| Cover | Jan. 06, 2022 |
| Cover [Abstract] | |
| Document Type | 8-K |
| Amendment Flag | false |
| Document Period End Date | Jan. 6, 2022 |
| Entity File Number | 001-11038 |
| Entity Registrant Name | NORTHERN TECHNOLOGIES INTERNATIONAL CORPORATION |
| Entity Central Index Key | 0000875582 |
| Entity Tax Identification Number | 41-0857886 |
| Entity Incorporation, State or Country Code | DE |
| Entity Address, Address Line One | 4201 Woodland RoadP.O. Box 69 |
| Entity Address, City or Town | Circle Pines |
| Entity Address, State or Province | MN |
| Entity Address, Postal Zip Code | 55014 |
| City Area Code | 763 |
| Local Phone Number | 225-6600 |
| Written Communications | false |
| Soliciting Material | false |
| Pre-commencement Tender Offer | false |
| Pre-commencement Issuer Tender Offer | false |
| Title of 12(b) Security | Common stock, par value $0.02 per share |
| Trading Symbol | NTIC |
| Security Exchange Name | NASDAQ |
| Entity Emerging Growth Company | false |
