Note 6 - Condensed Income Statement of EXCOR and All Other Joint Ventures (Details) - USD ($)	12 Months Ended
	Aug. 31, 2016	Aug. 31, 2015
EXCOR [Member]
Net sales	$ 35,138,214	$ 36,872,664
Gross profit	18,635,421	19,993,763
Net income	7,049,462	8,201,659
Northern Technologies International Corporation’s share of equity in income from joint ventures	3,534,113	4,091,608
All Other [Member]
Net sales	55,508,619	62,153,587
Gross profit	21,805,305	28,403,555
Net income	2,485,309	3,647,448
Northern Technologies International Corporation’s share of equity in income from joint ventures	1,209,718	1,844,957
Net sales	90,646,833	99,026,251
Gross profit	40,440,726	48,397,318
Net income	9,534,771	11,849,107
Northern Technologies International Corporation’s share of equity in income from joint ventures	$ 4,743,831	$ 5,936,565