CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	3 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Cash Flows From Operating Activities
Net income	$ 178,673	$ 157,646
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization expense	105,062	96,065
Deferred income taxes	46,726	40,339
Other	(616)	6,231
Net assets / liabilities from risk management activities	4,143	(2,458)
Net change in operating assets and liabilities	(161,543)	(133,139)
Net cash provided by operating activities	172,445	164,684
Cash Flows From Investing Activities
Capital expenditures	(529,186)	(416,404)
Debt and equity securities activities, net	(1,602)	(963)
Other, net	2,553	2,074
Net cash used in investing activities	(528,235)	(415,293)
Cash Flows From Financing Activities
Net decrease in short-term debt	(464,915)	(575,780)
Net proceeds from equity offering	259,005	494,734
Issuance of common stock through stock purchase and employee retirement plans	4,267	4,241
Proceeds from issuance of long-term debt	799,450	596,994
Cash dividends paid	(69,557)	(58,722)
Debt issuance costs	(7,738)	(6,432)
Net cash provided by financing activities	520,512	455,035
Net increase in cash and cash equivalents	164,722	204,426
Cash and cash equivalents at beginning of period	24,550	13,771
Cash and cash equivalents at end of period	$ 189,272	$ 218,197