Impairment	6 Months Ended
Jun. 30, 2012
Impairment [Abstract]
Impairment	Impairment The Company reviews its long-lived assets for impairment, including oil and gas properties, whenever events or circumstances indicate their carrying values may not be fully recoverable. During the past year, reductions in management's outlook for commodity prices have provided indications of possible impairment of the Company's predominately dry gas properties in the Edwards Trend and Austin Chalk fields in South Texas, the Barnett Shale field in North Texas and the Raton field in Southeastern Colorado. As a result of management's assessments, during the fourth quarter of 2011 and second quarter of 2012, the Company recognized pretax noncash impairment charges of $354.4 million and $444.9 million, respectively, to reduce the carrying value of the Edwards Trend/Austin Chalk fields and the Barnett Shale field to their estimated fair values. The Company calculated the estimated fair value of the Barnett Shale field as of June 30, 2012 using a discounted cash flow model. Significant Level 3 assumptions associated with the calculation of discounted cash flows include management's outlook for (i) oil and gas prices of $87.09 per BBL for oil and $4.64 per MCF of gas, (ii) production costs, (iii) capital expenditures and (iv) production and estimated proved reserves and risk-adjusted probable reserves. Management's commodity price outlooks represent longer-term outlooks that are developed based on third-party futures price outlooks as of a measurement date. The expected future net cash flows were discounted using an annual rate of 10 percent to determine estimated fair value. Impairment risk. The Company's estimates of undiscounted future net cash flows attributable to the Raton field's gas properties indicated on June 30, 2012 that its carrying amount was expected to be recovered. However, the carrying value of this field continues to be at risk for impairment if future estimates of undiscounted cash flows decline. As of June 30, 2012, the Company's Raton field has a carrying value of $2.3 billion. It is reasonably possible that the estimate of undiscounted future net cash flows attributable to this or other properties may change in the future resulting in the need to impair their carrying values. The primary factors that may affect estimates of futures cash flows are (i) future reserve adjustments, both positive and negative, to proved reserves and appropriate risk-adjusted probable and possible reserves, (ii) results of future drilling activities, (iii) management's commodity price outlooks and (iv) increases or decreases in production and capital costs associated with the fields.

Impairment

The Company reviews its long-lived assets for impairment, including oil and gas properties, whenever events or circumstances indicate their carrying values may not be fully recoverable. During the past year, reductions in management's outlook for commodity prices have provided indications of possible impairment of the Company's predominately dry gas properties in the Edwards Trend and Austin Chalk fields in South Texas, the Barnett Shale field in North Texas and the Raton field in Southeastern Colorado. As a result of management's assessments, during the fourth quarter of 2011 and second quarter of 2012, the Company recognized pretax noncash impairment charges of $354.4 million and $444.9 million, respectively, to reduce the carrying value of the Edwards Trend/Austin Chalk fields and the Barnett Shale field to their estimated fair values. The Company calculated the estimated fair value of the Barnett Shale field as of June 30, 2012 using a discounted cash flow model. Significant Level 3 assumptions associated with the calculation of discounted cash flows include management's outlook for (i) oil and gas prices of $87.09 per BBL for oil and $4.64 per MCF of gas, (ii) production costs, (iii) capital expenditures and (iv) production and estimated proved reserves and risk-adjusted probable reserves. Management's commodity price outlooks represent longer-term outlooks that are developed based on third-party futures price outlooks as of a measurement date. The expected future net cash flows were discounted using an annual rate of 10 percent to determine estimated fair value.

Impairment risk. The Company's estimates of undiscounted future net cash flows attributable to the Raton field's gas properties indicated on June 30, 2012 that its carrying amount was expected to be recovered. However, the carrying value of this field continues to be at risk for impairment if future estimates of undiscounted cash flows decline. As of June 30, 2012, the Company's Raton field has a carrying value of $2.3 billion.

It is reasonably possible that the estimate of undiscounted future net cash flows attributable to this or other properties may change in the future resulting in the need to impair their carrying values. The primary factors that may affect estimates of futures cash flows are (i) future reserve adjustments, both positive and negative, to proved reserves and appropriate risk-adjusted probable and possible reserves, (ii) results of future drilling activities, (iii) management's commodity price outlooks and (iv) increases or decreases in production and capital costs associated with the fields.