Business Segments (Reconciliation of Operating Profit (Loss) from Segments to Consolidated) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Segment Reporting [Abstract]
Profit (loss) for reportable segments	$ 9,157	$ (7,657)	$ 19,868	$ (132,602)
Interest expense	(2,026)	(1,520)	(6,315)	(4,342)
Interest income	56	50	166	157
Other income	551	1,085	564	263
LIFO (expense) income	(1,552)	917	(1,733)	1,442
Equity in income (loss) of nonconsolidated investments	50	(263)	(5)	(946)
Corporate expense, cost of capital elimination, and other unallocated charges	(3,222)	(1,973)	(8,023)	(6,907)
Income (loss) before income taxes	$ 3,014	$ (9,361)	$ 4,522	$ (142,935)