REVENUE - Disaggregation of Revenue (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Mar. 31, 2019	Mar. 31, 2018
Disaggregation of Revenue [Line Items]
Revenues	$ 123,737	$ 101,505	$ 233,088	$ 191,689
Oil and gas
Disaggregation of Revenue [Line Items]
Revenues	56,022		105,598
Petrochemical
Disaggregation of Revenue [Line Items]
Revenues	22,523		42,301
Electric utility
Disaggregation of Revenue [Line Items]
Revenues	20,383		39,641
Traction power
Disaggregation of Revenue [Line Items]
Revenues	6,025		11,034
All others
Disaggregation of Revenue [Line Items]
Revenues	18,784		34,514
United States
Disaggregation of Revenue [Line Items]
Revenues	102,406		192,304
Canada
Disaggregation of Revenue [Line Items]
Revenues	15,094		24,809
Europe, Middle East and Africa
Disaggregation of Revenue [Line Items]
Revenues	5,508		10,949
Asia/Pacific
Disaggregation of Revenue [Line Items]
Revenues	729		4,473
Mexico, Central and South America
Disaggregation of Revenue [Line Items]
Revenues	$ 0		$ 553