Segment and Geographical Area Information, Narrative (Details)	12 Months Ended
	Dec. 31, 2017 productionfacilities customer	Dec. 31, 2016 customer	Dec. 31, 2015 customer
Segment Reporting Information
Percentage of Employees Covered by Collective Bargaining Agreements	63.00%
Percentage of Employees Covered by Collective Bargaining Agreements Expiring Within One Year	12.00%
United States
Segment Reporting Information
Number of production facilities | productionfacilities	11
Canada
Segment Reporting Information
Number of production facilities | productionfacilities	1
Customer Concentration Risk | Net sales | Largest Customer | Fabricated Products
Segment Reporting Information
Concentration risk, percentage	27.00%	26.00%	25.00%
Number of Customers | customer	1	1	1
Customer Concentration Risk | Net sales | Second Largest Customer | Fabricated Products
Segment Reporting Information
Concentration risk, percentage	12.00%	10.00%	10.00%
Customer Concentration Risk | Trade Receivables | Largest Customer
Segment Reporting Information
Concentration risk, percentage	22.00%	18.00%
Customer Concentration Risk | Trade Receivables | Second Largest Customer
Segment Reporting Information
Concentration risk, percentage	14.00%
Customer Concentration Risk | Trade Receivables | Second Largest Customer | Fabricated Products
Segment Reporting Information
Number of Customers | customer	2