Assets Held for Sale Assets Held for Sale	6 Months Ended
Jun. 30, 2013
Assets held for sale [Abstract]
Divestitures and Assets Held-for-sale	Note 3 – Assets Held for Sale Assets are classified as held for sale when the Company commits to a plan to sell the assets and there is reasonable certainty the sale will take place within one year. Upon classification as held for sale, long-lived assets are no longer depreciated or depleted, and a measurement for impairment is performed to identify and expense any excess of carrying value over fair value less costs to sell. Subsequent changes to the estimated fair value less the cost to sell will impact the measurement of assets held for sale for which fair value less costs to sell is determined to be less than the carrying value of the assets. As of June 30, 2013, the accompanying condensed consolidated balance sheets (“accompanying balance sheets”) present $87.3 million of assets held for sale, net of accumulated depletion, depreciation, and amortization expense. A corresponding asset retirement obligation liability of $4.6 million is separately presented. The assets held for sale include certain assets located in all four of the Company’s regions, all of which are recorded at the lesser of their carrying values or their respective fair value less estimated costs to sell. Write-downs to fair value less estimated costs to sell are reflected in the gain (loss) on divestiture activity line item in the accompanying condensed consolidated statements of operations (“accompanying statements of operations”). Subsequent to June 30, 2013, the Company began the marketing of certain assets in its Mid-Continent region. The Company expects the marketing of these assets to take approximately six months. These assets were not classified as held for sale as of June 30, 2013. The Company determined that these planned asset sales do not qualify for discontinued operations accounting under financial statement presentation authoritative guidance.

Note 3 – Assets Held for Sale

Assets are classified as held for sale when the Company commits to a plan to sell the assets and there is reasonable certainty the sale will take place within one year. Upon classification as held for sale, long-lived assets are no longer depreciated or depleted, and a measurement for impairment is performed to identify and expense any excess of carrying value over fair value less costs to sell. Subsequent changes to the estimated fair value less the cost to sell will impact the measurement of assets held for sale for which fair value less costs to sell is determined to be less than the carrying value of the assets.

As of June 30, 2013, the accompanying condensed consolidated balance sheets (“accompanying balance sheets”) present $87.3 million of assets held for sale, net of accumulated depletion, depreciation, and amortization expense. A corresponding asset retirement obligation liability of $4.6 million is separately presented. The assets held for sale include certain assets located in all four of the Company’s regions, all of which are recorded at the lesser of their carrying values or their respective fair value less estimated costs to sell. Write-downs to fair value less estimated costs to sell are reflected in the gain (loss) on divestiture activity line item in the accompanying condensed consolidated statements of operations (“accompanying statements of operations”).

Subsequent to June 30, 2013, the Company began the marketing of certain assets in its Mid-Continent region. The Company expects the marketing of these assets to take approximately six months. These assets were not classified as held for sale as of June 30, 2013.

The Company determined that these planned asset sales do not qualify for discontinued operations accounting under financial statement presentation authoritative guidance.