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Cover
Oct. 05, 2020
Cover [Abstract]  
Document Type 8-K
Amendment Flag false
Document Period End Date Oct. 05, 2020
Entity File Number 1-13105
Entity Registrant Name Arch Resources, Inc.
Entity Central Index Key 0001037676
Entity Tax Identification Number 43-0921172
Entity Incorporation, State or Country Code DE
Entity Address, Address Line One CityPlace One
Entity Address, Address Line Two One CityPlace Drive, Suite 300
Entity Address, City or Town St. Louis
Entity Address, State or Province MO
Entity Address, Postal Zip Code 63141
City Area Code 314
Local Phone Number 994-2700
Written Communications false
Soliciting Material false
Pre-commencement Tender Offer false
Pre-commencement Issuer Tender Offer false
Title of 12(b) Security Common Stock, $.01 par value
Trading Symbol ARCH
Security Exchange Name NYSE
Entity Emerging Growth Company false