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Note 2 - Significant Accounting Policies (Details Textual)
12 Months Ended
Mar. 31, 2020
USD ($)
Mar. 31, 2019
USD ($)
Mar. 31, 2018
USD ($)
Cash, Uninsured Amount $ 1,917,000 $ 340,000  
Asset Retirement Obligation, Ending Balance 0 0  
Contract with Customer, Liability, Revenue Recognized 550,000 133,000  
Advertising Expense 1,992,000 2,413,000 $ 1,548,000
Unrecognized Tax Benefits, Ending Balance 0 0  
Unrecognized Tax Benefits, Income Tax Penalties and Interest Accrued, Total $ 0 $ 0  
Customer Concentration Risk [Member] | Revenue Benchmark [Member]      
Number of Major Customers 2 2 2
Customer Concentration Risk [Member] | Revenue Benchmark [Member] | Customer Number 1 [Member]      
Concentration Risk, Percentage 33.00% 33.00% 32.00%
Customer Concentration Risk [Member] | Revenue Benchmark [Member] | Customer Number 2 [Member]      
Concentration Risk, Percentage 18.00% 24.00% 15.00%
Customer Concentration Risk [Member] | Accounts Receivable [Member]      
Number of Major Customers 2 3  
Customer Concentration Risk [Member] | Accounts Receivable [Member] | Two Customers [Member]      
Concentration Risk, Percentage 80.00%    
Customer Concentration Risk [Member] | Accounts Receivable [Member] | Three Customers [Member]      
Concentration Risk, Percentage   60.00%