Consolidated Statements Of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2017
Operating Activities
Net Income Available for Common Stock	$ 304,290	$ 391,521	$ 283,482
Adjustments to Reconcile Net Income to Net Cash Provided by Operating Activities:
Depreciation, Depletion and Amortization	275,660	240,961	224,195
Deferred Income Taxes	122,265	(18,153)	117,975
Stock-Based Compensation	21,186	15,762	12,262
Other	8,608	16,133	16,476
Change in:
Receivables and Unbilled Revenue	6,379	(30,882)	(3,380)
Gas Stored Underground and Materials and Supplies	(3,713)	(4,021)	(1,417)
Unrecovered Purchased Gas Costs	1,958	419	(2,183)
Other Current Assets	(29,030)	(16,519)	7,849
Accounts Payable	(24,770)	17,962	17,192
Amounts Payable to Customers	623	3,394	(19,537)
Customer Advances	(565)	(2,092)	939
Customer Security Deposits	(9,493)	5,331	4,353
Other Accruals and Current Liabilities	10,992	3,865	27,004
Other Assets	5,115	(9,556)	(2,885)
Other Liabilities	4,978	1,178	2,183
Net Cash Provided by Operating Activities	694,483	615,303	684,508
Investing Activities
Capital Expenditures	(788,938)	(584,004)	(450,335)
Net Proceeds from Sale of Oil and Gas Producing Properties	0	55,506	26,554
Other	(10,237)	(389)	1,216
Net Cash Used in Investing Activities	(799,175)	(528,887)	(422,565)
Financing Activities
Change in Notes Payable to Banks and Commercial Paper	55,200	0	0
Net Proceeds from Issuance of Long-Term Debt	0	295,020	295,151
Reduction of Long-Term Debt	0	(566,512)	0
Net Repurchases of Common Stock	(8,877)
Net Proceeds from Issuance of Common Stock		4,110	7,784
Dividends Paid on Common Stock	(147,418)	(143,258)	(139,063)
Net Cash Provided by (Used in) Financing Activities	(101,095)	(410,640)	163,872
Net Increase (Decrease) in Cash, Cash Equivalents, and Restricted Cash	(205,787)	(324,224)	425,815
Cash, Cash Equivalents and Restricted Cash At Beginning of Year	233,047	557,271	131,456
Cash, Cash Equivalents and Restricted Cash At End of Year	27,260	233,047	557,271
Supplemental Disclosure of Cash Flow Information
Cash Paid for Interest	102,920	126,079	116,894
Cash Refunded for Income Taxes	(17,342)
Cash Paid for Income Taxes		31,771	34,826
Supplemental Disclosure of Cash Flow Information, Non-Cash Investing Activities
Non-Cash Capital Expenditures	$ 81,121	$ 88,813	$ 72,216