CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	3 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Cash Flows From Operating Activities
Net income	$ 217,678	$ 178,673
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization expense	115,285	105,062
Deferred income taxes	64,587	46,726
Other	(2,976)	(616)
Net assets / liabilities from risk management activities	(816)	4,143
Net change in operating assets and liabilities	(236,689)	(161,543)
Net cash provided by operating activities	157,069	172,445
Cash Flows From Investing Activities
Capital expenditures	(456,809)	(529,186)
Debt and equity securities activities, net	511	(1,602)
Other, net	2,706	2,553
Net cash used in investing activities	(453,592)	(528,235)
Cash Flows From Financing Activities
Net decrease in short-term debt	0	(464,915)
Net proceeds from equity offering	216,002	259,005
Issuance of common stock through stock purchase and employee retirement plans	4,007	4,267
Proceeds from issuance of long-term debt	597,390	799,450
Cash dividends paid	(79,023)	(69,557)
Debt issuance costs	(5,062)	(7,738)
Net cash provided by financing activities	733,314	520,512
Net increase in cash and cash equivalents	436,791	164,722
Cash and cash equivalents at beginning of period	20,808	24,550
Cash and cash equivalents at end of period	$ 457,599	$ 189,272