Equity Method Investments and Joint Ventures Disclosure [Text Block]

INVESTMENTS IN JOINT VENTURES

The consolidated financial statements of the Company’s foreign joint ventures are initially prepared using the accounting principles accepted in the respective joint ventures’ countries of domicile. Amounts related to foreign joint ventures reported in the below tables and the accompanying consolidated financial statements have subsequently been adjusted to conform with U.S. GAAP in all material respects. All material profits recorded that remain on the balance sheet on sales from the Company to its joint ventures and from joint ventures to other joint ventures have been eliminated for financial reporting purposes.

Financial information from the audited and unaudited financial statements of the Company’s joint venture in Germany, Excor Korrosionsschutz – Technologien und Produkte GmbH (EXCOR) and all the Company’s other joint ventures, are summarized as follows:

	As of February 28, 2018
	Total		EXCOR		All Other
Current assets	$	57,427,392	$	25,206,550	$	32,220,842
Total assets		61,497,315		27,326,727		34,170,588
Current liabilities		16,468,617		4,148,371		12,320,246
Noncurrent liabilities		120,481		—		120,481
Joint ventures’ equity		44,908,217		23,178,356		21,729,861
Northern Technologies International Corporation’s share of joint ventures’ equity		22,259,526		11,589,180		10,670,346
Northern Technologies International Corporation’s share of joint ventures’ undistributed earnings	$	20,230,286	$	11,558,275	$	8,672,011
Northern Technologies International Corporation’s dividends received from joint ventures	$	1,770,116	$	1,199,142	$	570,974

	Three Months Ended February 28, 2018
	Total		EXCOR		All Other
Net sales	$	30,220,550	$	12,204,736	$	18,015,814
Gross profit		13,531,276		6,557,964		6,973,312
Net income		3,712,684		2,674,777		1,037,907
Northern Technologies International Corporation’s share of equity in income from joint ventures	$	1,805,997	$	1,338,671	$	467,326

	Six Months Ended February 28, 2018
	Total		EXCOR		All Other
Net sales	$	58,719,261	$	23,231,250	$	35,488,011
Gross profit		26,319,398		12,491,490		13,827,908
Net income		7,212,499		5,158,577		2,053,922
Northern Technologies International Corporation’s share of equity in income from joint ventures	$	3,547,325	$	2,580,571	$	966,754

	As of August 31, 2017
	Total		EXCOR		All Other
Current assets	$	51,518,210	$	22,142,514	$	29,375,696
Total assets		55,633,891		24,301,194		31,332,697
Current liabilities		15,118,074		4,469,567		10,648,507
Noncurrent liabilities		181,210		—		181,210
Joint ventures’ equity		40,334,607		19,831,627		20,502,980
Northern Technologies International Corporation’s share of joint ventures’ equity		20,035,074		9,915,816		10,119,258
Northern Technologies International Corporation’s share of joint ventures’ undistributed earnings		17,960,860		9,884,911		8,075,949
Northern Technologies International Corporation’s dividends received from joint ventures	$	6,377,054	$	5,379,062	$	997,992

	Three Months Ended February 28, 2017
	Total		EXCOR		All Other
Net sales	$	22,962,599	$	9,076,908	$	13,885,691
Gross profit		10,161,509		4,867,517		5,293,992
Net income		2,774,943		2,161,408		613,535
Northern Technologies International Corporation’s share of equity in income from joint ventures	$	1,383,139	$	1,078,272	$	304,867

	Six Months Ended February 28, 2017
	Total		EXCOR		All Other
Net sales	$	47,163,046	$	18,285,432	$	28,877,614
Gross profit		20,858,536		9,761,696		11,096,840
Net income		5,182,951		4,017,746		1,165,205
Northern Technologies International Corporation’s share of equity in income from joint ventures	$	2,657,143	$	2,006,441	$	650,702

The Company did

not

make any joint venture investments during the

six

months ended

February 28, 2018

2017.

Note 7 - Corporate Debt	6 Months Ended
Note 7 - Corporate Debt	Feb. 28, 2018
Notes to Financial Statements
Debt Disclosure [Text Block]	7. CORPORATE DEBT The Company has a revolving line of credit with PNC Bank, National Association (PNC Bank) of $3,000,000. No amounts were outstanding under the line of credit as of both February 28, 2018 and August 31, 2017. At the option of the Company, outstanding advances under the line of credit bear interest at either (a) an annual rate based on LIBOR plus 2.15% for the applicable LIBOR interest period selected by the Company or (b) at the rate publicly announced by PNC Bank from time to time as its prime rate. The line of credit is governed under a loan agreement. The loan agreement contains standard covenants, including affirmative financial covenants, such as the maintenance of a minimum fixed charge coverage ratio, and negative covenants, which, among other things, limit the incurrence of additional indebtedness, loans and equity investments, disposition of assets, mergers and consolidations and other matters customarily restricted in such agreements. Under the loan agreement, the Company is subject to a minimum fixed charge coverage ratio of 1.10:1.00. As of February 28, 2018, the Company was in compliance with all debt covenants. The revolving credit facility allows the Company to request that PNC Bank issue letters of credit up to $1,200,000. The Company did not have any letters of credit reserved against the available letters of credit balance as of February 28, 2018 and August 31, 2017 with PNC Bank. The availability of advances under the line of credit will be reduced by the face amount of any letter of credit issued and outstanding (whether or not drawn) under the revolving credit facility. As of February 28, 2018 and August 31, 2017, the Company had $88,831 and $89,543, respectively, of letters of credit with JP Morgan Chase Bank that are performance based and set to expire between 2020 and 2022. On January 5, 2018, the Company and PNC Bank extended the maturity date of the line of credit to January 7, 2019. All other terms of the line of credit and the loan agreement and other documents evidencing the line of credit remain the same.

