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Income Taxes (Details Textual) - USD ($) $ in Millions | 3 Months Ended | 9 Months Ended | 12 Months Ended |
--- | --- | --- | --- | ---
Sep. 29, 2018 | Dec. 30, 2017 | Sep. 30, 2017 | Sep. 29, 2018 | Sep. 30, 2017 | Dec. 30, 2017 | Dec. 31, 2017
Income Tax Contingency [Line Items] |  |  |  |  |  |  |
Effective tax rate | 21.50% |  | 22.90% | 20.10% | 18.70% |  |
Federal tax rate |  |  |  |  |  | 35.00% |
Impact of tax act |  | $ 47.0 |  |  |  |  |
Toll charge |  | 49.0 |  |  |  |  |
Other than toll charge |  | $ 2.0 |  |  |  |  |
Undistributed foreign earnings |  |  |  |  |  |  | $ 12.0
Foreign Tax Authority |  |  |  |  |  |  |
Income Tax Contingency [Line Items] |  |  |  |  |  |  |
Undistributed foreign earnings |  |  |  |  |  |  | 11.8
Domestic Tax Authority |  |  |  |  |  |  |
Income Tax Contingency [Line Items] |  |  |  |  |  |  |
Undistributed foreign earnings |  |  |  |  |  |  | $ 0.2
Other Long-term Liabilities |  |  |  |  |  |  |
Income Tax Contingency [Line Items] |  |  |  |  |  |  |
Toll charge | $ 29.7 |  |  |  |  |  |
IXYS Corporation |  |  |  |  |  |  |
Income Tax Contingency [Line Items] |  |  |  |  |  |  |
Toll charge | $ (2.0) |  |  | $ 8.0 |  |  |

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