Note 5 - Accounts Receivable, Net, Contract Asset and Contract Liability (Details Textual) - USD ($) $ in Thousands	9 Months Ended
	Jan. 31, 2022	Jan. 31, 2021	Apr. 30, 2021
Accounts Receivable, after Allowance for Credit Loss, Total	$ 2,172		$ 1,961
Accounts Receivable, Allowance for Credit Loss, Ending Balance	143		143
Contract with Customer, Asset, after Allowance for Credit Loss, Total	1,612		$ 421
Increase (Decrease) in Contract with Customer, Asset	1,191	$ 870
Increase (Decrease) in Contract with Customer, Liability	$ (4,742)	$ 3,133