Impairment	12 Months Ended
Dec. 31, 2015
Asset Impairment Charges [Abstract]
Impairment	Impairment Property, Plant and Equipment As deemed necessary based on events in 2015, 2014 and 2013, the Company analyzed various property, plant and equipment for impairment. Estimated fair values of these assets were determined using a combination of the discounted cash flow method, recent offers from third-party purchasers or prices of comparable assets with consideration of current market conditions. Given the significance of the unobservable nature of a number of the inputs, these are considered Level 3 on the fair value hierarchy discussed in Note 5. Oil and Natural Gas Properties. The Company incurred impairments of $4.5 billion and $164.8 million for the years ended December 31, 2015 and 2014, respectively, due to a full cost ceiling limitations. The impairments recorded in 2015 resulted primarily from the significant decrease in oil prices, and to a lesser extent, natural gas prices, that began in the latter half of 2014 and continued in 2015. The impairment in 2014 resulted from the divestiture of the Gulf Properties, as the present value of future net revenues associated with the Gulf Properties exceeded the associated reduction to the full cost pool. Drilling Assets. During 2015, the Company evaluated certain drilling assets for impairment based on the Company’s plans for their future use. As a result of these evaluations, the Company recorded impairments of $37.6 million for the year ended December 31, 2015. During the fourth quarter of 2015, the Company classified drilling and oilfield services assets having a net book value of approximately $16.0 million, as held for sale, which were included in other current assets in the accompanying consolidated balance sheet at December 31, 2015. See Note 7 for additional discussion of assets held for sale. As a result of the Company’s fulfillment of its drilling obligation with the Permian Trust and the downward trend in oil prices that began in the second half of 2014, demand for the Company’s drilling and oilfield services in the Permian region declined significantly. At December 31, 2014, the Company determined the future use of its drilling and oilfield services assets in this region was limited and recorded an impairment of $24.3 million on these assets. During 2014 and 2013, the Company committed to plans to sell various drilling assets. The net book value of these drilling assets was adjusted to fair value, resulting in impairments of $3.1 million and $11.1 million for the years ended December 31, 2014 and 2013, respectively. The remaining net book value of these assets is included in other current assets in the accompanying consolidated balance sheet at December 31, 2014. Gas Treating Plants and Other Midstream Assets. During 2015, 2014 and 2013, the Company evaluated certain midstream pipe inventory, natural gas compressors, gas treating plants and a CO₂ compressor station for impairment when it was determined that their future use was limited. As a result of these evaluations, the Company recorded impairments of $7.1 million, $0.6 million and $12.2 million during the years ended December 31, 2015, 2014 and 2013, respectively, on these assets to reduce their carrying value to fair value. Other Property, Plant and Equipment. In the fourth quarter of 2015, the Company signed an agreement to sell one of its properties located in downtown Oklahoma City, Oklahoma. Because the net book value of the property exceeded the agreed upon sales price, the Company adjusted the carrying value of the property to the agreed upon sales price, resulting in an impairment of $15.4 million for the year ended December 31, 2015. Additionally the company evaluated certain gathering and compression equipment for impairment when it was determined their future use was limited. As a result of these evaluations, the Company recorded an impairment of $0.7 million for the year ended December 31, 2015. In the second quarter of 2013, the Company committed to a plan to sell a corporate asset. The net book value of the corporate asset was adjusted to fair value, resulting in an impairment of $2.9 million during the year ended December 31, 2013. The corporate asset was sold in the fourth quarter of 2013.

Impairment

Property, Plant and Equipment

As deemed necessary based on events in 2015, 2014 and 2013, the Company analyzed various property, plant and equipment for impairment. Estimated fair values of these assets were determined using a combination of the discounted cash flow method, recent offers from third-party purchasers or prices of comparable assets with consideration of current market conditions. Given the significance of the unobservable nature of a number of the inputs, these are considered Level 3 on the fair value hierarchy discussed in Note 5.

Oil and Natural Gas Properties. The Company incurred impairments of $4.5 billion and $164.8 million for the years ended December 31, 2015 and 2014, respectively, due to a full cost ceiling limitations. The impairments recorded in 2015 resulted primarily from the significant decrease in oil prices, and to a lesser extent, natural gas prices, that began in the latter half of 2014 and continued in 2015. The impairment in 2014 resulted from the divestiture of the Gulf Properties, as the present value of future net revenues associated with the Gulf Properties exceeded the associated reduction to the full cost pool.

Drilling Assets. During 2015, the Company evaluated certain drilling assets for impairment based on the Company’s plans for their future use. As a result of these evaluations, the Company recorded impairments of $37.6 million for the year ended December 31, 2015. During the fourth quarter of 2015, the Company classified drilling and oilfield services assets having a net book value of approximately $16.0 million, as held for sale, which were included in other current assets in the accompanying consolidated balance sheet at December 31, 2015. See Note 7 for additional discussion of assets held for sale.

As a result of the Company’s fulfillment of its drilling obligation with the Permian Trust and the downward trend in oil prices that began in the second half of 2014, demand for the Company’s drilling and oilfield services in the Permian region declined significantly. At December 31, 2014, the Company determined the future use of its drilling and oilfield services assets in this region was limited and recorded an impairment of $24.3 million on these assets.

During 2014 and 2013, the Company committed to plans to sell various drilling assets. The net book value of these drilling assets was adjusted to fair value, resulting in impairments of $3.1 million and $11.1 million for the years ended December 31, 2014 and 2013, respectively. The remaining net book value of these assets is included in other current assets in the accompanying consolidated balance sheet at December 31, 2014.

Gas Treating Plants and Other Midstream Assets. During 2015, 2014 and 2013, the Company evaluated certain midstream pipe inventory, natural gas compressors, gas treating plants and a CO₂ compressor station for impairment when it was determined that their future use was limited. As a result of these evaluations, the Company recorded impairments of $7.1 million, $0.6 million and $12.2 million during the years ended December 31, 2015, 2014 and 2013, respectively, on these assets to reduce their carrying value to fair value.

Other Property, Plant and Equipment. In the fourth quarter of 2015, the Company signed an agreement to sell one of its properties located in downtown Oklahoma City, Oklahoma. Because the net book value of the property exceeded the agreed upon sales price, the Company adjusted the carrying value of the property to the agreed upon sales price, resulting in an impairment of $15.4 million for the year ended December 31, 2015. Additionally the company evaluated certain gathering and compression equipment for impairment when it was determined their future use was limited. As a result of these evaluations, the Company recorded an impairment of $0.7 million for the year ended December 31, 2015.

In the second quarter of 2013, the Company committed to a plan to sell a corporate asset. The net book value of the corporate asset was adjusted to fair value, resulting in an impairment of $2.9 million during the year ended December 31, 2013. The corporate asset was sold in the fourth quarter of 2013.