Note 6 - Investments in Joint Ventures (Details) - Condensed Balance Sheet of EXCOR and Tianjin Zerust, and All Other Joint Ventures (USD $)	Feb. 28, 2015	Aug. 31, 2014
Condensed Balance Sheet Statements, Captions [Line Items]
Current assets	$ 46,802,727	$ 61,491,957
Total assets	50,375,058	65,466,964
Current liabilities	12,347,251	17,542,634
Noncurrent liabilities	1,080,425	1,929,488
Joint ventures’ equity	36,947,382	45,994,842
Northern Technologies International Corporation’s share of joint ventures’ equity	18,377,038	22,961,989
Northern Technologies International Corporation’s share of joint ventures’ undistributed earnings	16,252,890	20,540,523
EXCOR [Member]
Condensed Balance Sheet Statements, Captions [Line Items]
Current assets	19,669,250	24,361,157
Total assets	21,662,648	26,652,165
Current liabilities	2,837,566	3,512,143
Joint ventures’ equity	18,825,082	23,140,022
Northern Technologies International Corporation’s share of joint ventures’ equity	9,412,543	11,570,013
Northern Technologies International Corporation’s share of joint ventures’ undistributed earnings	9,381,638	11,539,108
All Other [Member]
Condensed Balance Sheet Statements, Captions [Line Items]
Current assets	27,133,477	27,356,120
Total assets	28,712,410	29,020,996
Current liabilities	9,509,685	9,592,111
Noncurrent liabilities	1,080,425	1,061,111
Joint ventures’ equity	18,122,300	18,367,775
Northern Technologies International Corporation’s share of joint ventures’ equity	8,964,499	9,148,452
Northern Technologies International Corporation’s share of joint ventures’ undistributed earnings	6,871,252	6,807,891
Tianjin Zerust [Member]
Condensed Balance Sheet Statements, Captions [Line Items]
Current assets		9,774,680
Total assets		9,793,803
Current liabilities		4,438,380
Noncurrent liabilities		868,377
Joint ventures’ equity		4,487,046
Northern Technologies International Corporation’s share of joint ventures’ equity		2,243,524
Northern Technologies International Corporation’s share of joint ventures’ undistributed earnings		$ 2,193,524

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