Note 6 - Investments in Joint Ventures - Condensed Balance Sheet of EXCOR and All Other Joint Ventures (Details) - USD ($)	Feb. 28, 2021	Aug. 31, 2020
Current assets	$ 37,522,588	$ 33,202,350
Total assets	71,116,169	66,074,488
Current liabilities	8,051,249	6,097,604
Noncurrent liabilities	369,956	272,443
Joint ventures’ equity	59,462,158	56,659,415
Investments in joint ventures	24,860,148	24,090,826
Equity Method Investment, Nonconsolidated Investee or Group of Investees [Member]
Current assets	61,766,682	55,825,418
Total assets	65,973,432	60,295,587
Current liabilities	15,175,228	11,002,867
Noncurrent liabilities	332,479	365,274
Joint ventures’ equity	50,465,725	48,927,446
Investments in joint ventures	24,860,148	24,090,826
Northern Technologies International Corporation’s share of joint ventures’ undistributed earnings	22,625,070	21,855,747
EXCOR [Member]
Current assets	27,772,018	25,742,619
Total assets	30,256,723	28,449,772
Current liabilities	3,268,087	2,424,565
Noncurrent liabilities	0	0
Joint ventures’ equity	26,988,636	26,025,207
Investments in joint ventures	13,494,320	13,012,606
Northern Technologies International Corporation’s share of joint ventures’ undistributed earnings	13,463,415	12,981,701
All Other [Member]
Current assets	33,994,664	30,082,799
Total assets	35,716,709	31,845,815
Current liabilities	11,907,141	8,578,302
Noncurrent liabilities	332,479	365,274
Joint ventures’ equity	23,477,089	22,902,239
Investments in joint ventures	11,365,828	11,078,220
Northern Technologies International Corporation’s share of joint ventures’ undistributed earnings	$ 9,161,655	$ 8,874,046