14,412
Provision (benefit) for income taxes	(1,037)	(5,341)
Income from discontinued operations, net of tax	$ 1,537	$ 9,071