Revenue - Timing of Transfer (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
Point in time
Disaggregation of Revenue
Total net sales	83,477	80,249	281,533	275,396
Over time
Disaggregation of Revenue
Total net sales	46,576	38,116	119,122	106,439
Rail Technologies and Services
Disaggregation of Revenue
Total net sales	73,942	63,988	228,956	209,131
Rail Technologies and Services | Point in time
Disaggregation of Revenue
Total net sales	54,470	47,027	178,225	163,190
Rail Technologies and Services | Over time
Disaggregation of Revenue
Total net sales	19,472	16,961	50,731	45,941
Infrastructure Solutions
Disaggregation of Revenue
Total net sales	56,111	54,377	171,699	172,704
Infrastructure Solutions | Point in time
Disaggregation of Revenue
Total net sales	29,007	33,222	103,308	112,206
Infrastructure Solutions | Over time
Disaggregation of Revenue
Total net sales	$ 27,104	$ 21,155	$ 68,391	$ 60,498