Revenue - Disaggregation of Revenue (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Mar. 31, 2022	Mar. 31, 2021	Mar. 31, 2022	Mar. 31, 2021
Disaggregation of Revenue [Line Items]
Revenues	$ 127,854	$ 118,716	$ 234,423	$ 225,291
Oil and gas (excludes petrochemical)
Disaggregation of Revenue [Line Items]
Revenues	53,634	50,142	96,655	90,171
Petrochemical
Disaggregation of Revenue [Line Items]
Revenues	18,853	10,196	36,081	19,361
Electric utility
Disaggregation of Revenue [Line Items]
Revenues	30,374	28,452	51,907	56,622
Traction power
Disaggregation of Revenue [Line Items]
Revenues	10,054	15,140	21,426	28,501
All others
Disaggregation of Revenue [Line Items]
Revenues	14,939	14,786	28,354	30,636
United States
Disaggregation of Revenue [Line Items]
Revenues	86,992	87,939	169,137	168,525
Canada
Disaggregation of Revenue [Line Items]
Revenues	22,053	17,734	37,178	31,825
Europe, Middle East and Africa
Disaggregation of Revenue [Line Items]
Revenues	15,551	10,937	23,381	19,193
Asia/Pacific
Disaggregation of Revenue [Line Items]
Revenues	1,646	2,009	2,590	4,725
Mexico, Central and South America
Disaggregation of Revenue [Line Items]
Revenues	$ 1,612	$ 97	$ 2,137	$ 1,023