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Summary of Significant Accounting Policies - Revenue Recognition, Share-Based Compensation and Foreign Currencies (Details) $ in Millions | 12 Months Ended
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Dec. 31, 2019 USD ($) item | Dec. 31, 2018 USD ($) | Dec. 31, 2017 USD ($)
Revenue Recognition |  |  |
Number of performance obligations from sales of metal products | item | 1 |  |
Shipping and handling costs included in operating expenses | $ 404.1 | $ 412.7 | $ 372.3
Share-Based Compensation |  |  |
Stock-based compensation expense | 51.2 | 45.5 | 33.4
Foreign Currencies |  |  |
Net gain (loss) resulting from foreign currency transactions | $ (4.1) | $ 0.6 | $ (4.9)
Toll processing and logistics |  |  |
Revenue Recognition |  |  |
Number Of Days To Perform Services | 1 day |  |

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