Acquisition and Development Agreement and Carry and Earning Agreement	12 Months Ended
Dec. 31, 2011
Acquisition and Development Agreement and Carry and Earning Agreement [Abstract]
Acquisition and Development Agreement and Carry and Earning Agreement	Note 12 - Acquisition and Development Agreement and Carry and Earning Agreement Acquisition and Development Agreement In June 2011, the Company entered into an Acquisition and Development Agreement with Mitsui E&P Texas LP (“Mitsui”), an indirect subsidiary of Mitsui & Co., Ltd (the “Acquisition and Development Agreement”). Pursuant to the Acquisition and Development Agreement, the Company agreed to transfer to Mitsui a 12.5 percent working interest in certain non-operated oil and gas assets representing approximately 39,000 net acres in Dimmit, LaSalle, Maverick, and Webb Counties, Texas. As consideration for the oil and gas interests transferred, Mitsui agreed to pay, or carry, 90 percent of certain drilling and completion costs attributable to the Company's remaining interest in these assets following the closing of the transaction, until Mitsui has expended an aggregate $680.0 million on behalf of the Company. Based on the Company's forecast of the operator's drilling plans, it will take three to four years to fully utilize the carry. The agreement also provided for the conveyance of one-half of the Company’s ownership in related gathering assets in exchange for the reimbursement by Mitsui of 50 percent of costs incurred on those assets by the Company through the closing date. The effective date of the transfer was March 1, 2011, and the transaction closed on December 2, 2011. Mitsui has reimbursed the Company for capital expenditures and other costs, net of revenues, that the Company paid and attributable to the transferred interest during the period between the effective date and the closing date. The Company will apply these reimbursed costs to the remaining ten percent of the Company’s drilling and completion costs for the affected acreage. As of December 31, 2011, the Company received $124.7 million of cash payments from Mitsui that are contractually restricted to be used solely for development operations pursuant to the Acquisition and Development Agreement and accordingly are classified as non-current assets. The Company has recorded a corresponding liability equal to the restricted cash balance. The portion of the liability related to development operations expected to occur within the next year is recorded in accounts payable and accrued expenses within the accompanying balance sheets. The portion of the liability related to development operations expected to occur more than one year in the future is recorded in other noncurrent liabilities within the accompanying balance sheets as of December 31, 2011. There was no net impact on the accompanying consolidated statement of cash flows as restricted cash was offset against the corresponding liability in investing activities. None of the carry had been utilized as of year-end. Legal and commission costs associated with the execution of the arrangement were recorded as other operating expense in the accompanying statements of operations. Carry and Earning Agreement On April 29, 2010, the Company entered into a Carry and Earning Agreement, which effectively provided for a third party to earn 95 percent of SM Energy’s interest in approximately 8,400 net acres in a portion of the Company’s East Texas Haynesville shale acreage, as well as an interest in several wells and five percent of SM Energy’s interest in approximately 23,400 net acres in a separate portion of the Company’s Haynesville acreage in East Texas. In exchange for these interests, the third party invested $91.3 million to fund the drilling and completion costs of horizontal wells in the portion of the leases where the Company retained 95 percent of its interest. The parties now share all costs of operations within the area of joint ownership in accordance with their respective ownership interests

Note 12 - Acquisition and Development Agreement and Carry and Earning Agreement

Acquisition and Development Agreement

In June 2011, the Company entered into an Acquisition and Development Agreement with Mitsui E&P Texas LP (“Mitsui”), an indirect subsidiary of Mitsui & Co., Ltd (the “Acquisition and Development Agreement”). Pursuant to the Acquisition and Development Agreement, the Company agreed to transfer to Mitsui a 12.5 percent working interest in certain non-operated oil and gas assets representing approximately 39,000 net acres in Dimmit, LaSalle, Maverick, and Webb Counties, Texas. As consideration for the oil and gas interests transferred, Mitsui agreed to pay, or carry, 90 percent of certain drilling and completion costs attributable to the Company's remaining interest in these assets following the closing of the transaction, until Mitsui has expended an aggregate $680.0 million on behalf of the Company. Based on the Company's forecast of the operator's drilling plans, it will take three to four years to fully utilize the carry. The agreement also provided for the conveyance of one-half of the Company’s ownership in related gathering assets in exchange for the reimbursement by Mitsui of 50 percent of costs incurred on those assets by the Company through the closing date. The effective date of the transfer was March 1, 2011, and the transaction closed on December 2, 2011. Mitsui has reimbursed the Company for capital expenditures and other costs, net of revenues, that the Company paid and attributable to the transferred interest during the period between the effective date and the closing date. The Company will apply these reimbursed costs to the remaining ten percent of the Company’s drilling and completion costs for the affected acreage.

As of December 31, 2011, the Company received $124.7 million of cash payments from Mitsui that are contractually restricted to be used solely for development operations pursuant to the Acquisition and Development Agreement and accordingly are classified as non-current assets. The Company has recorded a corresponding liability equal to the restricted cash balance. The portion of the liability related to development operations expected to occur within the next year is recorded in accounts payable and accrued expenses within the accompanying balance sheets. The portion of the liability related to development operations expected to occur more than one year in the future is recorded in other noncurrent liabilities within the accompanying balance sheets as of December 31, 2011. There was no net impact on the accompanying consolidated statement of cash flows as restricted cash was offset against the corresponding liability in investing activities. None of the carry had been utilized as of year-end. Legal and commission costs associated with the execution of the arrangement were recorded as other operating expense in the accompanying statements of operations.

Carry and Earning Agreement

On April 29, 2010, the Company entered into a Carry and Earning Agreement, which effectively provided for a third party to earn 95 percent of SM Energy’s interest in approximately 8,400 net acres in a portion of the Company’s East Texas Haynesville shale acreage, as well as an interest in several wells and five percent of SM Energy’s interest in approximately 23,400 net acres in a separate portion of the Company’s Haynesville acreage in East Texas. In exchange for these interests, the third party invested $91.3 million to fund the drilling and completion costs of horizontal wells in the portion of the leases where the Company retained 95 percent of its interest. The parties now share all costs of operations within the area of joint ownership in accordance with their respective ownership interests