Revenue - Disaggregation of Revenue (Details) - USD ($) $ in Thousands	3 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Disaggregation of Revenue [Line Items]
Revenues	$ 134,150	$ 109,351
Oil and gas
Disaggregation of Revenue [Line Items]
Revenues	59,994	49,576
Petrochemical
Disaggregation of Revenue [Line Items]
Revenues	30,426	19,778
Electric utility
Disaggregation of Revenue [Line Items]
Revenues	23,015	19,258
Traction power
Disaggregation of Revenue [Line Items]
Revenues	8,351	5,009
All others
Disaggregation of Revenue [Line Items]
Revenues	12,364	15,730
United States
Disaggregation of Revenue [Line Items]
Revenues	107,078	89,898
Canada
Disaggregation of Revenue [Line Items]
Revenues	14,454	9,715
Europe, Middle East and Africa
Disaggregation of Revenue [Line Items]
Revenues	10,166	5,441
Asia/Pacific
Disaggregation of Revenue [Line Items]
Revenues	1,686	3,744
Mexico, Central and South America
Disaggregation of Revenue [Line Items]
Revenues	$ 766	$ 553