Business Segment - Sales by Major Product Line (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
Revenue from External Customer
Net Sales	$ 149,379	$ 154,276	$ 200,933	$ 150,469	$ 164,531	$ 167,094	$ 172,890	$ 122,454	$ 655,057	$ 626,969
Rail Products
Revenue from External Customer
Net Sales									194,464	188,590
Rail Technologies
Revenue from External Customer
Net Sales									127,344	130,934
Piling and Fabricated Bridges Products
Revenue from External Customer
Net Sales									114,076	102,246
Protective Coating and Measurement Systems
Revenue from External Customer
Net Sales									99,760	89,026
Test , Inspection and Threading Services
Revenue from External Customer
Net Sales									68,410	56,407
Precast Concrete Products
Revenue from External Customer
Net Sales									$ 51,003	$ 59,766