CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS (Unaudited) - USD ($)	6 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
CASH FLOWS FROM OPERATING ACTIVITIES
Net income	$ 230,854,000	$ 149,598,000
Adjustments to reconcile net income to cash flows from operating activities
Unrealized gain on derivative instruments	(8,235,000)	(45,539,000)
Depreciation and amortization	54,210,000	52,153,000
Amortization of acquired wholesale energy contracts	3,401,000	3,953,000
Allowance for equity used during construction	(10,603,000)	(8,053,000)
Allowance for doubtful accounts	10,607,000	951,000
Non cash lease expense	1,957,000	1,856,000
Deferred income taxes	20,909,000	34,975,000
Manufactured gas plant remediation costs	(6,284,000)	(5,291,000)
Equity in earnings, net of distributions received from equity investees	(3,543,000)	(2,760,000)
Cost of removal - asset retirement obligations	(512,000)	(122,000)
Contributions to postemployment benefit plans	(2,018,000)	(5,742,000)
Taxes related to stock-based compensation	(145,000)	803,000
Changes in:
Components of working capital	6,846,000	3,526,000
Other noncurrent assets	18,854,000	(1,258,000)
Other noncurrent liabilities	39,993,000	95,000
Cash flows from operating activities	356,291,000	179,145,000
Expenditures for:
Cost of removal	(23,989,000)	(17,487,000)
Acquisition of assets, net of cash acquired of $5.1 million	0	(523,647,000)
Distribution from equity investees in excess of equity in earnings	871,000	1,132,000
Investments in equity investees	(482,000)	(1,266,000)
Cash flows used in investing activities	(245,498,000)	(751,130,000)
CASH FLOWS (USED IN) FROM FINANCING ACTIVITIES
Payments of long-term debt	(11,001,000)	(9,764,000)
Proceeds from term loan	0	350,000,000
Payments of term loan	0	(212,900,000)
(Payments of) proceeds from short-term debt, net	(116,850,000)	304,023,000
Proceeds from sale leaseback transaction - solar	12,124,000	0
Proceeds from sale leaseback transaction	0	4,000,000
Payments of common stock dividends	(60,894,000)	(56,821,000)
Proceeds from issuance of common stock - public equity offering	0	212,900,000
Cash settlement of equity forward agreement	(388,000)	0
Proceeds from issuance of common stock - DRP	7,540,000	8,767,000
Tax withholding payments related to net settled stock compensation	(1,772,000)	(3,893,000)
Cash flows (used in) from financing activities	(171,241,000)	596,312,000
Change in cash, cash equivalents and restricted cash	(60,448,000)	24,327,000
Cash, cash equivalents and restricted cash at beginning of period	119,423,000	4,063,000
Cash, cash equivalents and restricted cash at end of period	58,975,000	28,390,000
CHANGES IN COMPONENTS OF WORKING CAPITAL
Receivables	(136,295,000)	(87,532,000)
Inventories	94,233,000	90,484,000
Recovery of natural gas costs	(20,279,000)	(21,891,000)
Natural gas purchases payable	33,191,000	(10,933,000)
Natural gas purchases payable - related parties	62,000	11,000
Accounts payable and other	(19,621,000)	(27,345,000)
Prepaid expenses	(8,170,000)	(602,000)
Prepaid and accrued taxes	59,614,000	22,258,000
Restricted broker margin accounts	7,644,000	39,193,000
Customers' credit balances and deposits	(5,171,000)	(7,788,000)
Other current assets	1,638,000	7,671,000
Total	6,846,000	3,526,000
Cash paid for:
Interest (net of amounts capitalized)	40,465,000	32,872,000
Income taxes	3,733,000	1,193,000
Accrued capital expenditures	22,840,000	17,930,000
Utility Plant
Expenditures for:
Payments to acquire PP&E	(152,496,000)	(132,352,000)
Solar Equipment
Expenditures for:
Payments to acquire PP&E	(40,884,000)	(69,786,000)
Storage and Transportation and other
Expenditures for:
Payments to acquire PP&E	$ (28,518,000)	$ (7,724,000)