REVENUE - Disaggregation of Revenue (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Disaggregation of Revenue [Line Items]
Revenues	$ 135,588	$ 122,130	$ 368,676	$ 313,819
Oil and gas
Disaggregation of Revenue [Line Items]
Revenues	62,356		167,954
Petrochemical
Disaggregation of Revenue [Line Items]
Revenues	21,086		63,387
Electric utility
Disaggregation of Revenue [Line Items]
Revenues	26,425		66,066
Traction power
Disaggregation of Revenue [Line Items]
Revenues	7,423		18,457
All others
Disaggregation of Revenue [Line Items]
Revenues	18,298		52,812
United States
Disaggregation of Revenue [Line Items]
Revenues	99,745		292,049
Canada
Disaggregation of Revenue [Line Items]
Revenues	20,206		45,015
Europe, Middle East and Africa
Disaggregation of Revenue [Line Items]
Revenues	9,659		20,608
Asia/Pacific
Disaggregation of Revenue [Line Items]
Revenues	4,682		9,155
Mexico, Central and South America
Disaggregation of Revenue [Line Items]
Revenues	$ 1,296		$ 1,849