Stock Incentive and Purchase Plans (Allocation of Share Based Compensation Costs by Expense Category) (Details) (USD $)	3 Months Ended
	Jul. 26, 2013	Jul. 27, 2012
Employee Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Stock-based compensation	$ 3,153,499	$ 4,406,533
Income tax benefit related to awards recognized in the consolidated statements of income	765,238	670,965
Total expense, net of income tax benefit	2,388,261	3,735,568
Cost of goods sold [Member]
Employee Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Stock-based compensation	98,476	188,885
Selling, general and administrative [Member]
Employee Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Stock-based compensation	2,249,166	2,778,942
Research and development [Member]
Employee Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Stock-based compensation	$ 805,857	$ 1,438,706