Segment Information - Summary of sale by product and service (Details) - item	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Segment Information
Number of reportable segments	1	1
Sales (as a percent)	100.00%	100.00%	100.00%
Carbon steel
Segment Information
Sales (as a percent)	52.00%	54.00%	53.00%
Aluminum
Segment Information
Sales (as a percent)	19.00%	15.00%	15.00%
Stainless steel
Segment Information
Sales (as a percent)	14.00%	14.00%	14.00%
Alloy steel
Segment Information
Sales (as a percent)	7.00%	9.00%	10.00%
Toll processing
Segment Information
Sales (as a percent)	3.00%	2.00%	2.00%
Other
Segment Information
Sales (as a percent)	5.00%	6.00%	6.00%