Investments (Details) (USD $)	12 Months Ended
	Apr. 26, 2014	Apr. 27, 2013	Apr. 28, 2012
Schedule of Available-for-sale Securities [Line Items]
Amount of investment which enhance return on cash	$ 44,700,000	$ 29,900,000
Summary of investments [Abstract]
Gross Unrealized Gains	1,413,000	456,000
Gross Unrealized Losses	(106,000)	(156,000)
Fair Value	60,938,000	41,090,000
Sales of available-for-sale securities [Abstract]
Proceeds from sales	34,557,000	18,662,000	8,649,000
Gross realized gains	857,000	4,486,000	573,000
Gross realized losses	(559,000)	(1,316,000)	(54,000)
Available-for-sale fair value by contractual maturity [Abstract]
Available-for-sale securities, within one year, fair value	15,900,000
Available-for-sale Securities, within two through five years, fair value	32,700,000
Available-for-sale securities, within six through ten years, fair value	1,400,000
Available-for-sale securities, after ten years, fair value	500,000
Other Current Assets [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale investments, current	15,900,000	10,800,000
Trading securities, current	1,800,000	1,100,000
Other Long-Term Assets [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale investments	43,200,000	29,200,000
Equity securities [Member]
Summary of investments [Abstract]
Gross Unrealized Gains	1,246,000	296,000
Gross Unrealized Losses	(52,000)	(152,000)
Fair Value	8,216,000	6,668,000
Fixed income [Member]
Summary of investments [Abstract]
Gross Unrealized Gains	166,000	159,000
Gross Unrealized Losses	(44,000)	(1,000)
Fair Value	50,510,000	33,076,000
Mutual funds [Member]
Summary of investments [Abstract]
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	0
Fair Value	1,787,000	1,126,000
Other [Member]
Summary of investments [Abstract]
Gross Unrealized Gains	1,000	1,000
Gross Unrealized Losses	(10,000)	(3,000)
Fair Value	$ 425,000	$ 220,000