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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 |

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