Note 6 - Investments in Joint Ventures - Condensed Balance Sheet of EXCOR and All Other Joint Ventures (Details) - USD ($)	Aug. 31, 2021	Aug. 31, 2020
Current assets	$ 33,747,089	$ 33,202,350
Total assets	74,370,879	66,074,488
Current liabilities	8,516,196	6,097,604
Noncurrent liabilities	104,102	272,443
Joint ventures’ equity	62,368,026	56,659,415
Investments in joint ventures	27,623,768	24,090,826
Equity Method Investment, Nonconsolidated Investee or Group of Investees [Member]
Current assets	69,394,796	55,825,418
Total assets	73,814,402	60,295,587
Current liabilities	16,366,398	11,002,867
Noncurrent liabilities	1,455,524	365,274
Joint ventures’ equity	55,992,480	48,927,446
Investments in joint ventures	27,623,768	24,090,826
Northern Technologies International Corporation’s share of joint ventures’ undistributed earnings	24,702,778	21,855,747
EXCOR [Member]
Current assets	33,886,655	25,742,619
Total assets	36,211,520	28,449,772
Current liabilities	5,386,377	2,424,565
Noncurrent liabilities	0	0
Joint ventures’ equity	30,825,144	26,025,207
Investments in joint ventures	15,412,574	13,012,606
Northern Technologies International Corporation’s share of joint ventures’ undistributed earnings	14,697,490	12,981,701
All Other [Member]
Current assets	35,508,141	15,994,506
Total assets	37,602,882	16,413,073
Current liabilities	10,980,021	4,088,235
Noncurrent liabilities	1,455,524	332,275
Joint ventures’ equity	25,167,336	11,992,563
Investments in joint ventures	12,211,194	5,621,446
Northern Technologies International Corporation’s share of joint ventures’ undistributed earnings	$ 10,005,288	4,404,094
Joint Ventures in France [Member]
Current assets		4,099,160
Total assets		4,873,484
Current liabilities		2,073,710
Noncurrent liabilities		0
Joint ventures’ equity		2,799,774
Investments in joint ventures		1,399,887
Northern Technologies International Corporation’s share of joint ventures’ undistributed earnings		1,399,887
Joint Ventures in Finland [Member]
Current assets		1,955,879
Total assets		2,261,147
Current liabilities		415,496
Noncurrent liabilities		0
Joint ventures’ equity		1,845,651
Investments in joint ventures		922,814
Northern Technologies International Corporation’s share of joint ventures’ undistributed earnings		902,814
Joint Ventures in India [Member]
Current assets		4,010,855
Total assets		4,242,660
Current liabilities		1,007,529
Noncurrent liabilities		32,999
Joint ventures’ equity		3,202,132
Investments in joint ventures		1,603,013
Northern Technologies International Corporation’s share of joint ventures’ undistributed earnings		738,191
Joint Ventures in Thailand [Member]
Current assets		4,022,399
Total assets		4,055,451
Current liabilities		993,332
Noncurrent liabilities		0
Joint ventures’ equity		3,062,119
Investments in joint ventures		1,531,060
Northern Technologies International Corporation’s share of joint ventures’ undistributed earnings		$ 1,429,060