Revenue (Timing of Transfer) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Disaggregation of Revenue
Total net sales	$ 167,094	$ 131,492	$ 462,438	$ 395,054
Point in time
Disaggregation of Revenue
Total net sales	122,359	99,949	346,005	303,054
Over time
Disaggregation of Revenue
Total net sales	44,735	31,543	116,433	92,000
Rail Products and Services
Disaggregation of Revenue
Total net sales	84,517	62,095	238,571	187,922
Rail Products and Services | Point in time
Disaggregation of Revenue
Total net sales	61,426	51,043	176,592	153,707
Rail Products and Services | Over time
Disaggregation of Revenue
Total net sales	23,091	11,052	61,979	34,215
Construction Products
Disaggregation of Revenue
Total net sales	41,534	39,118	112,641	121,905
Construction Products | Point in time
Disaggregation of Revenue
Total net sales	27,459	22,768	74,581	76,158
Construction Products | Over time
Disaggregation of Revenue
Total net sales	14,075	16,350	38,060	45,747
Tubular and Energy Services
Disaggregation of Revenue
Total net sales	41,043	30,279	111,226	85,227
Tubular and Energy Services | Point in time
Disaggregation of Revenue
Total net sales	33,474	26,138	94,832	73,189
Tubular and Energy Services | Over time
Disaggregation of Revenue
Total net sales	$ 7,569	$ 4,141	$ 16,394	$ 12,038