Schedule II Valuation and Qualifying Accounts (Details) - USD ($) $ in Thousands	12 Months Ended
	Apr. 29, 2017	Apr. 30, 2016	Apr. 25, 2015
Allowance for doubtful accounts [Member]
Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Period	$ 12,008	$ 7,678	$ 8,322
Charged to Costs and Expenses	1,825	8,246	2,546
Charged to Other Accounts	0	1,947	0
Deductions	4,491	5,863	3,190
Balance at End of Period	9,342	12,008	7,678
LIFO inventory adjustment [Member]
Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Period	76,501	73,381	71,596
Charged to Costs and Expenses	1,315	3,120	1,785
Charged to Other Accounts	0	0	0
Deductions	0	0	0
Balance at End of Period	77,816	76,501	73,381
Inventory obsolescence reserve [Member]
Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Period	6,621	4,218	3,498
Charged to Costs and Expenses	18,026	15,547	17,624
Charged to Other Accounts	0	1,550	0
Deductions	19,026	14,694	16,904
Balance at End of Period	5,621	6,621	4,218
Total inventory reserve [Member]
Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Period	83,122	77,599	75,094
Charged to Costs and Expenses	19,341	18,667	19,409
Charged to Other Accounts	0	1,550	0
Deductions	19,026	14,694	16,904
Balance at End of Period	$ 83,437	$ 83,122	$ 77,599