Goodwill by Reporting Segment (Details) - USD ($) $ in Thousands	12 Months Ended
Mar. 31, 2017	Mar. 31, 2016
Goodwill [Roll Forward]
Goodwill, beginning balance	$ 1,012,652
Goodwill, ending balance	2,299,009	$ 1,012,652
Atmel Corporation
Goodwill [Roll Forward]
Goodwill, ending balance	1,286,371
Semiconductor products
Goodwill [Roll Forward]
Goodwill, beginning balance	993,452	552,071
Goodwill, ending balance	2,279,809	993,452
Semiconductor products \| ISSC Technologies Corporation
Goodwill [Roll Forward]
Additions due to business combination		389
Semiconductor products \| Atmel Corporation
Goodwill [Roll Forward]
Additions due to business combination	1,286,371
Semiconductor products \| Micrel Incorporated
Goodwill [Roll Forward]
Additions due to business combination		440,992
Purchase accounting adjustments	(14)
Technology licensing
Goodwill [Roll Forward]
Goodwill, beginning balance	19,200	19,200
Goodwill, ending balance	19,200	19,200
Technology licensing \| ISSC Technologies Corporation
Goodwill [Roll Forward]
Additions due to business combination		0
Technology licensing \| Atmel Corporation
Goodwill [Roll Forward]
Additions due to business combination	0
Technology licensing \| Micrel Incorporated
Goodwill [Roll Forward]
Additions due to business combination		$ 0
Purchase accounting adjustments	$ 0

Amount after accumulated impairment loss of an asset representing future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 350
-SubTopic 20
-Section 50
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=35741047&loc=d3e13816-109267

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 350
-SubTopic 20
-Section 45
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=6388280&loc=d3e13770-109266

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Amount of increase in asset representing future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized resulting from a business combination.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 350
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=35741047&loc=d3e13816-109267

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Amount of increase (decrease) from adjustments after acquisition date under purchase accounting of an asset representing the future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 805
-SubTopic 10
-Section 25
-Paragraph 16
-URI http://asc.fasb.org/extlink&oid=34752592&loc=d3e961-128460

Reference 2: http://www.xbrl.org/2003/role/presentationRef
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-Name Accounting Standards Codification
-Topic 350
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-Section 50
-Paragraph 1
-Subparagraph (g)
-URI http://asc.fasb.org/extlink&oid=35741047&loc=d3e13816-109267

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A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.

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