Description of the Business and Significant Accounting Policies - Segments (Details)	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016 segment item facility	Jun. 30, 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	72.00%	69.00%	71.00%	68.00%
Metals Recycling Operations
Segment Reporting Information
Percentage of external net sales	15.00%	20.00%	15.00%	20.00%
Steel Fabrication Operations
Segment Reporting Information
Percentage of external net sales	8.00%	8.00%	9.00%	8.00%
Number of New Millennium Building Systems' joist and deck plants | item			8