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Note 6 - Investments in Joint Ventures (Detail) - Condensed Income Statement of EXCOR and NTI ASEAN, and All Other Joint Ventures: (USD $)
 3 Months Ended
Nov. 30, 2012
Nov. 30, 2011
Net sales $ 27,524,934 $ 28,795,232
Gross profit 13,127,067 13,339,072
Net income 2,440,560 2,538,769
Northern Technologies International Corporation’s share of equity in income of joint ventures 1,154,296 1,357,680
EXCOR [Member]
    
Net sales 8,609,463 8,542,250
Gross profit 4,434,290 4,325,802
Net income 1,570,374 1,457,055
Northern Technologies International Corporation’s share of equity in income of joint ventures 785,187 728,528
China [Member]
    
Net sales 3,568,798  
Gross profit 1,730,402  
Net income 294,003  
Northern Technologies International Corporation’s share of equity in income of joint ventures 147,001  
All Other [Member]
    
Net sales 15,346,673 15,230,654
Gross profit 6,962,375 6,726,565
Net income 576,183 689,348
Northern Technologies International Corporation’s share of equity in income of joint ventures 222,108 259,691
NTI ASEAN [Member]
    
Net sales   5,022,328
Gross profit   2,286,705
Net income   738,922
Northern Technologies International Corporation’s share of equity in income of joint ventures   $ 369,461