CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2016
CASH FLOWS FROM OPERATING ACTIVITIES
Net income	$ 603,064	$ 396,421	$ 350,104
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	361,083	319,633	293,096
Deferred income taxes	158,271	227,183	193,556
One-time income tax benefit	(158,782)	0	0
Gain on sale of discontinued operations	0	(12,931)	0
Gain on Discontinuation of Cash Flow Hedge Due to Forecasted Transaction Probable of Not Occurring	0	(10,579)	0
Stock-based compensation	12,863	14,064	14,760
Debt financing costs	7,865	6,469	5,667
Other	5,437	97	1,019
Changes in assets and liabilities:
(Increase) decrease in accounts receivable	(29,208)	(58,696)	(4,847)
(Increase) decrease in gas stored underground	18,921	(35,126)	20,577
(Increase) decrease in other current assets	60,424	9,991	(18,739)
(Increase) decrease in deferred charges and other assets	(10,049)	102,254	(24,860)
Increase (decrease) in accounts payable and accrued liabilities	(11,857)	53,017	(5,195)
Increase (decrease) in other current liabilities	74,707	(78,651)	(44,482)
Increase (decrease) in deferred credits and other liabilities	31,923	(66,056)	14,334
Net cash provided by operating activities	1,124,662	867,090	794,990
CASH FLOWS USED IN INVESTING ACTIVITIES
Capital expenditures	(1,467,591)	(1,137,089)	(1,086,950)
Acquisition	0	(86,128)	0
Proceeds from the sale of discontinued operations	3,000	140,253	0
Purchases of available-for-sale securities	(46,401)	(53,597)	(32,551)
Proceeds from sale of available-for-sale securities	22,360	31,792	27,019
Maturities of available-for-sale securities	15,716	9,332	6,290
Use tax refund	790	29,790	0
Other, net	8,560	9,341	6,460
Net cash used in investing activities	(1,463,566)	(1,056,306)	(1,079,732)
CASH FLOWS FROM FINANCING ACTIVITIES
Net increase (decrease) in short-term debt	128,035	(382,066)	371,884
Proceeds from issuance of long-term debt, net of premium/discount	0	884,911	0
Net proceeds from equity offering	395,092	98,755	98,574
Issuance of common stock through stock purchase and employee retirement plans	19,563	26,523	34,278
Settlement of interest rate agreements	0	(36,996)	0
Interest rate agreements cash collateral	0	25,670	(25,670)
Repayment of long-term debt	0	(250,000)	0
Cash dividends paid	(214,906)	(191,931)	(175,126)
Debt issuance costs	0	(6,775)	(317)
Other	(1,518)	0	0
Net cash provided by financing activities	326,266	168,091	303,623
Net increase (decrease) in cash and cash equivalents	(12,638)	(21,125)	18,881
Cash and cash equivalents at beginning of year	26,409	47,534	28,653
Cash and cash equivalents at end of year	13,771	26,409	47,534
CASH PAID (RECEIVED) DURING THE PERIOD FOR:
Interest	169,987	156,668	154,748
Income taxes	$ 6,102	$ 5,264	$ 7,794