Investments (Details) (USD $)	3 Months Ended		9 Months Ended
	Jan. 25, 2014	Jan. 26, 2013	Jan. 25, 2014	Jan. 26, 2013	Apr. 27, 2013
Schedule of Available-for-sale Securities [Line Items]
Amount of investment which enhance return on cash	$ 37,900,000		$ 37,900,000		$ 29,900,000
Summary of investments [Abstract]
Gross Unrealized Gains	1,294,000		1,294,000		456,000
Gross Unrealized Losses	(585,000)		(585,000)		(156,000)
Fair Value	53,983,000		53,983,000		41,090,000
Sales of available-for-sale securities [Abstract]
Proceeds from sales	9,778,000	6,973,000	27,974,000	11,881,000
Gross realized gains	775,000	2,163,000	820,000	3,008,000
Gross realized losses	(473,000)	(106,000)	(538,000)	(142,000)
Available-for-sale fair value by contractual maturity [Abstract]
Available-for-sale securities, within one year, fair value	10,500,000		10,500,000
Available-for-sale Securities, within two through five years, fair value	31,300,000		31,300,000
Available-for-sale securities, within six through ten years, fair value	1,800,000		1,800,000
Available-for-sale securities, after ten years, fair value	600,000		600,000
Other Current Assets [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale investments, current	10,500,000		10,500,000		10,800,000
Trading securities, current	1,600,000		1,600,000		1,100,000
Other Long-Term Assets [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale investments	41,900,000		41,900,000		29,200,000
Equity Securities [Member]
Summary of investments [Abstract]
Gross Unrealized Gains	1,121,000		1,121,000		296,000
Gross Unrealized Losses	(66,000)		(66,000)		(152,000)
Fair Value	8,073,000		8,073,000		6,668,000
Fixed Income [Member]
Summary of investments [Abstract]
Gross Unrealized Gains	172,000		172,000		159,000
Gross Unrealized Losses	(509,000)		(509,000)		(1,000)
Fair Value	44,192,000		44,192,000		33,076,000
Mutual Funds [Member]
Summary of investments [Abstract]
Gross Unrealized Gains	0		0		0
Gross Unrealized Losses	0		0		0
Fair Value	1,604,000		1,604,000		1,126,000
Other [Member]
Summary of investments [Abstract]
Gross Unrealized Gains	1,000		1,000		1,000
Gross Unrealized Losses	(10,000)		(10,000)		(3,000)
Fair Value	$ 114,000		$ 114,000		$ 220,000