Revenue (Timing of Transfer) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Disaggregation of Revenue
Total net sales	$ 200,933	$ 172,890	$ 351,402	$ 295,344
Point in time
Disaggregation of Revenue
Total net sales	152,338	132,414	261,059	223,646
Over time
Disaggregation of Revenue
Total net sales	48,595	40,476	90,343	71,698
Rail Products and Services
Disaggregation of Revenue
Total net sales	101,401	91,884	177,095	154,054
Rail Products and Services | Point in time
Disaggregation of Revenue
Total net sales	80,701	69,295	137,193	115,166
Rail Products and Services | Over time
Disaggregation of Revenue
Total net sales	20,700	22,589	39,902	38,888
Construction Products
Disaggregation of Revenue
Total net sales	55,406	42,207	92,751	71,107
Construction Products | Point in time
Disaggregation of Revenue
Total net sales	38,095	28,196	61,190	47,122
Construction Products | Over time
Disaggregation of Revenue
Total net sales	17,311	14,011	31,561	23,985
Tubular and Energy Services
Disaggregation of Revenue
Total net sales	44,126	38,799	81,556	70,183
Tubular and Energy Services | Point in time
Disaggregation of Revenue
Total net sales	33,542	34,923	62,676	61,358
Tubular and Energy Services | Over time
Disaggregation of Revenue
Total net sales	$ 10,584	$ 3,876	$ 18,880	$ 8,825