Note 14 - Stock-based Compensation - Summary of Stock Option Weighted Average Assumptions of Non-employee Director Stock Options (Details)		3 Months Ended	9 Months Ended
		May 31, 2018	May 31, 2019	May 31, 2018
Risk-free interest rate	[1]
Expected volatility	[1]
Non Employee Directors Stock Option Plan [Member] | Share-based Payment Arrangement, Option [Member]
Risk-free interest rate			2.51%	2.34%
Expected life (Year)			5 years 146 days	5 years 146 days
Expected volatility			20.50%	19.70%
Dividend yield			1.17%	1.16%

[1] There were no employee stock options granted during the three months ended May 31, 2018.