Organization and Significant Accounting Policies - Contract Estimates (Details)	12 Months Ended
	Apr. 30, 2020 USD ($) contract	Apr. 30, 2018 USD ($)
Material adjustment to any one contract	$ 0
Number of active contracts | contract	1
Revision of estimate of total costs required to complete the contracts | Cumulative catch-up adjustment
Amount of revised aggregate impact of adjustments in contract estimates on revenue related to performance obligations satisfied or partially satisfied in previous periods		$ 1,255,000
Revision of estimate of total costs required to complete the contracts | Cumulative catch-up adjustment | 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	$ 1,099,000
Revision of estimate of total costs required to complete the contracts | Cumulative catch-up adjustment | TMS contract
Amount of aggregate impact of adjustments in contract estimates on revenue related to performance obligations satisfied or partially satisfied in previous periods	$ (1,403,000)