Revenue (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
Rail Products and Services
Disaggregation of Revenue
Total net sales	91,884	69,347	154,054	125,827
Rail Products and Services | Rail Products
Disaggregation of Revenue
Total net sales	54,332	44,399	90,366	78,764
Rail Products and Services | Rail Technologies
Disaggregation of Revenue
Total net sales	37,552	24,948	63,688	47,063
Construction Products
Disaggregation of Revenue
Total net sales	42,207	45,465	71,107	82,787
Construction Products | Piling and Fabricated Bridge
Disaggregation of Revenue
Total net sales	25,846	29,607	44,707	58,830
Construction Products | Precast Concrete Products
Disaggregation of Revenue
Total net sales	16,361	15,858	26,400	23,957
Tubular and Energy Services
Disaggregation of Revenue
Total net sales	38,799	30,048	70,183	54,948
Tubular and Energy Services | Test Inspection and Threading
Disaggregation of Revenue
Total net sales	15,008	13,050	29,221	23,932
Tubular and Energy Services | Protective Coating and Measurements Solutions
Disaggregation of Revenue
Total net sales	$ 23,791	$ 16,998	$ 40,962	$ 31,016