Joint Venture with Peabody Energy	12 Months Ended
Dec. 31, 2020
Investment In Joint Venture [Abstract]
Joint Venture with Peabody Energy	6. Joint Venture with Peabody Energy On June 18, 2019, the Company entered into a definitive implementation agreement (the “Implementation Agreement”) with Peabody Energy Corporation (“Peabody”), to establish a joint venture that would have combined the respective Powder River Basin and Colorado mining operations of Arch Resources and Peabody. Pursuant to the terms of the Implementation Agreement, the Company would have held a 33.5% economic interest, and Peabody would have held a 66.5% economic interest in the joint venture. On February 26, 2020, the Federal Trade Commission (“FTC”) filed an administrative complaint challenging the proposed joint venture alleging the transaction would eliminate competition between Arch Resources and Peabody, the two major competitors in the market for thermal coal in the Southern Powder River Basin and the two largest coal-mining companies in the United States. The FTC filed a temporary restraining order and preliminary injunction in the U.S. District Court for the Eastern District of Missouri, to maintain the status quo pending an administrative trial on the merits. Between July 14 and July 23, 2020, the U.S. District Court conducted an evidentiary hearing, during which both sides further presented their evidence and arguments. On September 29, 2020, the U.S. District Court upheld the FTC’s decision to block the joint venture. Subsequently, the Company and Peabody jointly terminated the joint venture. The Company incurred expenses of $16.1 million during the year ended December 31, 2020 associated with the regulatory approval process related to the joint venture. Costs of $13.8 million were incurred for the year ended December 31, 2019.

Joint Venture with Peabody Energy

12 Months Ended

Dec. 31, 2020

Investment In Joint Venture [Abstract]

6. Joint Venture with Peabody Energy

On June 18, 2019, the Company entered into a definitive implementation agreement (the “Implementation Agreement”) with Peabody Energy Corporation (“Peabody”), to establish a joint venture that would have combined the respective Powder River Basin and Colorado mining operations of Arch Resources and Peabody. Pursuant to the terms of the Implementation Agreement, the Company would have held a 33.5% economic interest, and Peabody would have held a 66.5% economic interest in the joint venture.

On February 26, 2020, the Federal Trade Commission (“FTC”) filed an administrative complaint challenging the proposed joint venture alleging the transaction would eliminate competition between Arch Resources and Peabody, the two major competitors in the market for thermal coal in the Southern Powder River Basin and the two largest coal-mining companies in the United States. The FTC filed a temporary restraining order and preliminary injunction in the U.S. District Court for the Eastern District of Missouri, to maintain the status quo pending an administrative trial on the merits.

Between July 14 and July 23, 2020, the U.S. District Court conducted an evidentiary hearing, during which both sides further presented their evidence and arguments. On September 29, 2020, the U.S. District Court upheld the FTC’s decision to block the joint venture. Subsequently, the Company and Peabody jointly terminated the joint venture.

The Company incurred expenses of $16.1 million during the year ended December 31, 2020 associated with the regulatory approval process related to the joint venture. Costs of $13.8 million were incurred for the year ended December 31, 2019.