Revenue - Disaggregation of Revenue (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Mar. 31, 2020	Mar. 31, 2019	Mar. 31, 2020	Mar. 31, 2019
Disaggregation of Revenue [Line Items]
Revenues	$ 151,570	$ 123,737	$ 285,720	$ 233,088
Oil and gas
Disaggregation of Revenue [Line Items]
Revenues	51,954	56,022	111,948	105,598
Petrochemical
Disaggregation of Revenue [Line Items]
Revenues	47,337	22,523	77,763	42,301
Electric utility
Disaggregation of Revenue [Line Items]
Revenues	24,255	20,383	47,270	39,641
Traction power
Disaggregation of Revenue [Line Items]
Revenues	13,944	6,025	22,295	11,034
All others
Disaggregation of Revenue [Line Items]
Revenues	14,080	18,784	26,444	34,514
United States
Disaggregation of Revenue [Line Items]
Revenues	121,432	102,406	228,510	192,304
Canada
Disaggregation of Revenue [Line Items]
Revenues	15,407	15,094	29,861	24,809
Europe, Middle East and Africa
Disaggregation of Revenue [Line Items]
Revenues	8,816	5,508	18,982	10,949
Asia/Pacific
Disaggregation of Revenue [Line Items]
Revenues	5,456	729	7,142	4,473
Mexico, Central and South America
Disaggregation of Revenue [Line Items]
Revenues	$ 459	$ 0	$ 1,225	$ 553