Investments (Details) - USD ($) $ in Thousands	3 Months Ended
	Jul. 25, 2015	Jul. 26, 2014	Apr. 25, 2015
Summary of investments
Gross Unrealized Gains	$ 1,864		$ 2,239
Gross Unrealized Losses	(185)		(114)
Fair Value	51,138		61,195
Sales of available-for-sale securities
Proceeds from sales	12,983	$ 10,422
Gross realized gains	677	14
Gross realized losses	(506)	$ (8)
Fair value of available-for-sale securities by contractual maturity
Fair value, available-for-sale securities with contractual maturity within one year	12,100
Fair value, available-for-sale securities with contractual maturity within two to five years	28,700
Fair value, available-for-sale securities with contractual maturity within six to ten years	1,500
Fair value, available-for-sale securities with contractual maturity after ten years	200
Investments Used to Enhance Returns on Cash
Summary of investments
Fair Value	37,000		45,500
Other current assets
Investments
Available-for-sale investments	11,700		16,800
Trading securities			1,100
Other long-term assets
Investments
Available-for-sale investments	39,400		43,300
Equity securities
Summary of investments
Gross Unrealized Gains	1,737		2,014
Gross Unrealized Losses	(113)		(78)
Fair Value	8,367		9,251
Fixed income
Summary of investments
Gross Unrealized Gains	126		224
Gross Unrealized Losses	(52)		(14)
Fair Value	42,460		50,358
Mutual funds
Summary of investments
Fair Value	7		1,127
Other
Summary of investments
Gross Unrealized Gains	1		1
Gross Unrealized Losses	(20)		(22)
Fair Value	$ 304		$ 459