| Document and Entity Information | Oct. 06, 2024 |
| Cover [Abstract] | |
| Amendment Flag | false |
| Entity Central Index Key | 0001304492 |
| Document Type | 8-K |
| Document Period End Date | Oct. 06, 2024 |
| Entity Registrant Name | Anterix Inc. |
| Entity Incorporation State Country Code | DE |
| Entity File Number | 001-36827 |
| 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 |
| Written Communications | false |
| Soliciting Material | false |
| Pre Commencement Tender Offer | false |
| Pre Commencement Issuer Tender Offer | false |
| Security 12b Title | Common Stock, $0.0001 par value |
| Trading Symbol | ATEX |
| Security Exchange Name | NASDAQ |
| Entity Emerging Growth Company | false |
