Revenue - Disaggregation of Revenues (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Disaggregation of Revenue
Total net sales	$ 130,053	$ 118,365	$ 400,655	$ 381,835
Rail Technologies and Services
Disaggregation of Revenue
Total net sales	73,942	63,988	228,956	209,131
Rail Technologies and Services | Rail Products
Disaggregation of Revenue
Total net sales	48,355	40,502	156,730	144,901
Rail Technologies and Services | Rail Technologies
Disaggregation of Revenue
Total net sales	25,587	23,486	72,226	64,230
Infrastructure Solutions
Disaggregation of Revenue
Total net sales	56,111	54,377	171,699	172,704
Infrastructure Solutions | Fabricated Steel Products
Disaggregation of Revenue
Total net sales	25,810	22,138	85,754	66,109
Infrastructure Solutions | Precast Concrete Products
Disaggregation of Revenue
Total net sales	17,972	15,745	50,723	42,816
Infrastructure Solutions | Coatings and Measurement
Disaggregation of Revenue
Total net sales	$ 12,329	$ 16,494	$ 35,222	$ 63,779