Note 6 - Investments in Joint Ventures - Condensed Income Statement of EXCOR and All Other Joint Ventures (Details) - USD ($)	3 Months Ended		9 Months Ended
	May 31, 2023	May 31, 2022	May 31, 2023	May 31, 2022
Net sales	$ 20,969,726	$ 18,964,921	$ 59,193,317	$ 53,906,973
Gross profit	7,689,142	6,242,088	20,445,452	16,929,353
Net income	1,525,596	1,000,167	2,913,086	5,676,773
Northern Technologies International Corporation’s share of equity in income from joint ventures	1,346,658	1,364,597	3,664,793	3,662,178
EXCOR and All Other Joint Venturs [Member]
Northern Technologies International Corporation’s share of equity in income from joint ventures	1,346,658	1,364,597	3,664,793	3,662,178
Northern Technologies International Corporation's dividends received from joint ventures	45,977	252,000	3,510,716	5,723,176
EXCOR [Member]
Northern Technologies International Corporation’s share of equity in income from joint ventures	828,631	824,784	2,376,575	2,324,605
Northern Technologies International Corporation's dividends received from joint ventures	0	0	2,459,500	4,255,200
All Other [Member]
Northern Technologies International Corporation’s share of equity in income from joint ventures	518,027	539,813	1,288,218	1,337,572
Northern Technologies International Corporation's dividends received from joint ventures	45,977	252,000	1,051,216	1,467,976
Equity Method Investment, Nonconsolidated Investee or Group of Investees [Member]
Net sales	26,312,548	26,594,077	76,525,427	78,218,839
Gross profit	10,494,244	10,626,570	30,223,623	31,504,531
Net income	2,692,444	2,714,979	7,308,398	7,344,175
EXCOR [Member]
Net sales	10,735,862	10,397,916	30,590,265	31,010,578
Gross profit	5,085,837	4,990,697	14,539,314	15,118,133
Net income	1,654,151	1,654,389	4,761,608	4,646,123
All Other [Member]
Net sales	15,576,686		45,935,162	47,208,261
Gross profit	5,408,407		15,684,309	16,386,398
Net income	$ 1,038,293		$ 2,546,790	$ 2,698,052
Joint Ventures in France [Member]
Net sales		16,196,160
Gross profit		5,635,873
Net income		$ 1,060,590