Note 8 - Stockholders' Equity

6 Months Ended

Feb. 28, 2018

Stockholders' Equity Note Disclosure [Text Block]

STOCKHOLDERS’ EQUITY

During the

six

months ended

February 28, 2018,

the Company’s Board of Directors declared cash dividends on the following dates in the following amounts to the following holders of the Company’s common stock:

Declaration Date	Amount	Record Date	Payable Date
November 20, 2017	$0.10	December 8, 2017	December 21, 2017
January 24, 2018	$0.10	February 8, 2018	February 21, 2018

During the

six

months ended

February 28, 2018,

the Company repurchased

shares of its common stock. During the

six

months ended

February 28, 2018,

stock options to purchase an aggregate of

1,500

shares of common stock were exercised at a weighted average exercise price of

$10.25

per share.

The Company granted stock options under the Northern Technologies International Corporation Amended and Restated

2007

Stock Incentive Plan (

2007

Plan) to purchase an aggregate of

47,252

shares of its common stock to various employees and directors during the

six

months ended

February 28, 2018.

The weighted average per share exercise price of the stock options is

$18.35,

which was equal to the fair market value of the Company’s common stock on the date of grant.

The Company issued

891

and

3,029

shares of common stock on

September 1, 2017

and

2016,

respectively, under the Northern Technologies International Corporation Employee Stock Purchase Plan (ESPP).

The Company held its

2018

Annual Meeting of Stockholders (

2018

Annual Meeting) on

January 12, 2018.

At the

2018

Annual Meeting, a proposal to approve an amendment to the Company’s Restated Certificate of Incorporation to increase the Company’s authorized shares of common stock from

10,000,000

15,000,000

(Share Increase Amendment) was approved by the Company’s stockholders by the required vote. The Share Increase Amendment was filed with the Office of the Secretary of State of the State of Delaware on

January 16, 2018

and it became effective the same day. In determining that the Share Increase Amendment was approved by the required vote, votes cast by brokers, banks or other nominees without instruction from the beneficial owners of certain of our outstanding shares were counted in favor of the proposal in accordance with the rules of the New York Stock Exchange that govern how brokers

may

cast such votes. Because a disclosure in the definitive proxy statement for the

2018

Annual Meeting, which was filed on Schedule

14A

with the Securities and Exchange Commission (SEC) on

November 27, 2017 (

2018

Proxy Statement), anticipated that brokers would

not

have discretion to vote for the proposal to approve the Share Increase Amendment, a question has been raised as to the validity of the vote taken on the proposal to approve the Share Increase Amendment. The Company believes that the Share Increase Amendment was properly approved and is effective. However, because the description of the authority of brokers to vote on proposals without instruction in the

2018

Proxy Statement

may

create some uncertainty as to the effect of the vote obtained at the

2018

Annual Meeting and out of an abundance of caution, the Company intends to ask its stockholders at either a special meeting or the next annual meeting of the Company’s stockholders to ratify the filing and effectiveness of the Share Increase Amendment pursuant to Delaware law in order to eliminate any uncertainty related to the effectiveness of the Share Increase Amendment. The Company has

not

issued, or reserved for issuance, and will

not

issue, or reserve for issuance, any of the additional

5,000,000

authorized shares as part of the Share Increase Amendment unless the vote at the special or annual meeting of the Company’s stockholders is in favor of the ratification of the Share Increase Amendment.

During the

six

months ended

February 28, 2017,

the Company repurchased and retired

11,475

shares of its common stock at a price of

$12.92

per share.

stock options to purchase shares of common stock were exercised during the

six

months ended

February 28, 2017.

The Company granted stock options under the

2007

Plan to purchase an aggregate of

56,677

shares of its common stock to various employees and directors during the

six

months ended

February 28, 2017.

The weighted average per share exercise price of the stock options was

$13.40,

which was equal to the fair market value of the Company’s common stock on the date of grant.

Note 9 - Net Income Per Common Share

6 Months Ended

Feb. 28, 2018

Earnings Per Share [Text Block]

NET INCOME PER COMMON SHARE

Basic net income per common share is computed by dividing net income by the weighted average number of common shares outstanding. Diluted net income per share assumes the exercise of stock options using the treasury stock method, if dilutive.

The following is a reconciliation of the earnings per share computation:

	Three Months Ended				Six Months Ended
Numerators:	February 28, 2018		February 28, 2017		February 28, 2018		February 28, 2017
Net income attributable to NTIC	$	1,332,847	$	386,966	$	2,416,473	$	684,605

Denominators:
Basic – weighted shares outstanding		4,537,408		4,525,091		4,537,368		4,527,555
Weighted shares assumed upon exercise of stock options		135,930		36,933		103,674		31,930
Diluted – weighted shares outstanding		4,673,338		4,562,024		4,641,042		4,559,485
Basic income per share:	$	0.29	$	0.09	$	0.53	$	0.15
Diluted income per share:	$	0.29	$	0.09	$	0.52	$	0.15

The dilutive impact summarized above relates to the periods when the average market price of the Company’s common stock exceeded the exercise price of the potentially dilutive option securities granted. Earnings per common share were based on the weighted average number of common shares outstanding during the periods when computing the basic earnings per share. When dilutive, stock options are included as equivalents using the treasury stock market method when computing the diluted earnings per share.

There were

shares excluded from the computation of diluted income per share for the

three

and

six

months ended

February 28, 2018.

Excluded from the computation of diluted earnings per share for the

three

and

six

months ended

February 28, 2017

were options outstanding to purchase

48,067

shares of common stock.

Note 10 - Stock-based Compensation

6 Months Ended

Feb. 28, 2018

Disclosure of Compensation Related Costs, Share-based Payments [Text Block]

10.

STOCK-BASED COMPENSATION

The Company has

two

stock-based compensation plans under which stock options and other stock-based awards have been granted, the Northern Technologies International Corporation Amended and Restated

2007

Stock Incentive Plan and the Northern Technologies International Corporation Employee Stock Purchase Plan (ESPP). The Compensation Committee of the Board of Directors and the Board of Directors administer these plans.

The

2007

Plan provides for the grant of incentive stock options, non-statutory stock options, stock appreciation rights, restricted stock, stock unit awards, performance awards and stock bonuses to eligible recipients to enable the Company and its subsidiaries to attract and retain qualified individuals through opportunities for equity participation in the Company, and to reward those individuals who contribute to the achievement of the Company’s economic objectives. Subject to adjustment as provided in the

2007

Plan, up to a maximum of

800,000

shares of the Company’s common stock are issuable under the

2007

Plan. Options granted under the

2007

Plan generally have a term of

ten

years and become exercisable over a

three

- or

four

-year period beginning on the

one

-year anniversary of the date of grant. Options are granted at per share exercise prices equal to the market value of the Company’s common stock on the date of grant. The Company issues new shares upon the exercise of options. As of

February 28, 2018,

only stock options and stock bonuses had been granted under the

2007

Plan.

