Revenue - Disaggregation of Revenue (Details) - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2018
Disaggregation of Revenue [Line Items]
Revenue	$ 518,499	$ 517,180	$ 448,716
Oil and gas
Disaggregation of Revenue [Line Items]
Revenue	195,209	242,291
Petrochemical
Disaggregation of Revenue [Line Items]
Revenue	126,698	93,391
Electric utility
Disaggregation of Revenue [Line Items]
Revenue	88,818	84,993
Traction power
Disaggregation of Revenue [Line Items]
Revenue	42,373	26,781
All others
Disaggregation of Revenue [Line Items]
Revenue	65,401	69,724
United States
Disaggregation of Revenue [Line Items]
Revenue	397,983	406,609	335,743
Canada
Disaggregation of Revenue [Line Items]
Revenue	66,064	64,326	42,235
Europe, Middle East and Africa
Disaggregation of Revenue [Line Items]
Revenue	34,028	32,166
Asia/Pacific
Disaggregation of Revenue [Line Items]
Revenue	18,079	11,405
Mexico, Central and South America
Disaggregation of Revenue [Line Items]
Revenue	$ 2,345	$ 2,674	$ 8,734