Description of the Business and Significant Accounting Policies (Segments) (Details) - segment	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Mar. 01, 2019
Segment Reporting Information
Number of reporting segments	3
Steel Operations
Segment Reporting Information
Percentage of external net sales	75.00%	74.00%
Metals Recycling Operations
Segment Reporting Information
Percentage of external net sales	13.00%	15.00%
Steel Fabrication Operations
Segment Reporting Information
Percentage of external net sales	8.00%	8.00%
United Steel Supply, LLC
Segment Reporting Information
Acquisition of interest (as a percent)			75.00%