The maximum number of shares of common stock of the Company available for issuance under the ESPP is

100,000

shares, subject to adjustment as provided in the ESPP. The ESPP provides for

six

-month offering periods beginning on

September 1

and

March 1

of each year. The purchase price of the shares is

90%

of the lower of the fair market value of common stock at the beginning or end of the offering period. This discount

may

not

exceed the maximum discount rate permitted for plans of this type under Section

423

of the Internal Revenue Code of

1986,

as amended. The ESPP is compensatory for financial reporting purposes.

The Company granted options to purchase an aggregate of

47,252

and

56,677

shares of its common stock during the

six

months ended

February 28, 2018

and

2017,

respectively. The fair value of option grants is determined at date of grant, using the Black-Scholes option pricing model with the assumptions listed below. The Company recognized compensation expense of

$206,534

and

$195,832

during the

six

months ended

February 28, 2018

and

2017,

respectively, related to the options that vested during such time period. As of

February 28, 2018,

the total compensation cost for nonvested options

not

yet recognized in the Company’s consolidated statements of operations was

$425,669.

Stock-based compensation expense of

$206,534

is expected through the remainder of fiscal year

2018,

and

$153,901

and

$65,234

is expected to be recognized during fiscal

2019

and fiscal

2020,

respectively, based on outstanding options as of

February 28, 2018.

Future option grants will impact the compensation expense recognized. Stock-based compensation expense is included in general and administrative expense on the consolidated statements of operations.

The fair value of each option grant is estimated on the grant date using the Black-Scholes option pricing model with the following assumptions and results for the grants:

	Three and Six months ended
	February 28, 2018	February 28, 2017
Dividend yield	2.18%	0.00%
Expected volatility	45.9%	46.4%
Expected life of option (in years)	10	10
Average risk-free interest rate	1.87%	1.63%

The weighted average per share fair value of options granted during the

six

months ended

February 28, 2018

and

2017

was

$7.75

and

$7.69,

respectively. The weighted average remaining contractual life of the options outstanding as of

February 28, 2018

and

2017

was

6.75

years and

6.91

years, respectively.

Note 11 - Segment and Geographical Information

6 Months Ended

Feb. 28, 2018

Segment Reporting Disclosure [Text Block]

11.

SEGMENT AND GEOGRAPHICAL INFORMATION

Segment Information

The Company’s chief operating decision maker (CODM) is its Chief Executive Officer. The Company’s business is organized into

two

reportable segments: ZERUST® and Natur-Tec®. The Company has been selling its proprietary ZERUST® rust and corrosion inhibiting products and services to the automotive, electronics, electrical, mechanical, military and retail consumer markets for over

years, and more recently, has targeted and expanded into the oil and gas industry. The Company also sells a portfolio of bio-based and compostable (fully biodegradable) polymer resins and finished products under the Natur-Tec® brand.

The following table sets forth the Company’s net sales for the

three

and

six

months ended

February 28, 2018

and

2017

by segment:

	Three Months Ended				Six Months Ended
	February 28, 2018		February 28, 2017		February 28, 2018		February 28, 2017
ZERUST® net sales	$	10,191,459	$	7,228,027	$	19,719,196	$	15,312,705
Natur-Tec® net sales		2,022,516		1,514,876		4,037,817		3,132,221
Total net sales	$	12,213,975	$	8,742,903	$	23,757,013	$	18,444,926

The following table sets forth the Company’s cost of goods sold for the

three

and

six

months ended

February 28, 2018

and

2017

by segment:

	Three Months Ended										Six Months Ended
	February 28, 2018		% of Segment Sales*			February 28, 2017		% of Segment Sales*			February 28, 2018		% of Segment Sales*			February 28, 2017		% of Segment Sales*
Direct cost of goods sold
ZERUST®	$	6,005,262		58.9	%	$	4,254,524		58.9	%	$	11,809,242		59.9	%	$	8,954,061		58.5	%
Natur-Tec®		1,447,240		71.6	%		1,068,231		70.5	%		2,926,439		72.5	%		2,281,399		72.8	%
Indirect cost of goods sold		560,334		—			547,431		—			1,165,625		—			1,247,492		—
Total net cost of goods sold	$	8,012,836				$	5,870,186				$	15,901,306				$	12,482,952

___________________________________

The percent of segment sales is calculated by dividing the direct cost of goods sold for each individual segment category by the net sales for each segment category.

The Company utilizes product net sales and direct and indirect cost of goods sold for each product in reviewing the financial performance of a product type. Further allocation of Company expenses or assets, aside from amounts presented in the tables above, is

not

utilized in evaluating product performance, nor does such allocation occur for internal financial reporting.

Geographic Information

Net sales by geographic location for the

three

and

six

months ended

February 28, 2018

and

2017

were as follows:

	Three Months Ended				Six Months Ended
	February 28, 2018		February 28, 2017		February 28, 2018		February 28, 2017
Inside the U.S.A. to unaffiliated customers	$	6,079,835	$	5,245,092	$	12,336,040	$	10,395,832
Outside the U.S.A to:
Joint ventures in which the Company is shareholder directly and indirectly		814,122		433,317		1,321,753		1,253,375
Unaffiliated customers		5,320,018		3,064,494		10,099,220		6,795,719
	$	12,213,975	$	8,742,903	$	23,757,013	$	18,444,926

Net sales by geographic location are based on the location of the customer.

