Organization and Significant Accounting Policies - Contract Estimates (Details)	3 Months Ended		9 Months Ended
	Jan. 25, 2020 USD ($) contract	Jan. 26, 2019 USD ($) contract	Jan. 25, 2020 USD ($) contract	Jan. 26, 2019 USD ($) contract
Material adjustment to any one contract	$ 0			$ 0
Number of active contracts | contract	1	1	1	1
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	$ 1,152,000		$ 1,169,000
TMS contract
Amount of aggregate impact of adjustments in contract estimates on revenue related to performance obligations satisfied or partially satisfied in previous periods		$ 1,705,000
Revision of estimate of total costs required to complete the contracts | Cumulative catch-up adjustment | Design and development agreement
Amount of revised aggregate impact of adjustments in contract estimates on revenue related to performance obligations satisfied or partially satisfied in previous periods	1,036,000		1,036,000
Revision of estimate of total costs required to complete the contracts | Cumulative catch-up adjustment | TMS contract
Amount of revised aggregate impact of adjustments in contract estimates on revenue related to performance obligations satisfied or partially satisfied in previous periods	$ 1,519,000		$ 1,519,000