Investments (Details) (USD $)	3 Months Ended		9 Months Ended
	Jan. 26, 2013	Jan. 28, 2012	Jan. 26, 2013	Jan. 28, 2012	Apr. 28, 2012
Schedule of Investments [Line Items]
Amount of investment which enhance return on cash	$ 22,400,000		$ 22,400,000
Defined benefit and deferred compensation plan investments	11,300,000		11,300,000
Gross Unrealized Gains	573,000		573,000		2,908,000
Gross Unrealized Losses	(75,000)		(75,000)		(90,000)
Fair Value	33,703,000		33,703,000		11,200,000
Sales of Available-for-sale Securities [Abstract]
Proceeds from sales	6,973,000	1,265,000	11,881,000	4,475,000
Gross realized gains	2,163,000	92,000	3,008,000	546,000
Gross realized losses	(106,000)	(6,000)	(142,000)	(41,000)
Available-for-sale fair value by contractual maturity [Abstract]
Available-for-sale securities, within one year, fair value	6,300,000		6,300,000
Available-for-sale Securities, within two through five years, fair value	17,700,000		17,700,000
Available-for-sale securities, within six through ten years, fair value	1,000,000		1,000,000
Available-for-sale securities, after ten years, fair value	600,000		600,000
Other Current Assets [Member]
Schedule of Investments [Line Items]
Available-for-sale investments, current	6,400,000		6,400,000
Trading securities, current	1,200,000		1,200,000
Other Long-Term Assets [Member]
Schedule of Investments [Line Items]
Available-for-sale investments	26,100,000		26,100,000		10,200,000
Trading securities					1,000,000
Equity Securities [Member]
Schedule of Investments [Line Items]
Gross Unrealized Gains	446,000		446,000		2,806,000
Gross Unrealized Losses	(57,000)		(57,000)		(83,000)
Fair Value	6,426,000		6,426,000		7,237,000
Fixed Income [Member]
Schedule of Investments [Line Items]
Gross Unrealized Gains	127,000		127,000		102,000
Gross Unrealized Losses	(18,000)		(18,000)		(7,000)
Fair Value	25,619,000		25,619,000		2,850,000
Mutual Funds [Member]
Schedule of Investments [Line Items]
Gross Unrealized Gains	0		0		0
Gross Unrealized Losses	0		0		0
Fair Value	1,233,000		1,233,000		950,000
Other [Member]
Schedule of Investments [Line Items]
Gross Unrealized Gains	0		0		0
Gross Unrealized Losses	0		0		0
Fair Value	$ 425,000		$ 425,000		$ 163,000