Revenue - Disaggregation of Revenue (Details) - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2022	Sep. 30, 2021	Sep. 30, 2020
Disaggregation of Revenue [Line Items]
Revenue	$ 532,582	$ 470,559	$ 518,499
Oil and gas (excludes petrochemical)
Disaggregation of Revenue [Line Items]
Revenue	215,235	187,660
Petrochemical
Disaggregation of Revenue [Line Items]
Revenue	66,538	58,986
Electric utility
Disaggregation of Revenue [Line Items]
Revenue	122,361	111,244
Traction power
Disaggregation of Revenue [Line Items]
Revenue	44,930	59,106
Commercial and other industrial
Disaggregation of Revenue [Line Items]
Revenue	56,448	27,065
All others
Disaggregation of Revenue [Line Items]
Revenue	27,070	26,498
United States
Disaggregation of Revenue [Line Items]
Revenue	404,973	351,422	397,983
Canada
Disaggregation of Revenue [Line Items]
Revenue	81,218	68,655	66,064
Europe, Middle East and Africa
Disaggregation of Revenue [Line Items]
Revenue	38,411	39,642
Asia/Pacific
Disaggregation of Revenue [Line Items]
Revenue	4,885	8,889	18,079
Mexico, Central and South America
Disaggregation of Revenue [Line Items]
Revenue	$ 3,095	$ 1,951	$ 2,345