Revenue - Disaggregation of Revenue (Details) - USD ($) $ in Thousands	3 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Disaggregation of Revenue [Line Items]
Revenues	$ 106,575	$ 134,150
Oil and gas
Disaggregation of Revenue [Line Items]
Revenues	40,028	59,994
Petrochemical
Disaggregation of Revenue [Line Items]
Revenues	9,165	30,426
Electric utility
Disaggregation of Revenue [Line Items]
Revenues	28,171	23,015
Traction power
Disaggregation of Revenue [Line Items]
Revenues	13,361	8,351
All others
Disaggregation of Revenue [Line Items]
Revenues	15,850	12,364
United States
Disaggregation of Revenue [Line Items]
Revenues	80,586	107,078
Canada
Disaggregation of Revenue [Line Items]
Revenues	14,091	14,454
Europe, Middle East and Africa
Disaggregation of Revenue [Line Items]
Revenues	8,256	10,166
Asia/Pacific
Disaggregation of Revenue [Line Items]
Revenues	2,716	1,686
Mexico, Central and South America
Disaggregation of Revenue [Line Items]
Revenues	$ 926	$ 766