Business Acquisitions (Narrative) (Details) (USD $)	0 Months Ended	12 Months Ended			0 Months Ended
	Apr. 01, 2014	Mar. 31, 2015	Mar. 31, 2014	Mar. 31, 2013	Jul. 17, 2014
Business Acquisition [Line Items]
Business Combination, Consideration Transferred, Share-based Payment Awards	$ 1,600,000
Payments to Acquire Businesses, Net of Cash Acquired		252,469,000	0	0
ISSC Technologies Corporation [Member]
Business Acquisition [Line Items]
Percentage of interest acquired in acquisition					83.50%
Purchased price paid					267,600,000
Noncontrolling Interest, Ownership Percentage by Parent		94.10%
Deferred Tax Liabilities, Intangible Assets					25,100,000
Cash Acquired from Acquisition					42,200,000
Payments to Acquire Businesses, Net of Cash Acquired					225,400,000
Revenue of acquiree included in statement of income since the acquisition date		37,800,000
Net income (loss) of acquiree included in statement of income since the acquisition date		(25,600,000)
Supertex Inc. [Member]
Business Acquisition [Line Items]
Acquisition price per share	$ 33.00
Consideration transferred	391,800,000
Deferred Tax Liabilities, Intangible Assets	22,800,000
Cash Acquired from Acquisition	155,800,000
Payments to Acquire Businesses, Net of Cash Acquired	234,400,000
Revenue of acquiree included in statement of income since the acquisition date		$ 72,700,000