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Credit Arrangements (Narrative) (Details) - USD ($)
12 Months Ended
Aug. 31, 2021
Sep. 01, 2021
Aug. 31, 2020
Debt Instrument [Line Items]      
Long-term Debt $ 116,148,000   $ 116,344,000
Elecsys Series 2006A Bonds [Member]      
Debt Instrument [Line Items]      
Long-term Debt $ 1,148,000   1,344,000
Maturity date Sep. 01, 2026    
Variable interest rate 0.45%    
Effective interest rate 1.92%    
Interest rate adjustment period 5 years    
Elecsys Series 2006A Bonds [Member] | Subsequent Event [Member]      
Debt Instrument [Line Items]      
Effective interest rate   1.72%  
Elecsys Series 2006A Bond Adjusted Rate [Member]      
Debt Instrument [Line Items]      
Maturity date Sep. 01, 2021    
Revolving Credit Facility [Member]      
Debt Instrument [Line Items]      
Long-term Debt $ 0   0
Maturity date Aug. 26, 2026    
Unsecured revolving line of credit, maximum borrowing capacity outstanding $ 50,000,000.0    
Unsecured revolving line of credit, amount outstanding 0   0
Line of Credit Facility, Remaining Borrowing Capacity $ 50,000,000.0    
Annual commitment fee 0.125%    
Revolving Credit Facility [Member] | Minimum [Member]      
Debt Instrument [Line Items]      
Annual commitment fee 0.125%    
Revolving Credit Facility [Member] | Maximum [Member]      
Debt Instrument [Line Items]      
Line of credit facility, additional borrowing capacity $ 50,000,000.0    
Annual commitment fee 0.20%    
Revolving Credit Facility [Member] | SOFR [Member]      
Debt Instrument [Line Items]      
Variable interest rate 1.40%    
Revolving Credit Facility [Member] | SOFR [Member] | Minimum [Member]      
Debt Instrument [Line Items]      
Variable interest rate 1.00%    
Revolving Credit Facility [Member] | SOFR [Member] | Maximum [Member]      
Debt Instrument [Line Items]      
Variable interest rate 2.10%    
Series A Senior Notes [Member]      
Debt Instrument [Line Items]      
Long-term Debt $ 115,000,000   $ 115,000,000
Face amount $ 115,000,000.0    
Maturity date Feb. 19, 2030    
Interest rate 3.82%