Summary of Significant Accounting Policies (Details) (USD $)	12 Months Ended			0 Months Ended	3 Months Ended	12 Months Ended											0 Months Ended
	Dec. 31, 2012 Cogeneration_facilities Industry_Segments counterparty	Dec. 31, 2011	Dec. 31, 2010	Jul. 23, 2010 Flying J	Sep. 30, 2010 Flying J	Dec. 31, 2008 Flying J	Dec. 31, 2012 Minimum Building and Building Improvements	Dec. 31, 2012 Minimum Machinery and Equipment	Dec. 31, 2012 Maximum Building and Building Improvements	Dec. 31, 2012 Maximum Machinery and Equipment	Dec. 31, 2012 Electricity Cost Allocation	Dec. 31, 2011 Electricity Cost Allocation	Dec. 31, 2010 Electricity Cost Allocation	Dec. 31, 2012 Costs of Transporting Natural Gas	Dec. 31, 2011 Costs of Transporting Natural Gas	Dec. 31, 2010 Costs of Transporting Natural Gas	Dec. 31, 2012 Derivative
Accounting Policies
Maximum maturity for cash equivalents	3 months
Bank Overdrafts	$ 14,900,000	$ 16,100,000
Collection period for trade accounts receivable, months	2 months
Asset Retirement Obligation, Current	4,430,000	4,763,000
Concentration Risk, Credit Risk, Financial Instrument, Maximum Exposure																	23,200,000
Derivative Number of Counterparties to Commodity Contracts	9
Allowance for bad debt	414,000	0	0			38,500,000
Litigation settlement, gross				60,500,000
Proceeds received from bankruptcy claim				60,500,000
Settlement of Flying J bankruptcy claim	0	0	21,992,000		22,000,000
Allowance for Doubtful Accounts Receivable, Recoveries	0	0	38,508,000		38,500,000
Property, plant and equipment, useful lives, minimum (in years)							5 years	3 years	30 years	10 years
Costs of Natural Gas Transportation Used in Oil and Gas Production														28,600,000	21,400,000	16,200,000
Cost of Natural Gas Transportation Used in Electricity Generation														3,800,000	5,000,000	4,700,000
Number of companies owned under equity method investments (in ones)	2
Equity method investment, ownership is less than (as a percent)	50.00%
Impairment of oil and natural gas properties	79,000	625,564,000	0
Number of Cogeneration facilities (in ones)	3
Number of industry segments (in ones)	1
Electricity Production Consumed and Included In Oil Production Costs											$ 2,000,000	$ 2,300,000	$ 2,800,000