Goodwill by Reporting Segment (Details) (USD $)								6 Months Ended					6 Months Ended
	Sep. 30, 2014	Mar. 31, 2014	Sep. 30, 2014 Supertex Inc. [Member]	Jun. 30, 2014 Supertex Inc. [Member]	Jul. 17, 2014 ISSC Technologies Corporation [Member]	Sep. 30, 2014 Semiconductor products [Member]	Mar. 31, 2014 Semiconductor products [Member]	Sep. 30, 2014 Semiconductor products [Member] Supertex Inc. [Member]	Sep. 30, 2014 Semiconductor products [Member] ISSC Technologies Corporation [Member]	Sep. 30, 2014 Semiconductor products [Member] Other acquisitions	Sep. 30, 2014 Technology licensing [Member]	Mar. 31, 2014 Technology licensing [Member]	Sep. 30, 2014 Technology licensing [Member] Supertex Inc. [Member]	Sep. 30, 2014 Technology licensing [Member] ISSC Technologies Corporation [Member]	Sep. 30, 2014 Technology licensing [Member] Other acquisitions
Goodwill [Roll Forward]
Goodwill, beginning balance	$ 557,965,000	$ 276,097,000	$ 132,508,000	$ 133,713,000	$ 152,243,000	$ 538,765,000	$ 256,897,000				$ 19,200,000	$ 19,200,000
Additions due to business combination								132,508,000	152,243,000	625,000			0	0	0
Goodwill, Translation Adjustments									(3,508,000)					0
Goodwill, ending balance	$ 557,965,000	$ 276,097,000	$ 132,508,000	$ 133,713,000	$ 152,243,000	$ 538,765,000	$ 256,897,000				$ 19,200,000	$ 19,200,000