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Summary of Significant Accounting Policies - Recent Accounting Pronouncements (Details) - USD ($) $ in Millions | 3 Months Ended | 12 Months Ended |
--- | --- | --- | ---
Mar. 31, 2018 | Dec. 31, 2018 | Dec. 31, 2017 | Jan. 01, 2018
Pro Forma [Member] | Accounting Standards Update 2017-07 [Member] |  |  |  |
New Accounting Pronouncements or Change in Accounting Principle [Line Items] |  |  |  |
Expected impact to operating results |  |  | $ 54.3 |
Forecast [Member] | Accounting Standards Update 2017-07 [Member] |  |  |  |
New Accounting Pronouncements or Change in Accounting Principle [Line Items] |  |  |  |
Expected impact to operating results | $ (6.0) |  |  |
High Performance Materials & Components [Member] | Forecast [Member] | Accounting Standards Update 2014-09 [Member] |  |  |  |
New Accounting Pronouncements or Change in Accounting Principle [Line Items] |  |  |  |
Expected impact to operating results |  | $ (5.0) |  |
Subsequent Event [Member] | High Performance Materials & Components [Member] | Accounting Standards Update 2014-09 [Member] |  |  |  |
New Accounting Pronouncements or Change in Accounting Principle [Line Items] |  |  |  |
Increase in retained earnings |  |  |  | $ 15.5
Increase in assets |  |  |  | 33.0
Increase in liabilities |  |  |  | $ 30.0

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