Revenue - Revenue from External Customers by Geographic Areas (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017
Disaggregation of Revenue [Line Items]
Net sales	$ 138,234	$ 136,318	$ 127,073	$ 94,413	$ 131,476	$ 99,953	$ 100,922	$ 84,265	$ 496,038	$ 416,616
North America
Disaggregation of Revenue [Line Items]
Net sales	123,722	120,955	111,444	79,947					436,068
Pacific Rim
Disaggregation of Revenue [Line Items]
Net sales	9,303	10,913	11,516	10,339					42,071
Europe
Disaggregation of Revenue [Line Items]
Net sales	3,795	3,012	3,621	3,315					13,743
Other
Disaggregation of Revenue [Line Items]
Net sales	1,414	1,438	492	812					4,156
Industrial
Disaggregation of Revenue [Line Items]
Net sales	55,059	52,367	48,051	45,719					201,196
Energy
Disaggregation of Revenue [Line Items]
Net sales	46,623	48,481	52,014	38,567					185,685
Transportation
Disaggregation of Revenue [Line Items]
Net sales	$ 36,552	$ 35,470	$ 27,008	$ 10,127					$ 109,157