Note 7 - Investments in Joint Ventures - Condensed Income Statement of EXCOR and All Other Joint Ventures (Details) - USD ($)		3 Months Ended		9 Months Ended
		May 31, 2022	May 31, 2021	May 31, 2022	May 31, 2021
Net sales		$ 18,964,921	$ 15,418,524	$ 53,906,973	$ 40,980,518
Gross profit		6,242,088	5,265,942	16,929,353	13,982,936
Net income		1,000,167	2,053,916	5,676,773	4,628,890
Northern Technologies International Corporation’s share of equity in income from joint ventures		1,364,597	2,033,536	3,662,178	5,779,260
EXCOR and All Other Joint Venturs [Member]
Northern Technologies International Corporation’s share of equity in income from joint ventures		1,364,597	2,033,536	3,662,178	5,779,260
Northern Technologies International Corporation’s dividends received from joint ventures		252,000	181,952	5,723,176	3,505,455
EXCOR [Member]
Northern Technologies International Corporation’s share of equity in income from joint ventures		824,784	1,039,576	2,324,605	3,182,691
Northern Technologies International Corporation’s dividends received from joint ventures		0	0	4,255,200	1,809,900
All Other [Member]
Northern Technologies International Corporation’s share of equity in income from joint ventures		539,813
Northern Technologies International Corporation’s dividends received from joint ventures		252,000
Joint Ventures in France [Member]
Northern Technologies International Corporation’s share of equity in income from joint ventures	[1]		993,960	1,337,572	2,596,569
Northern Technologies International Corporation’s dividends received from joint ventures	[1]		181,952	1,467,976	1,695,555
Equity Method Investment, Nonconsolidated Investee or Group of Investees [Member]
Net sales		26,594,077	31,959,539	78,218,839	87,795,284
Gross profit		10,626,570	14,280,775	31,504,531	39,802,014
Net income		2,714,979	4,051,518	7,344,175	11,540,949
EXCOR [Member]
Net sales		10,397,916	12,103,263	31,010,578	32,196,843
Gross profit		4,990,697	6,863,786	15,118,133	18,661,980
Net income		1,654,389	2,068,326	4,646,123	6,351,721
All Other [Member]
Net sales		16,196,160
Gross profit		5,635,873
Net income		$ 1,060,590
Joint Ventures in France [Member]
Net sales	[1]		19,856,276	47,208,261	55,598,441
Gross profit	[1]		7,416,989	16,386,398	21,140,034
Net income	[1]		$ 1,983,192	$ 2,698,052	$ 5,189,228

[1] Includes Zerust India since Zerust India was not a consolidated subsidiary of the Company as of August 31, 2021 or May 31, 2021. See Note 3 entitled “Business Combination.”