Investments (Details) (USD $)	3 Months Ended
	Jul. 27, 2013	Jul. 28, 2012	Apr. 27, 2013
Schedule of Investments [Line Items]
Amount of investment which enhance return on cash	$ 27,800,000		$ 29,900,000
Summary of investments [Abstract]
Gross Unrealized Gains	932,000		456,000
Gross Unrealized Losses	(189,000)		(156,000)
Fair Value	39,936,000		41,090,000
Sales of available-for-sale securities [Abstract]
Proceeds from sales	8,558,000	1,428,000
Gross realized gains	13,000	224,000
Gross realized losses	(36,000)	(26,000)
Available-for-sale fair value by contractual maturity [Abstract]
Available-for-sale securities, within one year, fair value	5,600,000
Available-for-sale Securities, within two through five years, fair value	23,800,000
Available-for-sale securities, within six through ten years, fair value	600,000
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	5,600,000		10,800,000
Trading securities, current	2,000,000		1,100,000
Other Long-Term Assets [Member]
Schedule of Investments [Line Items]
Available-for-sale investments	32,300,000		29,200,000
Equity Securities [Member]
Summary of investments [Abstract]
Gross Unrealized Gains	834,000		296,000
Gross Unrealized Losses	(113,000)		(152,000)
Fair Value	7,247,000		6,668,000
Fixed Income [Member]
Summary of investments [Abstract]
Gross Unrealized Gains	97,000		159,000
Gross Unrealized Losses	(70,000)		(1,000)
Fair Value	30,460,000		33,076,000
Mutual Funds [Member]
Summary of investments [Abstract]
Gross Unrealized Gains	0		0
Gross Unrealized Losses	0		0
Fair Value	1,983,000		1,126,000
Other [Member]
Summary of investments [Abstract]
Gross Unrealized Gains	1,000		1,000
Gross Unrealized Losses	(6,000)		(3,000)
Fair Value	$ 246,000		$ 220,000