Note 9 - Pension Plans - Contributions for All Multi-employer Pension Plans (Details) - USD ($) $ in Thousands	12 Months Ended
Apr. 28, 2018	Apr. 29, 2017	Apr. 30, 2016
Fund	$ 2,217	$ 1,940	$ 2,105
CSSS Fund [Member]
Fund	1,370	1,262	1,172
WCT Fund [Member]
Fund	619	477	485
Other Multi Employer Pension Funds [Member]
Fund	$ 228	$ 201	$ 448

Amount of contributions made to multiemployer plan by employer.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 80
-Section 50
-Paragraph 9
-URI http://asc.fasb.org/extlink&oid=65877416&loc=SL14450691-114947

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 80
-Section 50
-Paragraph 11
-URI http://asc.fasb.org/extlink&oid=65877416&loc=SL14450702-114947

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 80
-Section 50
-Paragraph 5
-Subparagraph (e)(1)
-URI http://asc.fasb.org/extlink&oid=65877416&loc=SL14450657-114947

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