Revenue - Disaggregation of Revenue (Details) - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2017
Disaggregation of Revenue [Line Items]
Revenue	$ 517,180	$ 448,716	$ 395,911
Oil and gas
Disaggregation of Revenue [Line Items]
Revenue	242,291
Petrochemical
Disaggregation of Revenue [Line Items]
Revenue	93,391
Electric utility
Disaggregation of Revenue [Line Items]
Revenue	84,993
Traction power
Disaggregation of Revenue [Line Items]
Revenue	26,781
All others
Disaggregation of Revenue [Line Items]
Revenue	69,724
United States
Disaggregation of Revenue [Line Items]
Revenue	406,609	335,743	279,352
Canada
Disaggregation of Revenue [Line Items]
Revenue	64,326	42,235	45,540
Europe, Middle East and Africa
Disaggregation of Revenue [Line Items]
Revenue	32,166
Asia/Pacific
Disaggregation of Revenue [Line Items]
Revenue	11,405
Mexico, Central and South America
Disaggregation of Revenue [Line Items]
Revenue	$ 2,674	$ 8,734	$ 19,309