Revenue (Timing of Transfer) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Disaggregation of Revenue
Total net sales	$ 122,454	$ 118,702
Point in time
Disaggregation of Revenue
Total net sales	91,232	91,129
Over time
Disaggregation of Revenue
Total net sales	31,222	27,573
Rail Products and Services
Disaggregation of Revenue
Total net sales	62,170	56,480
Rail Products and Services | Point in time
Disaggregation of Revenue
Total net sales	45,871	45,566
Rail Products and Services | Over time
Disaggregation of Revenue
Total net sales	16,299	10,914
Construction Products
Disaggregation of Revenue
Total net sales	28,900	37,322
Construction Products | Point in time
Disaggregation of Revenue
Total net sales	18,926	24,624
Construction Products | Over time
Disaggregation of Revenue
Total net sales	9,974	12,698
Tubular and Energy Services
Disaggregation of Revenue
Total net sales	31,384	24,900
Tubular and Energy Services | Point in time
Disaggregation of Revenue
Total net sales	26,435	20,939
Tubular and Energy Services | Over time
Disaggregation of Revenue
Total net sales	$ 4,949	$ 3,961