Revenue - Disaggregation of Revenue (Details) - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2021
Disaggregation of Revenue [Line Items]
Revenue	$ 699,308	$ 532,582	$ 470,559
Oil and gas (excludes petrochemical)
Disaggregation of Revenue [Line Items]
Revenue	273,117	215,235	187,660
Petrochemical
Disaggregation of Revenue [Line Items]
Revenue	94,188	66,538	58,986
Electric utility
Disaggregation of Revenue [Line Items]
Revenue	158,400	122,361	111,244
Traction power
Disaggregation of Revenue [Line Items]
Revenue	28,112	44,930	59,106
Commercial and other industrial
Disaggregation of Revenue [Line Items]
Revenue	103,966	56,448	27,065
All others
Disaggregation of Revenue [Line Items]
Revenue	41,525	27,070	26,498
United States
Disaggregation of Revenue [Line Items]
Revenue	557,934	404,973	351,422
Canada
Disaggregation of Revenue [Line Items]
Revenue	84,090	81,218	68,655
Middle East and Africa
Disaggregation of Revenue [Line Items]
Revenue	14,998	20,712	26,615
Asia/Pacific
Disaggregation of Revenue [Line Items]
Revenue	6,188	4,885	8,889
Europe
Disaggregation of Revenue [Line Items]
Revenue	26,699	17,699	13,027
Mexico, Central and South America
Disaggregation of Revenue [Line Items]
Revenue	$ 9,399	$ 3,095	$ 1,951