Note 7 - Investments in Joint Ventures - Condensed Income Statement of EXCOR and All Other Joint Ventures (Details) - USD ($)		3 Months Ended		6 Months Ended
		Feb. 28, 2022	Feb. 28, 2021	Feb. 28, 2022	Feb. 28, 2021
Net sales		$ 16,748,639	$ 12,782,882	$ 34,942,052	$ 25,561,994
Gross profit		4,984,335	4,251,203	10,687,265	8,716,994
Net income		182,847	1,312,575	4,676,606	2,574,974
Northern Technologies International Corporation’s share of equity in income from joint ventures		922,832	1,920,012	2,297,581	3,745,724
Equity Method Investment, Nonconsolidated Investee or Group of Investees [Member]
Net sales		24,601,767	29,058,402	51,624,762	55,835,745
Gross profit		9,845,002	13,079,478	20,877,961	25,521,239
Net income		1,851,591	3,838,007	4,629,196	7,489,431
Northern Technologies International Corporation’s share of equity in income from joint ventures		922,832	1,920,012	2,297,581	3,745,724
Northern Technologies International Corporation's dividends received from joint ventures		320,365	2,198,142	5,362,636	3,323,503
EXCOR [Member]
Net sales		9,312,434	10,542,097	20,612,662	20,093,580
Gross profit		4,658,450	6,099,187	10,127,436	11,798,194
Net income		1,170,187	2,262,321	2,991,734	4,283,395
Northern Technologies International Corporation’s share of equity in income from joint ventures		589,048	1,132,578	1,499,821	2,143,115
Northern Technologies International Corporation's dividends received from joint ventures		0	1,809,900	4,255,200	1,809,900
All Other [Member]
Net sales		15,289,334
Gross profit		5,186,553
Net income		681,404
Northern Technologies International Corporation’s share of equity in income from joint ventures		333,784
Northern Technologies International Corporation's dividends received from joint ventures		$ 320,365
Joint Ventures in France [Member]
Net sales	[1]		18,516,306	31,012,100	35,742,165
Gross profit	[1]		6,980,291	10,750,525	13,723,045
Net income	[1]		1,575,686	1,637,462	3,206,036
Northern Technologies International Corporation’s share of equity in income from joint ventures	[1]		787,434	797,760	1,602,609
Northern Technologies International Corporation's dividends received from joint ventures	[1]		$ 388,242	$ 1,107,436	$ 1,513,603

[1] Includes Harita-NTI since Harita-NTI was not a consolidated subsidiary of the Company as of Augut 31, 2021 or November 30, 2020. See Note 3.