Revenue - Timing of Transfer (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Disaggregation of Revenue
Total net sales	$ 115,576	$ 118,365	$ 141,563	$ 121,907	$ 141,331	$ 144,848	$ 190,701	$ 139,548	$ 497,411	$ 616,428	$ 581,064
Point in time
Disaggregation of Revenue
Total net sales									351,391	429,653	417,811
Over time
Disaggregation of Revenue
Total net sales									146,020	186,775	163,253
Rail Technologies and Services
Disaggregation of Revenue
Total net sales									276,447	321,808	319,524
Rail Technologies and Services | Point in time
Disaggregation of Revenue
Total net sales									212,212	240,047	232,814
Rail Technologies and Services | Over time
Disaggregation of Revenue
Total net sales									64,235	81,761	86,710
Infrastructure Solutions
Disaggregation of Revenue
Total net sales									220,964	294,620	261,540
Infrastructure Solutions | Point in time
Disaggregation of Revenue
Total net sales									139,179	189,606	184,997
Infrastructure Solutions | Over time
Disaggregation of Revenue
Total net sales									$ 81,785	$ 105,014	$ 76,543