Consolidated Statements Of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2018
Operating Activities
Net Income (Loss) Available for Common Stock	$ (123,772)	$ 304,290	$ 391,521
Adjustments to Reconcile Net Income to Net Cash Provided by Operating Activities:
Impairment of Oil and Gas Producing Properties	449,438	0	0
Depreciation, Depletion and Amortization	306,158	275,660	240,961
Deferred Income Taxes	54,313	122,265	(18,153)
Stock-Based Compensation	14,931	21,186	15,762
Other	6,527	8,608	16,133
Change in:
Receivables and Unbilled Revenue	(2,578)	6,379	(30,882)
Gas Stored Underground and Materials, Supplies and Emission Allowances	(6,625)	(3,713)	(4,021)
Unrecovered Purchased Gas Costs	2,246	1,958	419
Other Current Assets	49,367	(29,030)	(16,519)
Accounts Payable	(4,657)	(24,770)	17,962
Amounts Payable to Customers	6,771	623	3,394
Customer Advances	2,275	(565)	(2,092)
Customer Security Deposits	989	(9,493)	5,331
Other Accruals and Current Liabilities	5,001	10,992	3,865
Other Assets	(24,203)	5,115	(9,556)
Other Liabilities	4,628	4,978	1,178
Net Cash Provided by Operating Activities	740,809	694,483	615,303
Investing Activities
Capital Expenditures	(716,153)	(788,938)	(584,004)
Acquisition of Upstream Assets and Midstream Gathering Assets	(506,258)	0	0
Net Proceeds from Sale of Oil and Gas Producing Properties	0	0	55,506
Other	(1,205)	(10,237)	(389)
Net Cash Used in Investing Activities	(1,223,616)	(799,175)	(528,887)
Financing Activities
Change in Notes Payable to Banks and Commercial Paper	(25,200)	55,200	0
Net Proceeds from Issuance of Long-Term Debt	493,007	0	295,020
Reduction of Long-Term Debt	0	0	(566,512)
Net Repurchases of Common Stock		(8,877)
Net Proceeds from Issuance of Common Stock	161,603		4,110
Dividends Paid on Common Stock	(153,322)	(147,418)	(143,258)
Net Cash Provided by (Used in) Financing Activities	476,088	(101,095)	(410,640)
Net Decrease in Cash, Cash Equivalents, and Restricted Cash	(6,719)	(205,787)	(324,224)
Cash, Cash Equivalents and Restricted Cash At Beginning of Year	27,260	233,047	557,271
Cash, Cash Equivalents and Restricted Cash At End of Year	20,541	27,260	233,047
Supplemental Disclosure of Cash Flow Information
Cash Paid for Interest	103,479	102,920	126,079
Cash Refunded for Income Taxes	(82,876)	(17,342)
Cash Paid for Income Taxes			31,771
Supplemental Disclosure of Cash Flow Information, Non-Cash Investing Activities
Non-Cash Capital Expenditures	$ 87,328	$ 81,121	$ 88,813