Fees for services provided to joint ventures by geographic location as a percentage of total fees for services provided to joint ventures during the

three

and

six

months ended

February 28, 2018

and

2017

were as follows:

	Three Months Ended
	February 28, 2018		% of Total Fees for Services Provided to Joint Ventures			February 28, 2017		% of Total Fees for Services Provided to Joint Ventures
Germany	$	236,700		14.7	%	$	199,509		16.8	%
Poland		207,038		12.9	%		153,453		13.0	%
Japan		172,032		10.7	%		145,722		12.3	%
Sweden		165,165		10.3	%		77,464		6.5	%
India		138,437		8.6	%		74,196		6.3	%
France		130,323		8.1	%		83,112		7.0	%
Thailand		111,779		6.9	%		87,627		7.4	%
Korea		99,574		6.2	%		86,103		7.3	%
Czech Republic		98,726		6.1	%		73,286		6.2	%
United Kingdom		82,432		5.1	%		53,241		4.5	%
Finland		76,546		4.8	%		66,946		5.7	%
Other		90,138		5.6	%		83,369		7.0	%
	$	1,608,890		100.0	%	$	1,184,028		100.0	%

	Six Months Ended
	February 28, 2018		% of Total Fees for Services Provided to Joint Ventures			February 28, 2017		% of Total Fees for Services Provided to Joint Ventures
Germany	$	456,574		14.7	%	$	402,509		16.1	%
Poland		413,114		13.3	%		302,657		12.1	%
Japan		346,077		11.1	%		291,759		11.7	%
Sweden		293,119		9.4	%		164,525		6.6	%
France		269,964		8.7	%		180,785		7.2	%
India		225,200		7.2	%		138,731		5.6	%
Thailand		214,311		6.9	%		235,081		9.4	%
United Kingdom		194,207		6.2	%		139,372		5.6	%
Korea		183,062		5.9	%		191,481		7.6	%
Czech Republic		182,951		5.8	%		144,114		5.8	%
Finland		166,172		5.3	%		143,282		5.7	%
Other		171,281		5.5	%		165,323		6.6	%
	$	3,116,032		100.0	%	$	2,499,619		100.0	%

The geographical distribution of key financial statement data is as follows:

	At February 28, 2018		At August 31, 2017
China	$	222,089	$	228,458
Brazil		49,748		54,646
Germany		13,813		14,171
India		13,186		14,712
United States		6,857,110		7,047,675
Total property and equipment	$	7,155,946	$	7,359,662

	Six Months Ended
	February 28, 2018		February 28, 2017
China	$	6,106,942	$	3,296,299
Brazil		1,456,456		1,118,166
India		1,078,294		733,581
Germany		244,802		217,496
Other		1,363,151		1,531,759
United States		13,507,368		11,547,625
Total net sales	$	23,757,013	$	18,444,926

Total property and equipment are periodically reviewed to assure the net realizable value from the estimated future production based on forecasted sales exceeds the carrying value of the assets.

Sales to the Company’s joint ventures are included in the foregoing segment and geographic information; however, sales by the Company’s joint ventures to other parties are

not

included. The foregoing segment and geographic information represents only sales and cost of goods sold recognized directly by the Company.

All joint venture operations, including equity in income, fees for services and related dividends, are primarily related to ZERUST

products and services.

Note 12 - Commitments and Contingencies	6 Months Ended
Note 12 - Commitments and Contingencies	Feb. 28, 2018
Notes to Financial Statements
Commitments and Contingencies Disclosure [Text Block]	12. COMMITMENTS AND CONTINGENCIES On August 31, 2017, the Compensation Committee of the Board of Directors of the Company approved the material terms of an annual bonus plan for the Company’s executive officers as well as certain officers and employees for the fiscal year ending August 31, 2018. For fiscal 2018 as in past years, the total amount available under the bonus plan for all plan participants, including executive officers, is dependent upon the Company’s earnings before interest, taxes and other income, as adjusted to take into account amounts to be paid under the bonus plan and certain other adjustments (Adjusted EBITOI). Each plan participant’s percentage of the overall bonus pool is based upon the number of plan participants, the individual’s annual base salary and the individual’s position and level of responsibility within the Company. In the case of each of the Company’s executive officer participants, 75% of the amount of their individual bonus payout will be determined based upon the Company’s actual EBITOI for fiscal 2018 compared to a pre-established target EBITOI for fiscal 2018 and 25% of the payout will be determined based upon such executive officer’s achievement of certain pre-established individual performance objectives. The payment of bonuses under the plan are discretionary and may be paid to executive officer participants in both cash and shares of the Company’s common stock, the exact amount and percentages will be determined by the Company’s Board of Directors, upon recommendation of the Compensation Committee, after the completion of the Company’s consolidated financial statements for fiscal 2018. There was $880,000 accrued for management bonuses for the six months ended February 28, 2018 compared to $185,000 accrued for management bonuses for the six months ended February 28, 2017. Three joint ventures (consisting of the Company’s joint ventures in South Korea, India and United States) accounted for 69.8% of the Company’s trade joint venture receivables at February 28, 2018 and three joint ventures (consisting of the Company’s joint ventures in South Korea, Thailand and India) accounted for 60.7% of the Company’s trade joint venture receivables at August 31, 2017. From time to time, the Company is subject to various other claims and legal actions in the ordinary course of its business. The Company records a liability in its consolidated financial statements for costs related to claims, including future legal costs, settlements and judgments, where the Company has assessed that a loss is probable and an amount could be reasonably estimated. If the reasonable estimate of a probable loss is a range, the Company records the most probable estimate of the loss or the minimum amount when no amount within the range is a better estimate than any other amount. The Company discloses a contingent liability even if the liability is not probable or the amount is not estimable, or both, if there is a reasonable possibility that material loss may have been incurred. In the opinion of management, as of February 28, 2018, the amount of liability, if any, with respect to these matters, individually or in the aggregate, will not materially affect the Company’s consolidated results of operations, financial position or cash flows.

Note 13 - Fair Value Measurements

6 Months Ended

Feb. 28, 2018

Fair Value, Measurement Inputs, Disclosure [Text Block]

13.

FAIR VALUE MEASUREMENTS

Assets and liabilities that are measured at fair value on a recurring basis primarily relate to marketable equity securities. These items are marked-to-market at each reporting period. The following tables provide information by level for assets and liabilities that are measured at fair value on a recurring basis:

			Fair Value Measurements Using Inputs Considered as
	Fair value as of February 28, 2018		Level 1		Level 2		Level 3
Available for sale securities	$	3,268,426	$	3,268,426	$	—	$	—

			Fair Value Measurements Using Inputs Considered as
	Fair value as of August 31, 2017		Level 1		Level 2		Level 3
Available for sale securities	$	3,766,984	$	3,766,984	$	—	$	—

There were

transfers between Level

Level

or Level

during the

three

and

six

months ended

February 28, 2018

and

2017.

