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Document And Entity Information - shares
 9 Months Ended
May 31, 2020
Jul. 09, 2020
Document Information [Line Items]    
Entity Registrant Name Northern Technologies International Corporation  
Entity Central Index Key 0000875582  
Trading Symbol ntic  
Current Fiscal Year End Date --08-31  
Entity Filer Category Accelerated Filer  
Entity Current Reporting Status Yes  
Entity Emerging Growth Company false  
Entity Small Business true  
Entity Interactive Data Current Yes  
Entity Common Stock, Shares Outstanding (in shares)   9,099,990
Entity Shell Company false  
Document Type 10-Q  
Document Period End Date May 31, 2020  
Document Fiscal Year Focus 2020  
Document Fiscal Period Focus Q3  
Amendment Flag false  
Title of 12(b) Security Common stock, par value $0.02 per share