Revenue - Disaggregation of Revenues (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Disaggregation of Revenue
Total net sales	$ 154,522	$ 141,563	$ 270,602	$ 263,470
Rail Technologies and Services
Disaggregation of Revenue
Total net sales	88,782	74,939	155,014	145,143
Rail Technologies and Services | Rail Products
Disaggregation of Revenue
Total net sales	64,565	56,500	108,375	104,399
Rail Technologies and Services | Rail Technologies
Disaggregation of Revenue
Total net sales	24,217	18,439	46,639	40,744
Infrastructure Solutions
Disaggregation of Revenue
Total net sales	65,740	66,624	115,588	118,327
Infrastructure Solutions | Fabricated Steel Products
Disaggregation of Revenue
Total net sales	32,223	25,580	59,944	43,971
Infrastructure Solutions | Precast Concrete Products
Disaggregation of Revenue
Total net sales	20,073	16,428	32,751	27,071
Infrastructure Solutions | Coatings and Measurement
Disaggregation of Revenue
Total net sales	$ 13,444	$ 24,616	$ 22,893	$ 47,285