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Business Segments - Reconciliation of Revenue from Segments to Consolidated (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018
Segment Reporting Information
Net Sales	$ 149,379	$ 154,276	$ 200,933	$ 150,469	$ 164,531	$ 167,094	$ 172,890	$ 122,454	$ 655,057	$ 626,969
Segment Profit									36,514	38,913
Segment Assets	405,171				383,249				405,171	383,249
Depreciation/Amortization									17,631	18,593
Expenditures for Long-Lived Assets									8,831	5,251
Rail Products and Services
Segment Reporting Information
Net Sales									321,808	319,524
Construction Products
Segment Reporting Information
Net Sales									182,486	158,653
Tubular and Energy Services
Segment Reporting Information
Net Sales									150,763	148,792
Operating Segments
Segment Reporting Information
Net Sales									655,057	626,969
Segment Profit									36,514	38,913
Segment Assets	346,692				363,239				346,692	363,239
Depreciation/Amortization									16,303	17,328
Expenditures for Long-Lived Assets									8,479	4,949
Operating Segments \| Rail Products and Services
Segment Reporting Information
Net Sales									321,808	319,524
Segment Profit									19,641	19,468
Segment Assets	186,323				175,704				186,323	175,704
Depreciation/Amortization									6,469	6,810
Expenditures for Long-Lived Assets									2,293	941
Operating Segments \| Construction Products
Segment Reporting Information
Net Sales									182,486	158,653
Segment Profit									5,726	6,798
Segment Assets	83,049				97,133				83,049	97,133
Depreciation/Amortization									1,660	1,728
Expenditures for Long-Lived Assets									1,266	796
Operating Segments \| Tubular and Energy Services
Segment Reporting Information
Net Sales									150,763	148,792
Segment Profit									11,147	12,647
Segment Assets	$ 77,320				$ 90,402				77,320	90,402
Depreciation/Amortization									8,174	8,790
Expenditures for Long-Lived Assets									$ 4,920	$ 3,212