Revenue - Timing of Transfer (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Disaggregation of Revenue
Total net sales	$ 116,080	$ 121,907
Point in time
Disaggregation of Revenue
Total net sales	86,708	89,130
Over time
Disaggregation of Revenue
Total net sales	29,372	32,777
Rail Technologies and Services
Disaggregation of Revenue
Total net sales	66,232	70,204
Rail Technologies and Services | Point in time
Disaggregation of Revenue
Total net sales	52,044	54,888
Rail Technologies and Services | Over time
Disaggregation of Revenue
Total net sales	14,188	15,316
Infrastructure Solutions
Disaggregation of Revenue
Total net sales	49,848	51,703
Infrastructure Solutions | Point in time
Disaggregation of Revenue
Total net sales	34,664	34,242
Infrastructure Solutions | Over time
Disaggregation of Revenue
Total net sales	$ 15,184	$ 17,461