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Note 3 - Accounts Receivable (Details Textual)
$ in Thousands
3 Months Ended 12 Months Ended
Apr. 30, 2020
USD ($)
Apr. 30, 2019
Jan. 31, 2020
USD ($)
Accounts Receivable, Outstanding for Several Years $ 4,100   $ 4,100
Retention Receivable 3,600   $ 3,600
Proceeds from Collection of Accounts Receivable Outstanding for Several Years 500    
Allowance for Doubtful Accounts Receivable Outstanding for Several Years $ 0    
Revenue Benchmark [Member] | Customer Concentration Risk [Member]      
Number of Major Customers 0 0  
Accounts Receivable [Member] | Customer Concentration Risk [Member]      
Number of Major Customers 1   1
Accounts Receivable [Member] | Customer Concentration Risk [Member] | One Customer [Member]      
Concentration Risk, Percentage 15.00%   13.30%
Other Noncurrent Assets [Member]      
Retention Receivable $ 2,200   $ 2,100