Investments (Details) (USD $)	12 Months Ended
	Apr. 27, 2013	Apr. 28, 2012	Apr. 30, 2011
Schedule of Investments [Line Items]
Amount of investment which enhance return on cash	$ 29,900,000
Defined benefit and deferred compensation plan investments	11,200,000
Summary of investments [Abstract]
Gross Unrealized Gains	456,000	2,908,000
Gross Unrealized Losses	(156,000)	(90,000)
Fair Value	41,090,000	11,200,000
Sales of available-for-sale securities [Abstract]
Proceeds from sales	18,662,000	5,622,000	7,448,000
Gross realized gains	4,486,000	573,000	592,000
Gross realized losses	(1,316,000)	(54,000)	(63,000)
Available-for-sale fair value by contractual maturity [Abstract]
Available-for-sale securities, within one year, fair value	10,800,000
Available-for-sale Securities, within two through five years, fair value	20,800,000
Available-for-sale securities, within six through ten years, fair value	1,000,000
Available-for-sale securities, after ten years, fair value	500,000
Other Current Assets [Member]
Schedule of Investments [Line Items]
Available-for-sale investments, current	10,800,000
Trading securities, current	1,100,000
Other Long-Term Assets [Member]
Schedule of Investments [Line Items]
Available-for-sale investments	29,200,000	10,200,000
Trading securities		1,000,000
Equity Securities [Member]
Summary of investments [Abstract]
Gross Unrealized Gains	296,000	2,806,000
Gross Unrealized Losses	(152,000)	(83,000)
Fair Value	6,668,000	7,237,000
Fixed Income [Member]
Summary of investments [Abstract]
Gross Unrealized Gains	159,000	102,000
Gross Unrealized Losses	(1,000)	(7,000)
Fair Value	33,076,000	2,850,000
Mutual Funds [Member]
Summary of investments [Abstract]
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	0
Fair Value	1,126,000	950,000
Other [Member]
Summary of investments [Abstract]
Gross Unrealized Gains	1,000	0
Gross Unrealized Losses	(3,000)	0
Fair Value	$ 220,000	$ 163,000