Note 15 - Income Taxes	6 Months Ended
Note 15 - Income Taxes	Feb. 28, 2018
Notes to Financial Statements
Income Tax Disclosure [Text Block]	15. INCOME TAXES On December 22, 2017, the U.S. government enacted comprehensive tax legislation commonly referred to as the Tax Cuts and Jobs Act, or Tax Reform Act. The Tax Reform Act makes broad and complex changes to the U.S. tax code that will affect the Company’s fiscal year ending August 31 2018, including, but not limited to, reducing the U.S. federal corporate tax rate from 35% to 21% effective January 1, 2018, generally eliminating U.S. federal income taxes on dividends received from foreign subsidiaries and joint ventures after December 31, 2017, and imposing a one -time deemed repatriation tax on certain unremitted earnings of foreign subsidiaries and joint ventures. The Company will be subject to a blended U.S. federal tax rate of 25.7% for the fiscal year ending August 31, 2018 as a result of the reduction of the U.S. federal corporate tax rate from 35% to 21% effective January 1, 2018. The Company recognized the income tax effects of the Tax Reform Act in its 2018 interim consolidated financial statements in accordance with SAB No. 118, which provides SEC staff guidance for the application of ASC Topic 740, Income Taxes , in the reporting period in which the Tax Reform Act was signed into law. As such, the Company’s financial results reflect the income tax effects of the Tax Reform Act for which the accounting under ASC Topic 740 is complete and provisional amounts for those specific income tax effects of the Tax Reform Act for which the accounting under ASC Topic 740 is incomplete but a reasonable estimate could be determined. The Company recorded income tax expense during the three and six months ended February 28, 2018 of $841,909 and $946,900, respectively, compared to $124,909 and $242,622 for the three and six months ended February 28, 2017. The Company’s effective tax rate for the three and six months ended February 28, 2018 was 37.2% and 26.5%, respectively, compared to 20.5% and 21.3% for the three and six months ended February 28, 2017, respectively. The Company measures deferred tax assets and liabilities using enacted tax rates that will apply in the years in which the temporary differences are expected to be recovered or paid. Accordingly, the Company’s deferred tax assets and liabilities were re-measured to reflect the reduction in the U.S. corporate income tax rate from 35% to 21% effective January 1, 2018, resulting in an increase of $700,000 in income tax expense for the three months ended February 28, 2018 and a corresponding decrease of $700,000 in net deferred tax assets as of February 28, 2018. The $700,000 income tax expense and corresponding decrease in net deferred tax assets represents a provisional estimate based on the Company’s current interpretation of the Tax Reform Act and may change as the Company receives additional clarification and implementation guidance. The one -time deemed repatriation tax is applicable to the unremitted earnings of the Company’s foreign subsidiaries and joint ventures. The Company calculated deemed repatriation tax of $489,000, which the Company expects to fully offset with foreign tax credit carryforwards for which the Company has not previously recognized a tax benefit. As a result, the transition tax resulted in zero increase in income tax expense and income taxes payable for the three months ended February 28, 2018. The $489,000 transition tax on deemed repatriation of unremitted foreign earnings represents a provisional estimate and is subject to adjustment during the measurement period of up to one year following the December 2017 enactment date of the Tax Reform Act, as provided by recent SEC guidance. The Company continues to analyze the impact of other provisions of the Tax Reform Act on its financial statements and operations, including the impact of the global intangible low-taxed income (GILTI) rules, and the impact of the Tax Reform Act on the Company’s indefinite reinvestment assertion with respect to the undistributed earnings of certain foreign subsidiaries and joint ventures. Any additional impacts from the enactment of the Tax Reform Act will be recorded as they are identified during the measurement period as provided for in accordance with SAB No. 118.

Note 3 - Inventories (Tables)

6 Months Ended

Feb. 28, 2018

Schedule of Inventory, Current [Table Text Block]

	February 28, 2018		August 31, 2017
Production materials	$	1,820,942	$	1,747,189
Finished goods		7,305,229		5,709,363
	$	9,126,171	$	7,456,552

Note 6 - Investments in Joint Ventures (Tables)

6 Months Ended

Feb. 28, 2018

Condensed Balance Sheet [Table Text Block]

	As of February 28, 2018
	Total		EXCOR		All Other
Current assets	$	57,427,392	$	25,206,550	$	32,220,842
Total assets		61,497,315		27,326,727		34,170,588
Current liabilities		16,468,617		4,148,371		12,320,246
Noncurrent liabilities		120,481		—		120,481
Joint ventures’ equity		44,908,217		23,178,356		21,729,861
Northern Technologies International Corporation’s share of joint ventures’ equity		22,259,526		11,589,180		10,670,346
Northern Technologies International Corporation’s share of joint ventures’ undistributed earnings	$	20,230,286	$	11,558,275	$	8,672,011
Northern Technologies International Corporation’s dividends received from joint ventures	$	1,770,116	$	1,199,142	$	570,974

	As of August 31, 2017
	Total		EXCOR		All Other
Current assets	$	51,518,210	$	22,142,514	$	29,375,696
Total assets		55,633,891		24,301,194		31,332,697
Current liabilities		15,118,074		4,469,567		10,648,507
Noncurrent liabilities		181,210		—		181,210
Joint ventures’ equity		40,334,607		19,831,627		20,502,980
Northern Technologies International Corporation’s share of joint ventures’ equity		20,035,074		9,915,816		10,119,258
Northern Technologies International Corporation’s share of joint ventures’ undistributed earnings		17,960,860		9,884,911		8,075,949
Northern Technologies International Corporation’s dividends received from joint ventures	$	6,377,054	$	5,379,062	$	997,992

Condensed Income Statement [Table Text Block]

