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Segment and Geographical Area Information, Supply Information (Details) - Supplier Concentration Risk - Aluminum | 3 Months Ended | 9 Months Ended
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Sep. 30, 2017 | Sep. 30, 2016 | Sep. 30, 2017 | Sep. 30, 2016
Top five major suppliers |  |  |  |
Concentration Risk |  |  |  |
Concentration Risk, Percentage | 86.00% | 84.00% | 85.00% | 84.00%
Largest supplier |  |  |  |
Concentration Risk |  |  |  |
Concentration Risk, Percentage | 35.00% | 28.00% | 36.00% | 32.00%
Second and third largest suppliers |  |  |  |
Concentration Risk |  |  |  |
Concentration Risk, Percentage | 35.00% | 33.00% | 33.00% | 31.00%

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