Changes in Accounting Estimates (Details) - USD ($)	12 Months Ended
	Apr. 30, 2022	Apr. 30, 2021	Apr. 30, 2020
Compensation expense	$ 5,390,000	$ 6,932,000	$ 6,227,000
Adoption of ASU 2018-09
Compensation expense	1,602,000
TMS contract
Amount of aggregate impact of adjustments in contract estimates on revenue related to performance obligations satisfied or partially satisfied in previous periods	(1,124,000)	$ (1,041,000)
TMS contract | Revision of estimate of total costs required to complete the contracts | Cumulative catch-up adjustment
Amount of aggregate impact of adjustments in contract estimates on revenue related to performance obligations satisfied or partially satisfied in previous periods	$ (1,403,000)		(1,403,000)
Amount of aggregate impact of adjustments in contract estimates on revenue related to performance obligations satisfied or partially satisfied in previous periods increased			$ 1,099,000