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Cover - USD ($)
 12 Months Ended
Mar. 31, 2022
May 24, 2022
Sep. 30, 2021
Cover [Abstract]      
Document Type 10-K    
Document Annual Report true    
Document Period End Date Mar. 31, 2022    
Current Fiscal Year End Date --03-31    
Document Transition Report false    
Entity File Number 001-36827    
Entity Registrant Name Anterix Inc.    
Entity Incorporation, State or Country Code DE    
Entity Tax Identification Number 33-0745043    
Entity Address, Address Line One 3 Garret Mountain Plaza    
Entity Address, Address Line Two Suite 401    
Entity Address, City or Town Woodland Park,    
Entity Address, State or Province NJ    
Entity Address, Postal Zip Code 07424    
City Area Code 973    
Local Phone Number 771-0300    
Title of 12(b) Security Common Stock, $0.0001 par value    
Trading Symbol ATEX    
Security Exchange Name NASDAQ    
Entity Well-known Seasoned Issuer No    
Entity Voluntary Filers No    
Entity Current Reporting Status Yes    
Entity Interactive Data Current Yes    
Entity Filer Category Large Accelerated Filer    
Entity Small Business false    
Entity Emerging Growth Company false    
ICFR Auditor Attestation Flag true    
Entity Shell Company false    
Entity Public Float     $ 775,403,925
Entity Common Stock, Shares Outstanding   18,933,986  
Documents Incorporated by Reference Portions of the registrant’s definitive proxy statement to be filed with the Securities and Exchange Commission pursuant to Regulation 14A in connection with the registrant’s 2022 Annual Meeting of Stockholders, which will be filed subsequent to the date hereof, are incorporated by reference into Part III of this Form 10-K where indicated. Such definitive proxy statement will be filed with the Securities and Exchange Commission not later than 120 days following the end of the registrant’s fiscal year ended March 31, 2022.    
Document Fiscal Year Focus 2022    
Document Fiscal Period Focus FY    
Entity Central Index Key 0001304492    
Amendment Flag false