Note 7 - Investments in Joint Ventures (Details) - Condensed Income Statement of EXCOR and NTI ASEAN, and All Other Joint Ventures: (USD $)	12 Months Ended
	Aug. 31, 2013	Aug. 31, 2012
Condensed Income Statements, Captions [Line Items]
Net sales	$ 113,189,068	$ 111,830,961
Gross profit	52,058,609	50,679,875
Net income	10,650,542	11,987,323
Northern Technologies International Corporation’s share of equity in income of joint ventures	5,237,711	5,519,795
EXCOR [Member]
Condensed Income Statements, Captions [Line Items]
Net sales	36,476,544	36,027,979
Gross profit	19,470,322	18,667,848
Net income	7,009,897	6,656,298
Northern Technologies International Corporation’s share of equity in income of joint ventures	3,507,057	3,318,213
China [Member]
Condensed Income Statements, Captions [Line Items]
Net sales	15,161,289
Gross profit	7,153,395
Net income	1,157,995
Northern Technologies International Corporation’s share of equity in income of joint ventures	579,376
All Other [Member]
Condensed Income Statements, Captions [Line Items]
Net sales	61,551,235	53,767,947
Gross profit	25,434,891	22,390,097
Net income	2,482,650	1,745,549
Northern Technologies International Corporation’s share of equity in income of joint ventures	1,151,278	787,333
NTI ASEAN [Member]
Condensed Income Statements, Captions [Line Items]
Net sales		22,035,035
Gross profit		9,621,930
Net income		3,585,476
Northern Technologies International Corporation’s share of equity in income of joint ventures		$ 1,414,248