Costs and Estimated Earnings in Excess of Billings, Net (Details) - Contracts Accounted for under Percentage of Completion [Member] - USD ($) $ in Millions	12 Months Ended
	Apr. 30, 2021	Apr. 30, 2020
Costs and Estimated Earnings in Excess of Billings, Net (Details) [Line Items]
Revenues	$ 50.2	$ 38.0
Anticipated Loss on Contracts	$ 1.0	$ 2.4