Summary of Significant Accounting Policies - Inventory (Details) - USD ($) $ in Thousands	12 Months Ended
Apr. 28, 2018	Apr. 29, 2017	Apr. 30, 2016
Accounting Policies [Abstract]
Inventories valued at LIFO as % of total inventories	84.00%	84.00%
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
LIFO inventory reserve	$ (82,105)	$ (77,816)
Increase to pre-tax income	179,263	$ 250,881	$ 301,693
Change in LIFO Calculation Method
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
LIFO inventory reserve	1,800
Increase to pre-tax income	$ 1,800

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Amount of income (loss) from continuing operations, including income (loss) from equity method investments, before deduction of income tax expense (benefit), and income (loss) attributable to noncontrolling interest.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 940
-SubTopic 20
-Section 25
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=68072869&loc=d3e41242-110953

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 225
-SubTopic 10
-Section S99
-Paragraph 2
-Subparagraph (SX 210.5-03(10))
-URI http://asc.fasb.org/extlink&oid=63488584&loc=d3e20235-122688

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-Publisher FASB
-Name Accounting Standards Codification
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-Section S99
-Paragraph 1
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Reference 4: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 225
-Section S99
-Paragraph 1
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-URI http://asc.fasb.org/extlink&oid=6879464&loc=d3e573970-122913

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Amount by which inventory stated at last-in first-out (LIFO) is less than (in excess of) inventory stated at other inventory cost methods.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.6(c))
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The percentage of LIFO (last in first out) inventory to total inventory as of the balance sheet date if other than 100 percent.

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