Stock Incentive and Purchase Plans (Allocation Of Share Based Compensation Costs) (Details) (USD $)	3 Months Ended		9 Months Ended
	Jan. 25, 2013	Jan. 27, 2012	Jan. 25, 2013	Jan. 27, 2012
Employee Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Stock-based compensation	$ 2,263,234	$ 2,841,344	$ 9,109,422	$ 8,430,939
Cost of goods sold [Member]
Employee Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Stock-based compensation	95,940	134,953	402,450	459,493
Selling, general and administrative [Member]
Employee Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Stock-based compensation	1,635,373	1,927,393	6,096,914	6,302,349
Research and development [Member]
Employee Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Stock-based compensation	$ 531,921	$ 778,998	$ 2,610,058	$ 1,669,097