Changes in Accounting Estimates (Details) - Revision of estimate of total costs required to complete the contracts - Cumulative catch-up adjustment - USD ($) $ in Thousands	12 Months Ended
	Apr. 30, 2020	Apr. 30, 2018
Amount of revised aggregate impact of adjustments in contract estimates on revenue related to performance obligations satisfied or partially satisfied in previous periods		$ 1,255
Design and development agreement
Amount of aggregate impact of adjustments in contract estimates on revenue related to performance obligations satisfied or partially satisfied in previous periods	$ 1,099
TMS contract
Amount of aggregate impact of adjustments in contract estimates on revenue related to performance obligations satisfied or partially satisfied in previous periods	$ (1,403)