Investments (Details) (USD $)	12 Months Ended
	Apr. 25, 2015	Apr. 26, 2014	Apr. 27, 2013
Summary of investments
Gross Unrealized Gains	$ 2,239,000	$ 1,413,000
Gross Unrealized Losses	(114,000)	(106,000)
Fair Value	61,195,000	60,938,000
Sales of available-for-sale securities
Proceeds from sales	33,750,000	34,557,000	18,662,000
Gross realized gains	285,000	857,000	4,486,000
Gross realized losses	(74,000)	(559,000)	(1,316,000)
Fair value of available-for-sale securities by contractual maturity
Fair value, available-for-sale securities with contractual maturity within one year	16,900,000
Fair value, available-for-sale securities with contractual maturity within two to five years	32,000,000
Fair value, available-for-sale securities with contractual maturity within six to ten years	1,300,000
Fair value, available-for-sale securities with contractual maturity after ten years	200,000
Investments Used to Enhance Returns on Cash
Summary of investments
Fair Value	45,500,000	44,700,000
Other current assets
Investments
Available-for-sale investments	16,800,000	15,900,000
Trading securities	1,100,000	1,800,000
Other long-term assets
Investments
Available-for-sale investments	43,300,000	43,200,000
Equity securities
Summary of investments
Gross Unrealized Gains	2,014,000	1,246,000
Gross Unrealized Losses	(78,000)	(52,000)
Fair Value	9,251,000	8,216,000
Fixed income
Summary of investments
Gross Unrealized Gains	224,000	166,000
Gross Unrealized Losses	(14,000)	(44,000)
Fair Value	50,358,000	50,510,000
Mutual funds
Summary of investments
Fair Value	1,127,000	1,787,000
Other
Summary of investments
Gross Unrealized Gains	1,000	1,000
Gross Unrealized Losses	(22,000)	(10,000)
Fair Value	$ 459,000	$ 425,000