Customer-Funded Research & Development (Details) - USD ($)	3 Months Ended	9 Months Ended
Jan. 25, 2020	Jan. 26, 2019	Jan. 25, 2020	Jan. 26, 2019
Customer-Funded Research & Development
Revenue from customer funded research and development	$ 17,939,000	$ 19,437,000	$ 50,565,000	$ 55,344,000

The amount of compensation earned (contract income) under a research and development arrangement accounted for as a contract to perform research and development for others.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 730
-SubTopic 20
-Section 50
-Paragraph 3
-URI http://asc.fasb.org/extlink&oid=6420387&loc=d3e23221-108380

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 730
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=6420387&loc=d3e23199-108380

Name:	us-gaap_ResearchAndDevelopmentArrangementContractToPerformForOthersCompensationEarned
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration