CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS (UNAUDITED) - USD ($) $ in Thousands	3 Months Ended
	Dec. 31, 2016	Dec. 31, 2015
Cash Flows From Operating Activities
Net income	$ 125,032	$ 102,861
Adjustments to reconcile net income to net cash provided by operating activities:
Charged to depreciation and amortization	77,143	71,239
Deferred income taxes	67,241	59,299
Discontinued cash flow hedging for natural gas marketing commodity contracts	(10,579)	0
Other	4,842	3,471
Net Assets Liabilities From Risk Management Activities	3,969	(7,495)
Net change in operating assets and liabilities	(150,685)	(159,234)
Net cash provided by operating activities	116,963	70,141
Cash Flows From Investing Activities
Capital expenditures	(297,962)	(290,412)
Acquisition	(85,714)	0
Available-for-sale securities activities, net	(10,263)	(2,263)
Other, net	1,802	2,382
Net cash used in investing activities	(392,137)	(290,293)
Cash Flows From Financing Activities
Net increase in short-term debt	110,936	305,309
Net proceeds from equity offering	49,400	0
Issuance of common stock through stock purchase and employee retirement plans	8,998	8,729
Proceeds from issuance of long-term debt, net of discount	125,000	0
Interest rate agreements cash collateral	25,670	0
Cash dividends paid	(47,740)	(43,636)
Net cash provided by (used in) financing activities	272,264	270,402
Net increase (decrease) in cash and cash equivalents	(2,910)	50,250
Cash and cash equivalents at beginning of period	47,534	28,653
Cash and cash equivalents at end of period	$ 44,624	$ 78,903