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Business, Product and Geographical Area Information and Concentration of Risk - Schedule of net sales by end market segment applications (Details) - USD ($) $ in Millions | 3 Months Ended | 12 Months Ended
--- | --- | ---
Dec. 31, 2019 | Sep. 30, 2019 | Jun. 30, 2019 | Mar. 31, 2019 | Dec. 31, 2018 | Sep. 30, 2018 | Jun. 30, 2018 | Mar. 31, 2018 | Dec. 31, 2019 | Dec. 31, 2018 | Dec. 31, 2017
Revenue from External Customer |  |  |  |  |  |  |  |  |  |  |
Net sales | $ 368.7 | $ 374.9 | $ 375.3 | $ 395.2 | $ 389.4 | $ 393.1 | $ 415.4 | $ 388.0 | $ 1,514.1 | $ 1,585.9 | $ 1,397.5
Aero/HS products |  |  |  |  |  |  |  |  |  |  |
Revenue from External Customer |  |  |  |  |  |  |  |  |  |  |
Net sales |  |  |  |  |  |  |  |  | 803.2 | 739.4 | 653.7
Automotive Extrusions |  |  |  |  |  |  |  |  |  |  |
Revenue from External Customer |  |  |  |  |  |  |  |  |  |  |
Net sales |  |  |  |  |  |  |  |  | 190.5 | 239.3 | 217.3
GE products |  |  |  |  |  |  |  |  |  |  |
Revenue from External Customer |  |  |  |  |  |  |  |  |  |  |
Net sales |  |  |  |  |  |  |  |  | 480.1 | 546.0 | 476.2
Other products |  |  |  |  |  |  |  |  |  |  |
Revenue from External Customer |  |  |  |  |  |  |  |  |  |  |
Net sales |  |  |  |  |  |  |  |  | 40.3 | 61.2 | $ 50.3
Transferred at Point in Time |  |  |  |  |  |  |  |  |  |  |
Revenue from External Customer |  |  |  |  |  |  |  |  |  |  |
Net sales |  |  |  |  |  |  |  |  | 866.9 | 912.7 |
Transferred over Time |  |  |  |  |  |  |  |  |  |  |
Revenue from External Customer |  |  |  |  |  |  |  |  |  |  |
Net sales |  |  |  |  |  |  |  |  | $ 647.2 | 673.2 |
Previously reported | Transferred at Point in Time |  |  |  |  |  |  |  |  |  |  |
Revenue from External Customer |  |  |  |  |  |  |  |  |  |  |
Net sales |  |  |  |  |  |  |  |  |  | 543.0 |
Previously reported | Transferred over Time |  |  |  |  |  |  |  |  |  |  |
Revenue from External Customer |  |  |  |  |  |  |  |  |  |  |
Net sales |  |  |  |  |  |  |  |  |  | $ 1,042.9 |

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