Revenue (Timing of Transfer) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Disaggregation of Revenue
Total net sales	$ 172,890	$ 144,860	$ 295,344	$ 263,562
Point in time
Disaggregation of Revenue
Total net sales	132,414	111,976	223,646	203,105
Over time
Disaggregation of Revenue
Total net sales	40,476	32,884	71,698	60,457
Rail Products and Services
Disaggregation of Revenue
Total net sales	91,884	69,347	154,054	125,827
Rail Products and Services | Point in time
Disaggregation of Revenue
Total net sales	69,295	57,098	115,166	102,664
Rail Products and Services | Over time
Disaggregation of Revenue
Total net sales	22,589	12,249	38,888	23,163
Construction Products
Disaggregation of Revenue
Total net sales	42,207	45,465	71,107	82,787
Construction Products | Point in time
Disaggregation of Revenue
Total net sales	28,196	28,766	47,122	53,390
Construction Products | Over time
Disaggregation of Revenue
Total net sales	14,011	16,699	23,985	29,397
Tubular and Energy Services
Disaggregation of Revenue
Total net sales	38,799	30,048	70,183	54,948
Tubular and Energy Services | Point in time
Disaggregation of Revenue
Total net sales	34,923	26,112	61,358	47,051
Tubular and Energy Services | Over time
Disaggregation of Revenue
Total net sales	$ 3,876	$ 3,936	$ 8,825	$ 7,897