Business Segments (Revenue by Product Line) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Revenues from External Customers and Long-Lived Assets
Net Sales	$ 536,377	$ 483,514	$ 624,523
Rail Technologies
Revenues from External Customers and Long-Lived Assets
Net Sales	100,257	90,469	98,237
Rail Distribution
Revenues from External Customers and Long-Lived Assets
Net Sales	90,696	83,236	126,277
Piling
Revenues from External Customers and Long-Lived Assets
Net Sales	73,158	70,535	94,853
Precast Concrete Products
Revenues from External Customers and Long-Lived Assets
Net Sales	55,877	54,514	52,044
Test and Inspection Services
Revenues from External Customers and Long-Lived Assets
Net Sales	39,198	20,765	35,906
Protective Coatings
Revenues from External Customers and Long-Lived Assets
Net Sales	38,096	23,043	33,532
Fabricated Bridge
Revenues from External Customers and Long-Lived Assets
Net Sales	32,766	20,553	29,496
Precision Measurement Systems
Revenues from External Customers and Long-Lived Assets
Net Sales	29,670	42,830	36,048
Other products
Revenues from External Customers and Long-Lived Assets
Net Sales	$ 76,659	$ 77,569	$ 118,130