Revenue - Revenue from External Customers by Geographic Areas (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 [Line Items]
Total	$ 138,684	$ 127,073	$ 254,471	$ 221,486
North America
Disaggregation of Revenue [Line Items]
Total	119,943	111,444	217,622	191,391
Pacific Rim
Disaggregation of Revenue [Line Items]
Total	10,804	11,516	23,429	21,855
Europe
Disaggregation of Revenue [Line Items]
Total	5,006	3,621	8,383	6,936
Other
Disaggregation of Revenue [Line Items]
Total	2,931	492	5,037	1,304
Industrial
Disaggregation of Revenue [Line Items]
Total	54,660	48,051	105,247	93,770
Energy
Disaggregation of Revenue [Line Items]
Total	52,245	52,014	97,893	90,581
Transportation
Disaggregation of Revenue [Line Items]
Total	$ 31,779	$ 27,008	$ 51,331	$ 37,135