Revenue - Revenue from External Customers by Geographic Areas (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Disaggregation of Revenue [Line Items]
Total	$ 138,512	$ 136,318	$ 392,983	$ 357,804
North America
Disaggregation of Revenue [Line Items]
Total	125,971	120,955	343,593	312,346
Pacific Rim
Disaggregation of Revenue [Line Items]
Total	6,744	10,913	30,173	32,768
Europe
Disaggregation of Revenue [Line Items]
Total	4,329	3,012	12,712	9,948
Other
Disaggregation of Revenue [Line Items]
Total	1,468	1,438	6,505	2,742
Energy
Disaggregation of Revenue [Line Items]
Total	64,331	48,481	162,224	139,062
Industrial
Disaggregation of Revenue [Line Items]
Total	37,020	52,367	142,267	146,137
Transportation
Disaggregation of Revenue [Line Items]
Total	$ 37,161	$ 35,470	$ 88,492	$ 72,605