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Summary of Significant Accounting Policies New Accounting Pronouncements and Changes in Accounting Principals (Details) - Adjustments for New Accounting Pronouncement [Member] - USD ($) $ in Millions | 3 Months Ended | 9 Months Ended | 12 Months Ended |  |
--- | --- | --- | --- | --- | ---
Oct. 01, 2017 | Oct. 01, 2017 | Oct. 02, 2016 | Dec. 31, 2018 | Jan. 01, 2018 | Jan. 01, 2017
ASU 2016-16 [Member] | Subsequent Event [Member] |  |  |  |  |  |
New Accounting Pronouncements or Change in Accounting Principle [Line Items] |  |  |  |  |  |
Other income tax benefit (expense) |  |  |  | $ (1.5) |  |
ASU 2016-16 [Member] | Retained Earnings [Member] | Subsequent Event [Member] |  |  |  |  |  |
New Accounting Pronouncements or Change in Accounting Principle [Line Items] |  |  |  |  |  |
Estimated deferred tax assets |  |  |  |  | $ 30.0 |
ASU 2016-09 [Member] |  |  |  |  |  |
New Accounting Pronouncements or Change in Accounting Principle [Line Items] |  |  |  |  |  |
Other income tax benefit (expense) | $ 0.3 | $ 2.1 |  |  |  |
Excess tax benefit from stock-based compensation, Operating Activities |  |  | $ 2.3 |  |  |
Excess tax benefit from stock-based compensation, Financing Activities |  |  | $ 2.3 |  |  |
ASU 2016-09 [Member] | Retained Earnings [Member] |  |  |  |  |  |
New Accounting Pronouncements or Change in Accounting Principle [Line Items] |  |  |  |  |  |
Cumulative effect of new accounting principle in period of adoption |  |  |  |  |  | $ (0.2)

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