Note 7 - Investments in Joint Ventures - Condensed Balance Sheet of EXCOR and All Other Joint Ventures (Details) - USD ($)		May 31, 2022	Aug. 31, 2021
Current assets		$ 38,968,265	$ 33,747,089
Total assets		85,185,397	74,370,879
Current liabilities		14,241,487	8,516,196
Noncurrent liabilities		2,268,240	104,102
Joint ventures’ equity		65,222,459	62,368,028
Investments in joint ventures		22,194,433	27,623,768
EXCOR and All Other Joint Venturs [Member]
Investments in joint ventures		22,194,433	27,623,768
Northern Technologies International Corporation’s share of joint ventures’ undistributed earnings		20,844,284	24,702,778
EXCOR [Member]
Investments in joint ventures		12,374,756	15,412,574
Northern Technologies International Corporation’s share of joint ventures’ undistributed earnings		12,343,851	14,697,490
All Other [Member]
Investments in joint ventures		9,819,677
Northern Technologies International Corporation’s share of joint ventures’ undistributed earnings		8,500,433
Joint Ventures in France [Member]
Investments in joint ventures	[1]		12,211,194
Northern Technologies International Corporation’s share of joint ventures’ undistributed earnings	[1]		10,005,288
Equity Method Investment, Nonconsolidated Investee or Group of Investees [Member]
Current assets		55,305,950	69,394,796
Total assets		59,037,744	73,814,402
Current liabilities		13,289,392	16,366,398
Noncurrent liabilities		1,223,185	1,455,524
Joint ventures’ equity		44,601,335	55,992,480
EXCOR [Member]
Current assets		25,677,287	33,886,655
Total assets		27,727,623	36,211,520
Current liabilities		2,978,114	5,386,377
Noncurrent liabilities		0	0
Joint ventures’ equity		24,749,509	30,825,144
All Other [Member]
Current assets		29,628,663
Total assets		31,310,121
Current liabilities		10,311,279
Noncurrent liabilities		1,223,185
Joint ventures’ equity		$ 19,851,826
Joint Ventures in France [Member]
Current assets	[1]		35,508,141
Total assets	[1]		37,602,882
Current liabilities	[1]		10,980,021
Noncurrent liabilities	[1]		1,455,524
Joint ventures’ equity	[1]		$ 25,167,336

[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.”