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Note 1 - Summary of Significant Accounting Policies (Details Textual)
12 Months Ended
Mar. 31, 2020
USD ($)
Mar. 31, 2019
USD ($)
Mar. 31, 2018
USD ($)
Accounts Receivable, Allowance for Credit Loss, Current $ 59,000 $ 39,000  
Inventory Valuation Reserves, Ending Balance 45,000 54,000  
OCI, Debt Securities, Available-for-Sale, Unrealized Holding Gain (Loss), before Adjustment, after Tax 0 $ 0 $ 0
Accounting Standards Update 2016-02 [Member] | Accrued Expenses and Other Current Liabilities [Member]      
Operating Lease, Right-of-Use Asset 110,000    
Operating Lease, Liability, Current $ 110,000    
Cost of Goods and Service Benchmark [Member] | Supplier Concentration Risk [Member]      
Number of Suppliers 3 4  
Concentration Risk, Percentage 60.00% 50.00%  
Building [Member]      
Property, Plant and Equipment, Useful Life (Year) 30 years    
Furniture, Fixtures, Equipment and Computer Software [Member] | Minimum [Member]      
Property, Plant and Equipment, Useful Life (Year) 3 years    
Furniture, Fixtures, Equipment and Computer Software [Member] | Maximum [Member]      
Property, Plant and Equipment, Useful Life (Year) 10 years