	Three Months Ended February 28, 2018
	Total		EXCOR		All Other
Net sales	$	30,220,550	$	12,204,736	$	18,015,814
Gross profit		13,531,276		6,557,964		6,973,312
Net income		3,712,684		2,674,777		1,037,907
Northern Technologies International Corporation’s share of equity in income from joint ventures	$	1,805,997	$	1,338,671	$	467,326

	Six Months Ended February 28, 2018
	Total		EXCOR		All Other
Net sales	$	58,719,261	$	23,231,250	$	35,488,011
Gross profit		26,319,398		12,491,490		13,827,908
Net income		7,212,499		5,158,577		2,053,922
Northern Technologies International Corporation’s share of equity in income from joint ventures	$	3,547,325	$	2,580,571	$	966,754

	Three Months Ended February 28, 2017
	Total		EXCOR		All Other
Net sales	$	22,962,599	$	9,076,908	$	13,885,691
Gross profit		10,161,509		4,867,517		5,293,992
Net income		2,774,943		2,161,408		613,535
Northern Technologies International Corporation’s share of equity in income from joint ventures	$	1,383,139	$	1,078,272	$	304,867

	Six Months Ended February 28, 2017
	Total		EXCOR		All Other
Net sales	$	47,163,046	$	18,285,432	$	28,877,614
Gross profit		20,858,536		9,761,696		11,096,840
Net income		5,182,951		4,017,746		1,165,205
Northern Technologies International Corporation’s share of equity in income from joint ventures	$	2,657,143	$	2,006,441	$	650,702

Note 11 - Segment and Geographical Information (Tables)

6 Months Ended

Feb. 28, 2018

Reconciliation of Revenue from Segments to Consolidated [Table Text Block]

	Three Months Ended				Six Months Ended
	February 28, 2018		February 28, 2017		February 28, 2018		February 28, 2017
ZERUST® net sales	$	10,191,459	$	7,228,027	$	19,719,196	$	15,312,705
Natur-Tec® net sales		2,022,516		1,514,876		4,037,817		3,132,221
Total net sales	$	12,213,975	$	8,742,903	$	23,757,013	$	18,444,926

Reconciliation of Cost of Goods Sold from Segments to Consolidated [Table Text Block]

	Three Months Ended										Six Months Ended
	February 28, 2018		% of Segment Sales*			February 28, 2017		% of Segment Sales*			February 28, 2018		% of Segment Sales*			February 28, 2017		% of Segment Sales*
Direct cost of goods sold
ZERUST®	$	6,005,262		58.9	%	$	4,254,524		58.9	%	$	11,809,242		59.9	%	$	8,954,061		58.5	%
Natur-Tec®		1,447,240		71.6	%		1,068,231		70.5	%		2,926,439		72.5	%		2,281,399		72.8	%
Indirect cost of goods sold		560,334		—			547,431		—			1,165,625		—			1,247,492		—
Total net cost of goods sold	$	8,012,836				$	5,870,186				$	15,901,306				$	12,482,952

Schedule of Revenue from External Customers Attributed to Foreign Countries by Geographic Area [Table Text Block]

	Three Months Ended				Six Months Ended
	February 28, 2018		February 28, 2017		February 28, 2018		February 28, 2017
Inside the U.S.A. to unaffiliated customers	$	6,079,835	$	5,245,092	$	12,336,040	$	10,395,832
Outside the U.S.A to:
Joint ventures in which the Company is shareholder directly and indirectly		814,122		433,317		1,321,753		1,253,375
Unaffiliated customers		5,320,018		3,064,494		10,099,220		6,795,719
	$	12,213,975	$	8,742,903	$	23,757,013	$	18,444,926

Schedule of Revenue from External Customers and Long-Lived Assets, by Geographical Areas [Table Text Block]

	At February 28, 2018		At August 31, 2017
China	$	222,089	$	228,458
Brazil		49,748		54,646
Germany		13,813		14,171
India		13,186		14,712
United States		6,857,110		7,047,675
Total property and equipment	$	7,155,946	$	7,359,662

Revenue from External Customers by Geographic Areas [Table Text Block]

	Six Months Ended
	February 28, 2018		February 28, 2017
China	$	6,106,942	$	3,296,299
Brazil		1,456,456		1,118,166
India		1,078,294		733,581
Germany		244,802		217,496
Other		1,363,151		1,531,759
United States		13,507,368		11,547,625
Total net sales	$	23,757,013	$	18,444,926

Fees for Services Provided to Joint Ventures [Member]

Reconciliation of Revenue from Segments to Consolidated [Table Text Block]

	Three Months Ended
	February 28, 2018		% of Total Fees for Services Provided to Joint Ventures			February 28, 2017		% of Total Fees for Services Provided to Joint Ventures
Germany	$	236,700		14.7	%	$	199,509		16.8	%
Poland		207,038		12.9	%		153,453		13.0	%
Japan		172,032		10.7	%		145,722		12.3	%
Sweden		165,165		10.3	%		77,464		6.5	%
India		138,437		8.6	%		74,196		6.3	%
France		130,323		8.1	%		83,112		7.0	%
Thailand		111,779		6.9	%		87,627		7.4	%
Korea		99,574		6.2	%		86,103		7.3	%
Czech Republic		98,726		6.1	%		73,286		6.2	%
United Kingdom		82,432		5.1	%		53,241		4.5	%
Finland		76,546		4.8	%		66,946		5.7	%
Other		90,138		5.6	%		83,369		7.0	%
	$	1,608,890		100.0	%	$	1,184,028		100.0	%

	Six Months Ended
	February 28, 2018		% of Total Fees for Services Provided to Joint Ventures			February 28, 2017		% of Total Fees for Services Provided to Joint Ventures
Germany	$	456,574		14.7	%	$	402,509		16.1	%
Poland		413,114		13.3	%		302,657		12.1	%
Japan		346,077		11.1	%		291,759		11.7	%
Sweden		293,119		9.4	%		164,525		6.6	%
France		269,964		8.7	%		180,785		7.2	%
India		225,200		7.2	%		138,731		5.6	%
Thailand		214,311		6.9	%		235,081		9.4	%
United Kingdom		194,207		6.2	%		139,372		5.6	%
Korea		183,062		5.9	%		191,481		7.6	%
Czech Republic		182,951		5.8	%		144,114		5.8	%
Finland		166,172		5.3	%		143,282		5.7	%
Other		171,281		5.5	%		165,323		6.6	%
	$	3,116,032		100.0	%	$	2,499,619		100.0	%

