Business Acquisitions (Narrative) (Details) (USD $)	6 Months Ended			0 Months Ended	3 Months Ended		0 Months Ended	3 Months Ended	6 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Jul. 17, 2014	Jul. 17, 2014 ISSC Technologies Corporation [Member]	Sep. 30, 2014 ISSC Technologies Corporation [Member]	Jul. 17, 2014 ISSC Technologies Corporation [Member]	Apr. 01, 2014 Supertex Inc.	Sep. 30, 2014 Supertex Inc.	Sep. 30, 2014 Supertex Inc.	Apr. 01, 2014 Supertex Inc.
Business Acquisition [Line Items]
Tendered offer price per share										$ 33.00
Percentage of interest acquired in acquisition			83.50%
Purchased price paid				$ 267,600,000
Consideration transferred							391,800,000
Non cash consideration of certain share-based payment awards							1,600,000
Cash and short-term investments acquired							155,800,000
Amount of cash paid, net of cash and short-term investments acquired	375,365,000	0					234,400,000
Net deferred tax liability for future amortization expense of acquired intangible assets						25,100,000				22,800,000
Revenue of acquiree included in statement of income since the acquisition date					16,900,000			16,600,000	34,400,000
Net income (loss) of acquiree included in statement of income since the acquisition date					$ (8,200,000)