Revenue - Disaggregation of Revenue (Details) - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2019
Disaggregation of Revenue [Line Items]
Revenue	$ 470,559	$ 518,499	$ 517,180
Oil and gas (excludes petrochemical)
Disaggregation of Revenue [Line Items]
Revenue	187,660	195,209
Petrochemical
Disaggregation of Revenue [Line Items]
Revenue	58,986	126,698
Electric utility
Disaggregation of Revenue [Line Items]
Revenue	111,244	88,818
Traction power
Disaggregation of Revenue [Line Items]
Revenue	59,106	42,373
All others
Disaggregation of Revenue [Line Items]
Revenue	53,563	65,401
United States
Disaggregation of Revenue [Line Items]
Revenue	351,422	397,983	406,609
Canada
Disaggregation of Revenue [Line Items]
Revenue	68,655	66,064	64,326
Europe, Middle East and Africa
Disaggregation of Revenue [Line Items]
Revenue	39,642	34,028
Asia/Pacific
Disaggregation of Revenue [Line Items]
Revenue	8,889	18,079	11,405
Mexico, Central and South America
Disaggregation of Revenue [Line Items]
Revenue	$ 1,951	$ 2,345	$ 2,674