Note 13 - Fair Value Measurements (Tables)

6 Months Ended

Feb. 28, 2018

Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Table Text Block]

			Fair Value Measurements Using Inputs Considered as
	Fair value as of February 28, 2018		Level 1		Level 2		Level 3
Available for sale securities	$	3,268,426	$	3,268,426	$	—	$	—

			Fair Value Measurements Using Inputs Considered as
	Fair value as of August 31, 2017		Level 1		Level 2		Level 3
Available for sale securities	$	3,766,984	$	3,766,984	$	—	$	—

Note 3 - Inventories - Inventories (Details) - USD ($)	Feb. 28, 2018	Aug. 31, 2017
Production materials	$ 1,820,942	$ 1,747,189
Finished goods	7,305,229	5,709,363
Total inventory	$ 9,126,171	$ 7,456,552

Note 4 - Property and Equipment, Net - Components of Property and Equipment, Net (Details) - USD ($)	Feb. 28, 2018	Aug. 31, 2017
Land	$ 310,365	$ 310,365
Buildings and improvements	6,815,771	6,847,177
Machinery and equipment	4,414,136	4,171,387
Gross	11,540,272	11,328,929
Less accumulated depreciation	(4,384,326)	(3,969,267)
Net	$ 7,155,946	$ 7,359,662

Note 5 - Patents and Trademarks, Net (Details Textual) - Patents and Trademarks [Member]	6 Months Ended
	Feb. 28, 2018 USD ($)
Finite-Lived Intangible Asset, Useful Life	7 years
Finite-Lived Intangible Assets, Amortization Expense, Next Twelve Months	$ 240,000
Finite-Lived Intangible Assets, Amortization Expense, Year Five	240,000
Finite-Lived Intangible Assets, Amortization Expense, Year Two	240,000
Finite-Lived Intangible Assets, Amortization Expense, Year Three	240,000
Finite-Lived Intangible Assets, Amortization Expense, Year Four	$ 240,000

Note 5 - Patents and Trademarks, Net - Patents and Trademarks, Net (Details) - USD ($)	Feb. 28, 2018	Aug. 31, 2017
Patents and trademarkes, net	$ 1,241,618	$ 1,322,089
Patents and Trademarks [Member]
Patents and trademarks	2,782,580	2,737,959
Less accumulated amortization	(1,540,962)	(1,415,870)
Patents and trademarkes, net	$ 1,241,618	$ 1,322,089

Note 6 - Investments in Joint Ventures - Condensed Balance Sheet of EXCOR and All Other Joint Ventures (Details) - USD ($)	6 Months Ended	12 Months Ended
	Feb. 28, 2018	Aug. 31, 2017
Current assets	$ 57,427,392	$ 51,518,210
Total assets	61,497,315	55,633,891
Current liabilities	16,468,617	15,118,074
Noncurrent liabilities	120,481	181,210
Joint ventures’ equity	44,908,217	40,334,607
Northern Technologies International Corporation’s share of joint ventures’ equity	22,259,526	20,035,074
Northern Technologies International Corporation’s share of joint ventures’ undistributed earnings	20,230,286	17,960,860
Northern Technologies International Corporation’s dividends received from joint ventures	1,770,116	6,377,054
EXCOR [Member]
Current assets	25,206,550	22,142,514
Total assets	27,326,727	24,301,194
Current liabilities	4,148,371	4,469,567
Noncurrent liabilities
Joint ventures’ equity	23,178,356	19,831,627
Northern Technologies International Corporation’s share of joint ventures’ equity	11,589,180	9,915,816
Northern Technologies International Corporation’s share of joint ventures’ undistributed earnings	11,558,275	9,884,911
Northern Technologies International Corporation’s dividends received from joint ventures	1,199,142	5,379,062
All Other [Member]
Current assets	32,220,842	29,375,696
Total assets	34,170,588	31,332,697
Current liabilities	12,320,246	10,648,507
Noncurrent liabilities	120,481	181,210
Joint ventures’ equity	21,729,861	20,502,980
Northern Technologies International Corporation’s share of joint ventures’ equity	10,670,346	10,119,258
Northern Technologies International Corporation’s share of joint ventures’ undistributed earnings	8,672,011	8,075,949
Northern Technologies International Corporation’s dividends received from joint ventures	$ 570,974	$ 997,992

Note 6 - Investments in Joint Ventures - Condensed Income Statement of EXCOR and All Other Joint Ventures (Details) - USD ($)	3 Months Ended		6 Months Ended
	Feb. 28, 2018	Feb. 28, 2017	Feb. 28, 2018	Feb. 28, 2017
Net sales	$ 30,220,550	$ 22,962,599	$ 58,719,261	$ 47,163,046
Gross profit	13,531,276	10,161,509	26,319,398	20,858,536
Net income	3,712,684	2,774,943	7,212,499	5,182,951
Northern Technologies International Corporation’s share of equity in income from joint ventures	1,805,997	1,383,139	3,547,325	2,657,143
EXCOR [Member]
Net sales	12,204,736	9,076,908	23,231,250	18,285,432
Gross profit	6,557,964	4,867,517	12,491,490	9,761,696
Net income	2,674,777	2,161,408	5,158,577	4,017,746
Northern Technologies International Corporation’s share of equity in income from joint ventures	1,338,671	1,078,272	2,580,571	2,006,441
All Other [Member]
Net sales	18,015,814	13,885,691	35,488,011	28,877,614
Gross profit	6,973,312	5,293,992	13,827,908	11,096,840
Net income	1,037,907	613,535	2,053,922	1,165,205
Northern Technologies International Corporation’s share of equity in income from joint ventures	$ 467,326	$ 304,867	$ 966,754	$ 650,702

