Revenue (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
Rail Products and Services
Disaggregation of Revenue
Total net sales	84,517	62,095	238,571	187,922
Rail Products and Services | Rail Products
Disaggregation of Revenue
Total net sales	49,234	36,297	139,600	115,061
Rail Products and Services | Rail Technologies
Disaggregation of Revenue
Total net sales	35,283	25,798	98,971	72,861
Construction Products
Disaggregation of Revenue
Total net sales	41,534	39,118	112,641	121,905
Construction Products | Piling and Fabricated Bridge
Disaggregation of Revenue
Total net sales	26,798	24,186	71,505	83,016
Construction Products | Precast Concrete Products
Disaggregation of Revenue
Total net sales	14,736	14,932	41,136	38,889
Tubular and Energy Services
Disaggregation of Revenue
Total net sales	41,043	30,279	111,226	85,227
Tubular and Energy Services | Test Inspection and Threading
Disaggregation of Revenue
Total net sales	15,296	13,729	44,517	37,661
Tubular and Energy Services | Protective Coating and Measurements Solutions
Disaggregation of Revenue
Total net sales	$ 25,747	$ 16,550	$ 66,709	$ 47,566