Revenue (Timing of Transfer) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Disaggregation of Revenue
Total net sales	$ 150,469	$ 122,454
Point in time
Disaggregation of Revenue
Total net sales	108,721	91,232
Over time
Disaggregation of Revenue
Total net sales	41,748	31,222
Rail Products and Services
Disaggregation of Revenue
Total net sales	75,694	62,170
Rail Products and Services | Point in time
Disaggregation of Revenue
Total net sales	56,492	45,871
Rail Products and Services | Over time
Disaggregation of Revenue
Total net sales	19,202	16,299
Construction Products
Disaggregation of Revenue
Total net sales	37,345	28,900
Construction Products | Point in time
Disaggregation of Revenue
Total net sales	23,095	18,926
Construction Products | Over time
Disaggregation of Revenue
Total net sales	14,250	9,974
Tubular and Energy Services
Disaggregation of Revenue
Total net sales	37,430	31,384
Tubular and Energy Services | Point in time
Disaggregation of Revenue
Total net sales	29,134	26,435
Tubular and Energy Services | Over time
Disaggregation of Revenue
Total net sales	$ 8,296	$ 4,949