Inventory (Major Classes of Inventory) (Details) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Inventory Disclosure [Abstract]
Raw materials and starting stock	$ 8,652	$ 5,769
Semi-finished and finished steel products	89,214	77,510
Operating materials	11,008	9,893
Gross inventory	108,874	93,172
Inventory reserves	(2,345)	(1,830)
Total inventory, net	$ 106,529	$ 91,342