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| **Subsequent Events [Abstract]**              |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                         |
| Subsequent Events [Text Block]                | SUBSEQUENT EVENTSOn October 8, 2013, PDCM executed a purchase and sale agreement with an unrelated third-party pursuant to which PDCM agreed to sell its shallow upper Devonian (non-Marcellus Shale) Appalachian Basin crude oil and natural gas properties for aggregate consideration of approximately $18.8 million, of which our proportionate share is $6.2 million, after pre-closing adjustments. The properties consist of approximately 3,500 gross shallow producing wells, related facilities and associated shallow leasehold acreage, limited to the upper Devonian and shallower formations. The aggregate cash consideration is subject to customary terms and post-closing adjustments and by certain firm transportation obligations that will be assumed by the buyer. Concurrent with the closing of the transaction, our $6.7 million irrevocable standby letter of credit and related obligations will be novated to the buyer. We expect this sale to close in the fourth quarter of 2013. However, there can be no assurance we will be successful in closing this divestiture. |

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| - Definition
The entire disclosure for significant events or transactions that occurred after the balance sheet date through the date the financial statements were issued or the date the financial statements were available to be issued. Examples include: the sale of a capital stock issue, purchase of a business, settlement of litigation, catastrophic loss, significant foreign exchange rate changes, loans to insiders or affiliates, and transactions not in the ordinary course of business.
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No definition available.
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