Note 7 - Investments in Joint Ventures - Condensed Income Statement of EXCOR and All Other Joint Ventures (Details) - USD ($)
 3 Months Ended 9 Months Ended
May 31, 2022
May 31, 2021
May 31, 2022
May 31, 2021
Net sales $ 18,964,921 $ 15,418,524 $ 53,906,973 $ 40,980,518
Gross profit 6,242,088 5,265,942 16,929,353 13,982,936
Net income 1,000,167 2,053,916 5,676,773 4,628,890
Northern Technologies International Corporation’s share of equity in income from joint ventures 1,364,597 2,033,536 3,662,178 5,779,260
EXCOR and All Other Joint Venturs [Member]        
Northern Technologies International Corporation’s share of equity in income from joint ventures 1,364,597 2,033,536 3,662,178 5,779,260
Northern Technologies International Corporation’s dividends received from joint ventures 252,000 181,952 5,723,176 3,505,455
EXCOR [Member]        
Northern Technologies International Corporation’s share of equity in income from joint ventures 824,784 1,039,576 2,324,605 3,182,691
Northern Technologies International Corporation’s dividends received from joint ventures 0 0 4,255,200 1,809,900
All Other [Member]        
Northern Technologies International Corporation’s share of equity in income from joint ventures 539,813      
Northern Technologies International Corporation’s dividends received from joint ventures 252,000      
Joint Ventures in France [Member]        
Northern Technologies International Corporation’s share of equity in income from joint ventures [1]   993,960 1,337,572 2,596,569
Northern Technologies International Corporation’s dividends received from joint ventures [1]   181,952 1,467,976 1,695,555
Equity Method Investment, Nonconsolidated Investee or Group of Investees [Member]        
Net sales 26,594,077 31,959,539 78,218,839 87,795,284
Gross profit 10,626,570 14,280,775 31,504,531 39,802,014
Net income 2,714,979 4,051,518 7,344,175 11,540,949
EXCOR [Member]        
Net sales 10,397,916 12,103,263 31,010,578 32,196,843
Gross profit 4,990,697 6,863,786 15,118,133 18,661,980
Net income 1,654,389 2,068,326 4,646,123 6,351,721
All Other [Member]        
Net sales 16,196,160      
Gross profit 5,635,873      
Net income $ 1,060,590      
Joint Ventures in France [Member]        
Net sales [1]   19,856,276 47,208,261 55,598,441
Gross profit [1]   7,416,989 16,386,398 21,140,034
Net income [1]   $ 1,983,192 $ 2,698,052 $ 5,189,228
[1] Includes Zerust India since Zerust India was not a consolidated subsidiary of the Company as of August 31, 2021 or May 31, 2021. See Note 3 entitled “Business Combination.”