Description of the Business and Significant Accounting Policies - Segments (Details)	3 Months Ended
	Mar. 31, 2016 segment item facility	Mar. 31, 2015
Segment Reporting Information
Number of reporting segments | segment	3
Steel Operations
Segment Reporting Information
Number of downstream coating facilities | facility	10
Percentage of external net sales	70.00%	68.00%
Metals Recycling Operations
Segment Reporting Information
Percentage of external net sales	15.00%	21.00%
Steel Fabrication Operations
Segment Reporting Information
Percentage of external net sales	10.00%	8.00%
Number of New Millennium Building Systems' joist and deck plants | item	8