Note 6 - Condensed Income Statement of EXCOR and All Other Joint Ventures (Details) - USD ($)		3 Months Ended		9 Months Ended
	Aug. 31, 2018	May 31, 2019	May 31, 2018	May 31, 2019	May 31, 2018
Net sales		$ 27,774,112	$ 31,480,885	$ 86,003,918	$ 90,200,146
Gross profit		12,557,580	14,209,819	38,547,018	40,529,217
Net income		3,797,785	4,540,968	11,412,552	11,753,467
NTIC’s share of equity in income from joint ventures		1,877,410	2,246,066	5,596,788	5,793,391
NTIC’s dividends received from joint ventures	$ 3,822,785	1,795,542	1,168,420		2,941,807
EXCOR [Member]
Net sales		10,933,386	12,219,414	34,895,042	35,450,664
Gross profit		6,129,046	6,823,609	19,118,704	19,315,099
Net income		2,707,342	3,113,660	8,187,467	8,272,237
NTIC’s share of equity in income from joint ventures		1,353,856	1,558,243	4,094,763	4,138,814
NTIC’s dividends received from joint ventures	2,517,450	1,673,700	581,250		1,780,392
All Other [Member]
Net sales		16,840,726	19,261,471	51,108,876	54,749,482
Gross profit		6,428,534	7,386,210	19,428,314	21,214,118
Net income		1,090,443	1,427,308	3,225,085	3,481,230
NTIC’s share of equity in income from joint ventures		523,554	687,823	$ 1,502,025	1,654,577
NTIC’s dividends received from joint ventures	$ 1,305,335	$ 121,842	$ 587,170		$ 1,161,415