Revenue - Disaggregation of Revenue (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Disaggregation of Revenue [Line Items]
Revenues	$ 118,062	$ 135,588	$ 403,781	$ 368,676
Oil and gas
Disaggregation of Revenue [Line Items]
Revenues	45,851	62,356	157,798	167,954
Petrochemical
Disaggregation of Revenue [Line Items]
Revenues	29,293	21,086	107,057	63,387
Electric utility
Disaggregation of Revenue [Line Items]
Revenues	16,725	26,425	63,994	66,066
Traction power
Disaggregation of Revenue [Line Items]
Revenues	9,122	7,423	31,417	18,457
All others
Disaggregation of Revenue [Line Items]
Revenues	17,071	18,298	43,515	52,812
United States
Disaggregation of Revenue [Line Items]
Revenues	89,499	99,745	318,009	292,049
Canada
Disaggregation of Revenue [Line Items]
Revenues	16,970	20,206	46,831	45,015
Europe, Middle East and Africa
Disaggregation of Revenue [Line Items]
Revenues	6,422	9,659	25,404	20,608
Asia/Pacific
Disaggregation of Revenue [Line Items]
Revenues	4,643	4,682	11,784	9,155
Mexico, Central and South America
Disaggregation of Revenue [Line Items]
Revenues	$ 528	$ 1,296	$ 1,753	$ 1,849