Annual report pursuant to Section 13 and 15(d)

Cover Page

Cover Page - USD ($)
$ in Millions
12 Months Ended
Dec. 31, 2021
Mar. 04, 2022
Jun. 30, 2021
Document Information [Line Items]      
Document Type 10-K    
Document Annual Report true    
Document Period End Date Dec. 31, 2021    
Current Fiscal Year End Date --12-31    
Document Transition Report false    
Entity File Number 001-39644    
Entity Registrant Name Archaea Energy Inc.    
Entity Incorporation, State or Country Code DE    
Entity Tax Identification Number 85-2867266    
Entity Address, Address Line One 4444 Westheimer Road    
Entity Address, Address Line Two Suite G450    
Entity Address, City or Town Houston    
Entity Address, State or Province TX    
Entity Address, Postal Zip Code 77027    
City Area Code 346    
Local Phone Number 708-8272    
Title of 12(b) Security Class A Common Stock, par value $0.0001 per share    
Trading Symbol LFG    
Security Exchange Name NYSE    
Entity Well-known Seasoned Issuer No    
Entity Voluntary Filers No    
Entity Current Reporting Status Yes    
Entity Interactive Data Current Yes    
Entity Filer Category Non-accelerated Filer    
Entity Small Business true    
Entity Emerging Growth Company true    
Entity Ex Transition Period false    
ICFR Auditor Attestation Flag false    
Entity Shell Company false    
Entity Public Float     $ 433.8
Documents Incorporated by Reference Portions of the registrant’s definitive proxy statement for the 2022 Annual Meeting of Stockholders, to be filed no later than 120 days after the end of the fiscal year to which this Annual Report on Form 10-K relates, are incorporated by reference into Part III of this Annual Report on Form 10-K.    
Amendment Flag false    
Document Fiscal Period Focus FY    
Document Fiscal Year Focus 2021    
Entity Central Index Key 0001823766    
Class A Units      
Document Information [Line Items]      
Entity Common Stock, Shares Outstanding   65,247,198  
Class B Units      
Document Information [Line Items]      
Entity Common Stock, Shares Outstanding   54,224,378