Revenue - Disaggregation of Revenue (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Disaggregation of Revenue [Line Items]
Revenues	$ 115,813	$ 118,062	$ 341,105	$ 403,781
Oil and gas
Disaggregation of Revenue [Line Items]
Revenues	49,272	45,851	139,443	157,798
Petrochemical
Disaggregation of Revenue [Line Items]
Revenues	15,365	29,293	34,725	107,057
Electric utility
Disaggregation of Revenue [Line Items]
Revenues	26,175	16,725	82,797	63,994
Traction power
Disaggregation of Revenue [Line Items]
Revenues	13,821	9,122	42,322	31,417
All others
Disaggregation of Revenue [Line Items]
Revenues	11,180	17,071	41,818	43,515
United States
Disaggregation of Revenue [Line Items]
Revenues	88,412	89,499	256,937	318,009
Canada
Disaggregation of Revenue [Line Items]
Revenues	16,529	16,970	48,354	46,831
Europe, Middle East and Africa
Disaggregation of Revenue [Line Items]
Revenues	8,926	6,422	28,120	25,404
Asia/Pacific
Disaggregation of Revenue [Line Items]
Revenues	1,651	4,643	6,376	11,784
Mexico, Central and South America
Disaggregation of Revenue [Line Items]
Revenues	$ 295	$ 528	$ 1,318	$ 1,753