Business Acquisitions (Details) (USD $)	6 Months Ended	12 Months Ended
	Sep. 30, 2010	Mar. 31, 2011	Mar. 31, 2010	Mar. 31, 2009	Apr. 08, 2010	Mar. 08, 2010
Notes to Financial Statements [Abstract]
Number of completed business acquisition(s) (in number of acquisitions)		2	1	3
Liabilities assumed [Abstract]
Bankruptcy reorganization liability		$ 19,400,000
Business Acquisition, Pro Forma Information [Abstract]
Amount of contingent consideration payments made to the previous owners of R and E international		12,100,000
Amount of derecognition of negative goodwill recorded on the acquisition		2,400,000
Business Acquisitions [Member]
Business Acquisition, Cost of Acquired Entity, Purchase Price [Abstract]
Total cash consideration paid		6,500,000	9,300,000	19,900,000
Estimated fair value of contingent consideration		2,000,000	1,300,000
Assets acquired [Abstract]
Cash and cash equivalents		2,500,000
Goodwill		1,000,000	4,200,000	4,300,000
Purchased intangible assets		5,600,000	7,000,000	15,100,000
Liabilities assumed [Abstract]
Acquired Finite-lived Intangible Asset, Weighted Average Useful Life		7
Amount of escrowed cash included in other current assets on balance sheet		19,400,000
Silicon Storage Technology, Inc. acquisition [Member]
Business Acquisition, Cost of Acquired Entity, Purchase Price [Abstract]
Price per share at fair value (in amount per share)					$ 3.05
Total purchase price					353,844,000
Total cash consideration paid					295,400,000	58,400,000
Contingent liaibilities recorded at acquisition date					13,000,000
Assets acquired [Abstract]
Cash and cash equivalents					182,735,000
Short-term investments					12,069,000
Accounts receivable, net					44,820,000
Inventories					39,962,000
Deferred tax assets					21,785,000
Other current assets					3,768,000
Long-term investments					54,342,000
Property, plant and equipment, net					6,623,000
Non-marketable equity investments					15,772,000
Other assets					3,634,000
Goodwill					24,961,000
Purchased intangible assets					50,930,000
Assets held for sale					23,761,000
Total assets acquired					485,162,000
Liabilities assumed [Abstract]
Accounts payable					(28,906,000)
Accrued liabilities					(40,914,000)
Deferred income on shipments to distributors					(2,322,000)
Long-term income tax payable					(36,587,000)
Deferred tax liability					(17,599,000)
Other liabilities					(4,990,000)
Total liabilities assumed					(131,318,000)
Purchase price allocated					353,844,000
Net deferred tax liability related to future amortization of intangible assets					2,000,000
Continuing revenue related to acquisition included in consolidated statements of income	114,900,000	228,300,000
Continuing earnings related to acquisition included in consolidated statements of income	17,400,000
Business Acquisition, Pro Forma Information [Abstract]
Total revenue		1,494,727,000	1,190,178,000	1,145,099,000
Net income		429,794,000	207,421,000	233,925,000
Basic earnings per share		$ 2.30	$ 1.13	$ 1.28
Diluted earnings per share		$ 2.21	$ 1.11	$ 1.25
Core/developed technology [Member]
Assets acquired [Abstract]
Purchased intangible assets					32,900,000
Liabilities assumed [Abstract]
Useful life minimum		5
Useful life maximum		10
In-process research and development [Member]
Assets acquired [Abstract]
Purchased intangible assets			2,900,000		900,000
Trademarks and trade names [Member]
Assets acquired [Abstract]
Purchased intangible assets					1,730,000
Customer-related [Member]
Assets acquired [Abstract]
Purchased intangible assets					13,100,000
Backlog [Member]
Assets acquired [Abstract]
Purchased intangible assets					2,300,000
Semiconductor products [Member]
Assets acquired [Abstract]
Goodwill					5,800,000
Technology licensing [Member]
Assets acquired [Abstract]
Goodwill					$ 19,200,000