Revenue - Timing of Transfer (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
Point in time
Disaggregation of Revenue
Total net sales	111,348	106,017	198,056	195,147
Over time
Disaggregation of Revenue
Total net sales	43,174	35,546	72,546	68,323
Rail Technologies and Services
Disaggregation of Revenue
Total net sales	88,782	74,939	155,014	145,143
Rail Technologies and Services | Point in time
Disaggregation of Revenue
Total net sales	71,711	61,275	123,755	116,163
Rail Technologies and Services | Over time
Disaggregation of Revenue
Total net sales	17,071	13,664	31,259	28,980
Infrastructure Solutions
Disaggregation of Revenue
Total net sales	65,740	66,624	115,588	118,327
Infrastructure Solutions | Point in time
Disaggregation of Revenue
Total net sales	39,637	44,742	74,301	78,984
Infrastructure Solutions | Over time
Disaggregation of Revenue
Total net sales	$ 26,103	$ 21,882	$ 41,287	$ 39,343