Inventories, net (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Inventory, Net
Raw materials	$ 40,100	$ 50,800
Production materials, stores and supplies	13,400	12,000
Finished and in-process goods	114,300	109,800
Subtotal	167,800	172,600
Less: excess of cost over LIFO cost	(7,800)	(21,400)
Inventories, net	$ 160,000	$ 151,200
Percentage of LIFO inventory	66.00%	68.00%
Decrease in inventory	$ 0	$ 3,600	$ 0