Note 7 - Corporate Debt (Details Textual)	6 Months Ended
Note 7 - Corporate Debt (Details Textual)	Feb. 28, 2018 USD ($)	Aug. 31, 2017 USD ($)
Term Loan and Line of Credit, Agreements, Loan Agreements [Member]
Debt Instrument, Covenants, Fixed Charge Coverage Ratio	1.1
PNC Bank [Member]
Letters of Credit Outstanding, Amount	$ 0	$ 0
PNC Bank [Member] \| Revolving Credit Facility [Member]
Line of Credit Facility, Maximum Borrowing Capacity	3,000,000
Long-term Line of Credit	$ 0	0
PNC Bank [Member] \| Revolving Credit Facility [Member] \| London Interbank Offered Rate (LIBOR) [Member]
Debt Instrument, Basis Spread on Variable Rate	2.15%
PNC Bank [Member] \| Letter of Credit [Member]
Line of Credit Facility, Maximum Borrowing Capacity	$ 1,200,000
JP Morgan Chase Bank [Member]
Letters of Credit Outstanding, Amount	$ 88,831	$ 89,543

Note 8 - Stockholders' Equity (Details Textual) - $ / shares			2 Months Ended	6 Months Ended
	Sep. 01, 2017	Sep. 01, 2016	Feb. 28, 2018	Feb. 28, 2018	Feb. 28, 2017	Jan. 15, 2018	Aug. 31, 2017
Stock Repurchased and Retired During Period, Shares				0	11,475
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercises in Period				1,500	0
Share-based Compensation Arrangements by Share-based Payment Award, Options, Exercises in Period, Weighted Average Exercise Price				$ 10.25
Stock Issued During Period, Shares, Employee Stock Purchase Plans	891	3,029
Common Stock, Shares Authorized			15,000,000	15,000,000		10,000,000	10,000,000
Common Stock, Additional Shares Authorized			5,000,000
Treasury Stock Acquired, Average Cost Per Share					$ 12.92
The 2007 Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Gross				47,252	56,677
Share-based Compensation Arrangements by Share-based Payment Award, Options, Grants in Period, Weighted Average Exercise Price				$ 18.35	$ 13.40

Note 8 - Stockholders' Equity - Schedule of Dividends Payable (Details) - $ / shares			3 Months Ended		6 Months Ended
	Jan. 24, 2018	Nov. 20, 2017	Feb. 28, 2018	Feb. 28, 2017	Feb. 28, 2018	Feb. 28, 2017
Declaration Date	Jan. 24, 2018	Nov. 20, 2017
Amount (in dollars per share)	$ 0.10	$ 0.10	$ 0.10	$ 0	$ 0.20	$ 0
Record Date	Feb. 08, 2018	Dec. 08, 2017
Payable Date	Feb. 21, 2018	Dec. 21, 2017

Note 9 - Net Income Per Common Share - Reconciliation of the Earnings Per Share Computations (Details) - USD ($)	3 Months Ended		6 Months Ended
	Feb. 28, 2018	Feb. 28, 2017	Feb. 28, 2018	Feb. 28, 2017
Net income attributable to NTIC	$ 1,332,847	$ 386,966	$ 2,416,473	$ 684,605
Basic – weighted shares outstanding (in shares)	4,537,408	4,525,091	4,537,368	4,527,555
Weighted shares assumed upon exercise of stock options (in shares)	135,930	36,933	103,674	31,930
Diluted – weighted shares outstanding (in shares)	4,673,338	4,562,024	4,641,042	4,559,485
Basic income per share: (in dollars per share)	$ 0.29	$ 0.09	$ 0.53	$ 0.15
Diluted income per share: (in dollars per share)	$ 0.29	$ 0.09	$ 0.52	$ 0.15

Note 10 - Stock-based Compensation (Details Textual)	6 Months Ended
Note 10 - Stock-based Compensation (Details Textual)	Feb. 28, 2018 USD ($) $ / shares shares	Feb. 28, 2017 USD ($) $ / shares shares
Number of Stock-based Compensation Plans	2
Stock or Unit Option Plan Expense	$ 206,534	$ 195,832
Employee Service Share-based Compensation, Nonvested Awards, Compensation Not yet Recognized, Stock Options	425,669
Allocated Share-based Compensation Expense, Estimate Remainder of Fiscal Year	206,534
Allocated Share-based Compensation Expense, Estimate, Next Fiscal Year	153,901
Allocated Share-based Compensation Expense, Estimate, Fiscal Year Two	$ 65,234
Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Weighted Average Grant Date Fair Value \| $ / shares	$ 7.75	$ 7.69
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Remaining Contractual Term	6 years 273 days	6 years 332 days
The 2007 Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Authorized \| shares	800,000
Share-based Compensation Arrangement by Share-based Payment Award, Expiration Period	10 years
Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Gross \| shares	47,252	56,677
The 2007 Plan [Member] \| One Year after Date of Grant [Member] \| Minimum [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Period	3 years
The 2007 Plan [Member] \| One Year after Date of Grant [Member] \| Maximum [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Period	4 years
ESPP [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Authorized \| shares	100,000
Share-based Compensation Arrangement by Share-based Payment Award, Purchase Price of Common Stock, Percent	90.00%

Note 10 - Stock-based Compensation - Black-scholes Option-pricing Model Assumptions (Details)	6 Months Ended
	Feb. 28, 2018	Feb. 28, 2017
Dividend yield	2.18%	0.00%
Expected volatility	45.90%	46.40%
Expected life of option (Year)	10 years	10 years
Average risk-free interest rate	1.87%	1.63%

Note 11 - Segment and Geographical Information - Cost of Goods Sold by Segment (Details) - USD ($)

3 Months Ended

6 Months Ended

Feb. 28, 2018

Feb. 28, 2017

Feb. 28, 2018

Feb. 28, 2017

$ 8,012,836

$ 5,870,186

$ 15,901,306

$ 12,482,952

Direct Cost of Goods Sold [Member] | ZERUST [Member]

^[1]

$ 6,005,262

$ 4,254,524

$ 11,809,242

$ 8,954,061

Direct Cost of Goods Sold [Member] | NaturTec [Member]

^[1]

58.90%

59.90%

58.50%

$ 1,447,240

$ 1,068,231

$ 2,926,439

$ 2,281,399

Indirect Cost of Goods Sold [Member]

^[1]

71.60%

70.50%

72.50%

72.80%

$ 560,334

$ 547,431

$ 1,165,625

$ 1,247,492