REVENUE - TIMING OF REVENUE RECOGNITION - BALANCE SHEET (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Sep. 30, 2020
Customer accounts receivable
Billed	$ 197,641	$ 134,173
Unbilled revenues	53,794	9,226
Customers' credit balances and deposits	(32,948)	$ (25,934)
Customers accounts receivables & Customers' credit balances and deposits	218,487
Operating Segments | Natural Gas Distribution
Customer accounts receivable
Billed	79,146
Unbilled revenues	51,720
Customers' credit balances and deposits	(32,948)
Customers accounts receivables & Customers' credit balances and deposits	97,918
Operating Segments | Clean Energy Ventures
Customer accounts receivable
Billed	4,436
Unbilled revenues	2,074
Customers' credit balances and deposits	0
Customers accounts receivables & Customers' credit balances and deposits	6,510
Operating Segments | Energy Services
Customer accounts receivable
Billed	108,544
Unbilled revenues	0
Customers' credit balances and deposits	0
Customers accounts receivables & Customers' credit balances and deposits	108,544
Operating Segments | Storage and Transportation
Customer accounts receivable
Billed	3,559
Unbilled revenues	0
Customers' credit balances and deposits	0
Customers accounts receivables & Customers' credit balances and deposits	3,559
Home Services and Other
Customer accounts receivable
Billed	1,956
Unbilled revenues	0
Customers' credit balances and deposits	0
Customers accounts receivables & Customers' credit balances and deposits	$ 1,956