| **Impact of Derivative Instruments on Statement of Operations (Details) (USD $)In Thousands, unless otherwise specified** | 3 Months Ended |
|---------------------------------------------------------------------------------------------------------------------------|----------------|
||
| Commodity Price Risk Management (loss), net                                                                               |           |   |
| **Derivative [Line Items]**                                                                                               |           |   |
| Net settlements                                                                                                           | $ (8,240)      | $ 8,474 |
| Net change in fair value of unsettled derivatives                                                                         | (18,915)       | (30,829) |
| Total commodity price risk management loss, net                                                                           | (27,155)       | (22,355) |
| Sales From Natural Gas Marketing                                                                                          |           |   |
| **Derivative [Line Items]**                                                                                               |           |   |
| Net settlements                                                                                                           | (476)          | 201 |
| Net change in fair value of unsettled derivatives                                                                         | (312)          | (968) |
| Total commodity price risk management loss, net                                                                           | (788)          | (767) |
| Cost of Natural Gas Marketing                                                                                             |           |   |
| **Derivative [Line Items]**                                                                                               |           |   |
| Net settlements                                                                                                           | 535            | (162) |
| Net change in fair value of unsettled derivatives                                                                         | 296            | 1,076 |
| Total commodity price risk management loss, net                                                                           | $ 831          | $ 914 |

| X                                                                                                                                                                                                                                                                                                  |
|----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
The amount of cash received during the period on settlement of a hedge.
+ References
No definition available.
+ Details**Name:**us-gaap_DerivativeCashReceivedOnHedge**Namespace Prefix:**us-gaap_**Data Type:**xbrli:monetaryItemType**Balance Type:**credit**Period Type:**duration |
| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                   |
|-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Amount of realized and unrealized gain (loss) of derivative instruments not designated or qualifying as hedging instruments.
+ References
Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 815 -SubTopic 10 -Section 50 -Paragraph 4C -Subparagraph (e) -URI http://asc.fasb.org/extlink&oid=7476318&loc=SL5624171-113959
+ Details**Name:**us-gaap_DerivativeInstrumentsNotDesignatedAsHedgingInstrumentsGainLossNet**Namespace Prefix:**us-gaap_**Data Type:**xbrli:monetaryItemType**Balance Type:**credit**Period Type:**duration |
| X                                                                                                                                                       |
|---------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Details**Name:**us-gaap_DerivativeLineItems**Namespace Prefix:**us-gaap_**Data Type:**xbrli:stringItemType**Balance Type:**na**Period Type:**duration |
| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                          |
|------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
The net change in the difference between the fair value and the carrying value, or in the comparative fair values, of derivative instruments, including options, swaps, futures, and forward contracts, held at each balance sheet date, that was included in earnings for the period.
+ References
Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 45 -Paragraph 28 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=31042434&loc=d3e3602-108585
+ Details**Name:**us-gaap_UnrealizedGainLossOnDerivatives**Namespace Prefix:**us-gaap_**Data Type:**xbrli:monetaryItemType**Balance Type:**credit**Period Type:**duration |