Note 8 - Shareholders' Equity (Details Textual) - USD ($) $ in Millions	6 Months Ended
Jun. 30, 2018	Dec. 30, 2017
Accumulated Other Comprehensive Income (Loss), Pension and Other Post-retirement Benefit Plans, Liability Adjustment Tax	$ 0.4	$ 1.4
Accounting Standards Update 2016-01 [Member]
Cumulative Effect on Retained Earnings, Net of Tax, Total	$ 9.8
IXYS Corporation [Member]
Stock Issued During Period, Shares, Acquisitions	2,092,491

Number of shares of stock issued during the period pursuant to acquisitions.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02(29))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.3-04)
-URI http://asc.fasb.org/extlink&oid=27012166&loc=d3e187085-122770

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02(28))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

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