REVENUE - TIMING OF REVENUE RECOGNITION - BALANCE SHEET (Details) - USD ($) $ in Thousands	Mar. 31, 2021	Sep. 30, 2020
Customer accounts receivable
Billed	$ 237,229	$ 134,173
Unbilled revenues	41,941	9,226
Customers' credit balances and deposits	(20,763)	$ (25,934)
Customers accounts receivables & Customers' credit balances and deposits	258,407
Operating Segments | Natural Gas Distribution
Customer accounts receivable
Billed	119,845
Unbilled revenues	39,652
Customers' credit balances and deposits	(20,763)
Customers accounts receivables & Customers' credit balances and deposits	138,734
Operating Segments | Clean Energy Ventures
Customer accounts receivable
Billed	4,794
Unbilled revenues	2,289
Customers' credit balances and deposits	0
Customers accounts receivables & Customers' credit balances and deposits	7,083
Operating Segments | Energy Services
Customer accounts receivable
Billed	107,353
Unbilled revenues	0
Customers' credit balances and deposits	0
Customers accounts receivables & Customers' credit balances and deposits	107,353
Operating Segments | Storage and Transportation
Customer accounts receivable
Billed	3,437
Unbilled revenues	0
Customers' credit balances and deposits	0
Customers accounts receivables & Customers' credit balances and deposits	3,437
Home Services and Other
Customer accounts receivable
Billed	1,800
Unbilled revenues	0
Customers' credit balances and deposits	0
Customers accounts receivables & Customers' credit balances and deposits	$ 1,800