Note 7 - Investments in Joint Ventures (Details) - Condensed Balance Sheet of EXCOR and NTI ASEAN, and All Other Joint Ventures (USD $)	Aug. 31, 2013	Aug. 31, 2012
Condensed Balance Sheet Statements, Captions [Line Items]
Current assets	$ 63,052,410	$ 61,973,725
Total assets	68,417,142	68,585,974
Current liabilities	16,107,597	18,686,181
Noncurrent liabilities	2,488,057	4,700,458
Joint ventures’ equity	49,821,488	45,199,335
Northern Technologies International Corporation’s share of joint ventures’ equity	24,702,981	21,461,492
Northern Technologies International Corporation's share of joint ventures' undistributed earnings	22,281,510	19,403,150
EXCOR [Member]
Condensed Balance Sheet Statements, Captions [Line Items]
Current assets	25,955,136	24,357,139
Total assets	28,391,787	26,620,589
Current liabilities	3,572,004	4,749,574
Joint ventures’ equity	24,819,783	21,871,015
Northern Technologies International Corporation’s share of joint ventures’ equity	12,409,893	10,935,509
Northern Technologies International Corporation's share of joint ventures' undistributed earnings	12,378,988	10,904,604
China [Member]
Condensed Balance Sheet Statements, Captions [Line Items]
Current assets	11,200,355
Total assets	11,226,755
Current liabilities	3,080,118
Noncurrent liabilities	871,886
Joint ventures’ equity	7,274,751
Northern Technologies International Corporation’s share of joint ventures’ equity	3,637,375
Northern Technologies International Corporation's share of joint ventures' undistributed earnings	3,587,375
All Other [Member]
Condensed Balance Sheet Statements, Captions [Line Items]
Current assets	25,896,919	22,257,619
Total assets	28,798,600	26,442,929
Current liabilities	9,455,475	8,172,750
Noncurrent liabilities	1,616,171	3,644,493
Joint ventures’ equity	17,726,954	14,625,686
Northern Technologies International Corporation’s share of joint ventures’ equity	8,655,713	6,840,579
Northern Technologies International Corporation's share of joint ventures' undistributed earnings	6,315,147	5,184,101
NTI ASEAN [Member]
Condensed Balance Sheet Statements, Captions [Line Items]
Current assets		15,358,967
Total assets		15,522,456
Current liabilities		5,763,857
Noncurrent liabilities		1,055,965
Joint ventures’ equity		8,702,634
Northern Technologies International Corporation’s share of joint ventures’ equity		3,685,404
Northern Technologies International Corporation's share of joint ventures' undistributed earnings		$ 3,314,445