Business Segments (Reconciliation of Operating Profit (Loss) from Segments to Consolidated) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Segment Reporting [Abstract]
Profit (loss) for reportable segments	$ 8,511	$ (124,207)	$ 10,711	$ (124,945)
Interest expense	(2,181)	(1,652)	(4,289)	(2,822)
Interest income	54	52	110	107
Other income (expense)	18	(107)	13	(822)
LIFO (expense) income	(192)	452	(181)	525
Equity in income (loss) of nonconsolidated investments	145	(487)	(55)	(683)
Corporate expense, cost of capital elimination, and other unallocated charges	(2,856)	(3,476)	(4,801)	(4,934)
Income (loss) before income taxes	$ 3,499	$ (129,425)	$ 1,508	$ (133,574)