Condensed Consolidated Statements Of Cash Flows (USD $)	9 Months Ended
	Jan. 25, 2013	Jan. 27, 2012
Cash Flow From Operating Activities:
Net income	$ 34,825,431	$ 25,414,512
Non-cash items included in net income:
Depreciation	2,807,785	2,515,066
Amortization of intangible assets	633,229	1,056,917
Stock-based compensation	9,109,422	8,430,939
Deferred income taxes	16,388,319	15,671,383
Deferred license revenue amortization	(1,120,476)	(1,120,476)
Impairment of investment in NeuroVista	4,058,768	0
Gain on warrants' liability	(1,325,574)	0
Unrealized loss in foreign currency transactions and other	154,629	1,867,503
Changes in operating assets and liabilities:
Accounts receivable, net	(6,225,989)	1,117,222
Inventories	(3,044,106)	1,124,147
Other current assets	723,698	(570,475)
Other assets	(989)	51,196
Accounts payable and accrued liabilities	(1,278,862)	(2,821,873)
Net cash provided by operating activities	55,705,285	52,736,061
Cash Flow From Investing Activities:
Short-term investments	(15,000,000)
Investment in convertible preferred stock	(2,588,200)	(4,000,000)
Intangible asset purchases	(2,500,000)	(500,000)
Purchases of property, plant and equipment	(6,515,509)	(16,586,464)
Net cash used in investing activities	(26,603,709)	(21,086,464)
Cash Flow From Financing Activities:
Proceeds from exercise of options for common stock	8,969,626	2,041,546
Purchase of treasury stock	(20,105,481)	(38,815,838)
Retirement of convertible notes		(7,044,000)
Realized excess tax benefits - stock compensation based	2,040,699
Net cash used in financing activities	(9,095,156)	(43,818,292)
Effect of exchange rate changes on cash and cash equivalents	(129,525)	991,576
Net increase (decrease) in cash and cash equivalents	19,876,895	(11,177,119)
Cash and cash equivalents at beginning of period	96,654,275	89,313,850
Cash and cash equivalents at end of period	116,531,170	78,136,731
Supplementary Disclosures of Cash Flow Information:
Cash paid for interest	83,225	240,688
Cash paid for income taxes	2,060,495	886,198
Supplementary Disclosures of Non-Cash Investing and Financing Activities:
Purchases of plant and equipment in accounts payable and accrued liabilities	269,624	240,973
Reclassification from common stock warrants to warrants' liability	(3,649,637)
Reclassification from common stock warrants to additional paid-in-stock	(13,200,000)
Reclassification from common stock warrants to APIC	$ (21,550,363)