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Environmnetal Matters - Narrative (Details) $ in Millions	12 Months Ended
	Apr. 28, 2018 USD ($)	Apr. 29, 2017 USD ($)	Apr. 30, 2016 USD ($)
Site Contingency [Line Items]
Number of plant sites subject to environmental investigation and/or remediation	2
Accruals for environmental matters	$ 1.1	$ 1.3
Spent on remediation clean-ups and related studies	0.3	1.2	$ 1.0
Other accrued expenses
Site Contingency [Line Items]
Accruals for environmental matters	$ 0.8	$ 0.8

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Site Contingency, Number of Sites Subject to Environmental Investigation or Remediation

+ References

No definition available.

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- Definition

Total costs accrued as of the balance sheet date for environmental loss contingencies.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 450
-SubTopic 20
-Section 50
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=82911808&loc=d3e14326-108349

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 410
-SubTopic 30
-Section 50
-Paragraph 7
-URI http://asc.fasb.org/extlink&oid=6393242&loc=d3e13207-110859

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-Name Accounting Standards Codification
-Topic 450
-SubTopic 20
-Section 25
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The charge against earnings in the period for known or estimated future costs arising from requirements to perform environmental remediation activities.

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Reference 1: http://www.xbrl.org/2003/role/presentationRef
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-Name Accounting Standards Codification
-Topic 410
-SubTopic 30
-Section 50
-Paragraph 12
-URI http://asc.fasb.org/extlink&oid=6393242&loc=d3e13296-110859

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 28
-URI http://asc.fasb.org/extlink&oid=98514028&loc=d3e3602-108585

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