Business Segments (Significant Reconciling Items) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income (loss) from Operations:
Profit (loss) for reportable segments	$ 27,685	$ (134,165)	$ (41,349)
Interest expense	(8,377)	(6,551)	(4,378)
Interest income	307	228	206
Other income	367	1,523	5,585
LIFO (expense) income	(2,009)	2,643	2,468
Equity in income (loss) of nonconsolidated investments	6	(1,290)	(413)
Corporate expense, cost of capital elimination, and other unallocated charges	(9,937)	(9,557)	(12,696)
Income (loss) before income taxes	8,042	(147,169)	(50,577)
Assets:
Segment Assets	396,556	393,023	566,660
Depreciation/Amortization	19,841	23,492	26,674
Expenditures for Long-Lived Assets	6,149	7,664	15,201
Operating Segments
Income (loss) from Operations:
Profit (loss) for reportable segments	27,685	(134,165)	(41,349)
Assets:
Segment Assets	375,898	355,129	544,272
Depreciation/Amortization	18,369	22,176	25,675
Expenditures for Long-Lived Assets	5,587	5,353	9,836
Corporate
Assets:
Segment Assets	25,845	41,072	28,209
Depreciation/Amortization	1,472	1,316	999
Expenditures for Long-Lived Assets	562	2,311	5,077
Reconciling Items
Assets:
Segment Assets	(5,187)	(3,178)	(5,821)
Expenditures for Long-Lived Assets	$ 0	$ 0	$ 288