Costs and Estimated Earnings in Excess of Billings, Net (Details) - Costs and Estimated Earnings in Excess of Billings, Net - USD ($) $ in Thousands	Apr. 30, 2021	Apr. 30, 2020
Costs and Estimated Earnings in Excess of Billings, Net [Abstract]
Costs and estimated earnings in excess of billings	$ 12,640	$ 10,460
Billings in excess of costs and estimated earnings	(10,692)	(3,507)
Net asset	$ 1,948	$ 6,953