Consolidated Statements of Cash Flows (USD $)	12 Months Ended
	Apr. 26, 2013	Apr. 27, 2012	Apr. 29, 2011
Cash Flows From Operating Activities:
Net income	$ 46,357,502	$ 36,077,732	$ 46,725,710
Non-cash items included in net income:
Depreciation	3,770,756	3,474,612	2,737,953
Amortization of intangible assets	867,613	1,228,245	554,809
Stock-based compensation	11,683,249	11,102,237	6,365,003
Deferred income taxes	22,421,044	22,666,255	1,101,763
Deferred license revenue amortization	(1,493,968)	(1,493,968)	(1,493,969)
Impairment of investment	4,058,768	0	0
Gain on warrants' liability	(1,325,574)	0	0
Unrealized loss (gain) in foreign currency transactions and other	136,344	1,808,435	(1,766,344)
Changes in operating assets and liabilities:
Accounts receivable, net	(10,184,633)	(1,247,219)	(1,952,789)
Inventories	(3,395,899)	682,445	(819,399)
Other current assets	(304,992)	(451,694)	(220,172)
Other assets	(100,080)	51,748	256,683
Accounts payable and accrued liabilities	6,563,629	1,127,337	(1,617,141)
Net cash provided by operating activities	79,053,759	75,026,165	49,872,107
Cash Flow From Investing Activities:
(Increase) decrease in restricted cash	(99,573)	0	1,000,000
Payments for short-term investments	(15,000,000)	0	0
Purchases of plant and equipment	(9,705,446)	(17,484,102)	(3,542,599)
Intangible asset purchases	(4,600,000)	(500,000)	(3,844,401)
Investment in convertible preferred stock	(6,588,201)	(4,000,000)	0
Investments in convertible debt securities	0	0	(5,000,000)
Net cash used in investing activities	(35,993,220)	(21,984,102)	(11,387,000)
Cash Flows From Financing Activities:
Proceeds from exercise of options for common stock	9,742,948	10,772,767	15,230,997
Purchase of treasury stock	(33,009,394)	(50,444,649)	(14,177,574)
Realized excess tax benefits - stock compensation based	4,416,583	0	0
Repurchase of convertible notes	0	(7,044,000)	(8,241,260)
Net cash used in financing activities	(18,849,863)	(46,715,882)	(7,187,837)
Effect of exchange rate changes on cash and cash equivalents	(156,379)	1,014,244	(1,213,331)
Net increase in cash and cash equivalents	24,054,297	7,340,425	30,083,939
Cash and cash equivalents at beginning of year	96,654,275	89,313,850	59,229,911
Cash and cash equivalents at end of year	120,708,572	96,654,275	89,313,850
Supplementary Disclosures of Cash Flow Information:
Cash paid for interest	95,729	281,206	372,939
Cash paid for income taxes	3,517,787	1,120,336	1,275,959
Supplementary Disclosures of Non-Cash Investing and Financing Activities:
Purchases of property and equipment through accounts payable and accrued liabilities	1,234,886	129,918	134,388
Reclassification from common stock warrants to warrants' liability	(3,649,637)	0	0
Reclassification from common stock warrants to treasury stock and additional paid-in-capital	(21,550,363)	0	0
PP&E and intangible assets acquired in NeuroVista foreclosure	1,450,000	0	0
Settlement of the NeuroVista note	$ (1,450,000)	$ 0	$ 0