Investments (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Jan. 23, 2016	Jan. 24, 2015	Jan. 23, 2016	Jan. 24, 2015	Apr. 25, 2015
Summary of investments
Gross Unrealized Gains	$ 763		$ 763		$ 2,239
Gross Unrealized Losses	(321)		(321)		(114)
Fair Value	44,214		44,214		61,195
Sales of available-for-sale securities
Proceeds from sales	4,487	$ 6,160	23,896	$ 23,987
Gross realized gains	267	209	970	254
Gross realized losses	(18)	$ (23)	(557)	$ (53)
Fair value of available-for-sale securities by contractual maturity
Fair value, available-for-sale securities with contractual maturity within one year	12,600		12,600
Fair value, available-for-sale securities with contractual maturity within two to five years	22,200		22,200
Fair value, available-for-sale securities with contractual maturity within six to ten years	1,500		1,500
Fair value, available-for-sale securities with contractual maturity after ten years	100		100
Investments Used to Enhance Returns on Cash
Summary of investments
Fair Value	31,400		31,400		45,500
Other current assets
Investments
Available-for-sale investments	12,400		12,400		16,800
Trading securities					1,100
Other long-term assets
Investments
Available-for-sale investments	31,800		31,800		43,300
Equity securities
Summary of investments
Gross Unrealized Gains	664		664		2,014
Gross Unrealized Losses	(244)		(244)		(78)
Fair Value	7,457		7,457		9,251
Fixed income
Summary of investments
Gross Unrealized Gains	98		98		224
Gross Unrealized Losses	(56)		(56)		(14)
Fair Value	36,432		36,432		50,358
Mutual funds
Summary of investments
Fair Value					1,127
Other
Summary of investments
Gross Unrealized Gains	1		1		1
Gross Unrealized Losses	(21)		(21)		(22)
Fair Value	$ 325		$ 325		$ 459