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Joint Ventures (Details) - USD ($) $ in Millions | 12 Months Ended |
--- | --- | ---
Dec. 31, 2017 | Dec. 31, 2016 | Dec. 31, 2015 | Dec. 31, 2014
Schedule of Equity Method Investments [Line Items] |  |  |  |
Cash and cash equivalents | $ 141.6 | $ 229.6 | $ 149.8 | $ 269.5
Related party accounts receivable | 1.2 | 1.5 |  |
Undistributed earnings of investees accounted for under equity method | $ 10.0 |  |  |
Shanghai STAL Precision Stainless Steel Co Ltd [Member] |  |  |  |
Schedule of Equity Method Investments [Line Items] |  |  |  |
Joint venture ownership percentage | 60.00% |  |  |
Cash and cash equivalents | $ 26.2 |  |  |
Next Gen Alloys LLC [Member] |  |  |  |
Schedule of Equity Method Investments [Line Items] |  |  |  |
Joint venture ownership percentage | 51.00% |  |  |
Cash and cash equivalents | $ 7.0 |  |  |
Uniti [Member] |  |  |  |
Schedule of Equity Method Investments [Line Items] |  |  |  |
Equity method investment ownership percentage | 50.00% |  |  |
Revenue from related parties | $ 38.6 | 20.3 | 55.4 |
China Baowu Steel Group Corporation Limited [Member] | Shanghai STAL Precision Stainless Steel Co Ltd [Member] |  |  |  |
Schedule of Equity Method Investments [Line Items] |  |  |  |
Joint venture ownership percentage by unaffiliated entity | 40.00% |  |  |
VSMPO [Member] | Uniti [Member] |  |  |  |
Schedule of Equity Method Investments [Line Items] |  |  |  |
Joint venture ownership percentage by unaffiliated entity | 50.00% |  |  |
Flat Rolled Products [Member] |  |  |  |
Schedule of Equity Method Investments [Line Items] |  |  |  |
Income (loss) from equity method investments | $ 0.6 | $ 0.5 | $ (0.1) |

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