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Note 7 - Long-term Debt (Details Textual)
9 Months Ended
Apr. 01, 2021
USD ($)
Apr. 29, 2016
USD ($)
ft²
Sep. 30, 2021
USD ($)
Dec. 31, 2020
USD ($)
Apr. 01, 2016
USD ($)
Line of Credit [Member]          
Line of Credit Facility, Maximum Borrowing Capacity     $ 2,050,000    
Long-term Line of Credit, Total     $ 0 $ 0  
Line of Credit [Member] | London Interbank Offered Rate (LIBOR) [Member]          
Debt Instrument, Basis Spread on Variable Rate     0.85%    
Loan [Member]          
Debt Instrument, Periodic Payment, Total   $ 18,000      
Debt Instrument, Interest Rate, Stated Percentage   2.60%      
Debt Issuance Costs, Gross   $ 139,000      
Debt Instrument, Interest Rate, Effective Percentage   3.23%      
Repayments of Debt $ 2,700,000        
Interest Paid, Including Capitalized Interest, Operating and Investing Activities, Total 6,100        
Write off of Deferred Debt Issuance Cost $ 82,000        
Loan [Member] | Building [Member]          
Area of Real Estate Property (Square Foot) | ft²   27,300      
Duluth Economic Development Authority [Member]          
Tax Exempt Industrial Revenue Bonds Amount Sold to Bank         $ 3,415,000