Schedule II Valuation and Qualifying Accounts (Details) - USD ($) $ in Thousands	12 Months Ended
	Apr. 28, 2018	Apr. 29, 2017	Apr. 30, 2016
Allowance for doubtful accounts [Member]
Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Period	$ 9,342	$ 12,008	$ 7,678
Charged to Costs and Expenses	6,280	1,825	8,246
Charged to Other Accounts	0	0	1,947
Deductions	6,085	4,491	5,863
Balance at End of Period	9,537	9,342	12,008
LIFO inventory adjustment [Member]
Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Period	77,816	76,501	73,381
Charged to Costs and Expenses	4,289	1,315	3,120
Charged to Other Accounts	0	0	0
Deductions	0	0	0
Balance at End of Period	82,105	77,816	76,501
Inventory obsolescence reserve [Member]
Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Period	5,621	6,621	4,218
Charged to Costs and Expenses	22,919	18,026	15,547
Charged to Other Accounts	0	0	1,550
Deductions	23,164	19,026	14,694
Balance at End of Period	5,376	5,621	6,621
Total inventory reserve [Member]
Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Period	83,437	83,122	77,599
Charged to Costs and Expenses	27,208	19,341	18,667
Charged to Other Accounts	0	0	1,550
Deductions	23,164	19,026	14,694
Balance at End of Period	$ 87,481	$ 83,437	$ 83,122