Derivative Instruments (Details) (USD $)	3 Months Ended								1 Months Ended	0 Months Ended	3 Months Ended
	Mar. 31, 2013 counterparty	Mar. 31, 2012	Mar. 31, 2013 Full 2013 Term Natural Gas	Mar. 31, 2013 Full 2013 Term Crude Oil	Mar. 31, 2013 Full 2014 Term Natural Gas	Mar. 31, 2013 Full 2014 Term Crude Oil	Mar. 31, 2013 Full 2015 Term Natural Gas	Mar. 31, 2013 Full 2015 Term Crude Oil	Mar. 31, 2012 Termination of Derivatives Natural Gas	Mar. 31, 2013 Derivative	Mar. 31, 2013 Commodity Contract Realized And Unrealized Gain Loss On Derivatives Net	Mar. 31, 2012 Commodity Contract Realized And Unrealized Gain Loss On Derivatives Net	Mar. 31, 2013 Commodity Contract Oil And Natural Gas Sales	Mar. 31, 2012 Commodity Contract Oil And Natural Gas Sales	Mar. 31, 2013 Interest Rate Contract Interest Expense	Mar. 31, 2012 Interest Rate Contract Interest Expense
Derivative [Line Items]
(Gain) loss reclassified from AOCL into earnings (amortization of frozen amounts)													$ 0	$ 2,700,000	$ 0	$ (600,000)
Loss recognized in earnings (cash settlements and mark-to-market movements)	737,000	28,481,000									737,000	28,481,000
Concentration Risk, Credit Risk, Financial Instrument, Maximum Exposure										20,800,000
Derivative, Nonmonetary Notional Amount			10,000	19,800	0	21,000	0	3,000	15,000
Loss on Contract Termination									1,900,000
Derivative Number of Counterparties to Commodity Contracts	9
Derivative Number of Counterparties with Net Liability Position	2
Derivative, Net Liability Position, Aggregate Fair Value	$ 800,000
Derivatives Number of Major Counterparties	2
Percentage of Derivative Value Held by Major Counterparties	69.00%