Note 6 - Investments in Joint Ventures (Detail) - Condensed Balance Sheet of EXCOR and NTI ASEAN, and All Other Joint Ventures: (USD $)	Aug. 31, 2012	Aug. 31, 2011
Current assets	$ 61,973,725	$ 66,956,061
Total assets	68,585,974	73,155,916
Current liabilities	18,686,181	24,712,555
Noncurrent liabilities	4,700,458	4,605,837
Joint ventures’ equity	45,199,335	43,752,524
Northern Technologies International Corporation’s share of joint ventures’ equity	21,461,492	20,559,509
Northern Technologies International Corporation's share of joint ventures' undistributed earnings	19,403,150	18,967,125
EXCOR [Member]
Current assets	24,357,139	24,411,880
Total assets	26,620,589	27,093,874
Current liabilities	4,749,574	5,145,239
Joint ventures’ equity	21,871,015	21,948,635
Northern Technologies International Corporation’s share of joint ventures’ equity	10,935,509	10,931,819
Northern Technologies International Corporation's share of joint ventures' undistributed earnings	10,904,604	10,900,914
NTI ASEAN [Member]
Current assets	15,358,967	14,565,219
Total assets	15,522,456	14,759,582
Current liabilities	5,763,857	6,123,684
Noncurrent liabilities	1,055,965	1,020,034
Joint ventures’ equity	8,702,634	7,615,864
Northern Technologies International Corporation’s share of joint ventures’ equity	3,685,404	2,803,194
Northern Technologies International Corporation's share of joint ventures' undistributed earnings	3,314,445	2,432,235
All Other [Member]
Current assets	22,257,619	27,978,962
Total assets	26,442,929	31,302,460
Current liabilities	8,172,750	13,443,632
Noncurrent liabilities	3,644,493	3,585,803
Joint ventures’ equity	14,625,686	14,273,025
Northern Technologies International Corporation’s share of joint ventures’ equity	6,840,579	6,824,496
Northern Technologies International Corporation's share of joint ventures' undistributed earnings	$ 5,184,101	$ 5,633,976