Stock Incentive and Purchase Plans (Allocation Of Share Based Compensation Costs By Type Of Arrangement) (Details) (USD $)	3 Months Ended		9 Months Ended
	Jan. 25, 2013	Jan. 27, 2012	Jan. 25, 2013	Jan. 27, 2012
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation	$ 2,263,234	$ 2,841,344	$ 9,109,422	$ 8,430,939
Stock options [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation	681,541	673,875	2,245,928	2,000,847
Service-based restricted stock and restricted stock unit awards [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation	970,664	1,053,475	3,974,127	4,194,361
Performance-based restricted stock and restricted stock unit and market-based awards [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation	$ 611,029	$ 1,113,994	$ 2,889,367	$ 2,235,731