Business Segments - Reconciliation of Operating Profit (Loss) from Segments to Consolidated (Details) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Income from Operations
Interest expense - net	$ (470)	$ (3,761)	$ (4,911)	$ (6,134)
Other income (expense)		2,110	(2,919)	1,208
Income (loss) before income taxes		13,982	24,139	(24,569)
Assets
Segment Assets	370,395	370,395	405,171	383,249
Depreciation/Amortization
Depreciation/Amortization		13,579	14,389	15,032
Expenditures for Long-Lived Assets
Expenditures for Long-Lived Assets		9,179	6,026	3,658
Operating Segments
Income from Operations
Total segment profit		24,571	43,256	41,055
Interest expense - net		(3,761)	(4,911)	(6,134)
Other income (expense)		2,298	(2,919)	1,208
Concrete Tie Settlement expense (Note 18)		0	0	(43,400)
Corporate expense and other unallocated charges		(9,126)	(11,287)	(17,298)
Income (loss) before income taxes		13,982	24,139	(24,569)
Assets
Segment Assets	299,004	299,004	317,011	326,916
Depreciation/Amortization
Depreciation/Amortization		12,222	13,061	13,767
Expenditures for Long-Lived Assets
Expenditures for Long-Lived Assets		8,504	5,674	3,356
Unallocated corporate assets
Assets
Segment Assets	$ 71,391	71,391	88,160	56,333
Depreciation/Amortization
Depreciation/Amortization		1,357	1,328	1,265
Expenditures for Long-Lived Assets
Expenditures for Long-Lived Assets		$ 675	$ 352	$ 302