Business Segments (Reconciliation of Operating Profit (Loss) from Segments to Consolidated) (Details) - USD ($) $ in Thousands	3 Months Ended						12 Months Ended
	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017
Income from Operations
Profit for reportable segments							$ 38,913	$ 28,601
Interest expense							(6,154)	(8,070)
Other income							461	373
LIFO expense							(43,400)	0
Corporate expense, cost of capital eliminations, and other unallocated charges							(16,531)	(10,853)
(Loss) income before income taxes	$ 6,426	$ 6,162	$ (1,333)	$ 4,566	$ 3,691	$ (2,002)	(26,711)	10,051
Assets
Assets							383,249	401,743
Depreciation/Amortization
Depreciation/Amortization							18,593	19,841
Expenditures for Long-Lived Assets
Expenditures for Long-Lived Assets							5,251	6,149
Operating Segments
Income from Operations
Profit for reportable segments							38,913	28,601
Assets
Assets							363,239	375,898
Depreciation/Amortization
Depreciation/Amortization							17,328	18,369
Expenditures for Long-Lived Assets
Expenditures for Long-Lived Assets							4,949	5,587
Unallocated corporate assets
Assets
Assets							20,010	25,845
Depreciation/Amortization
Depreciation/Amortization							1,265	1,472
Expenditures for Long-Lived Assets
Expenditures for Long-Lived Assets							$ 302	$ 562