Condensed Consolidated Statements of Cash Flows (unaudited) - USD ($) $ in Thousands	3 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
CASH FLOWS FROM OPERATING ACTIVITIES
Net income	$ 68,303	$ 44,265
Adjustments to reconcile net income to net cash (used) provided by operating activities:
Depreciation and amortization	20,354	17,391
Deferred income tax expense	4,328	14,049
Provision for uncollectible accounts	3,459	2,442
Other, net	1,161	4,117
Net change in:
Accounts receivable and accrued utility revenues	(136,036)	(99,289)
Inventories	3,592	2,647
Deferred fuel and power costs, net of changes in unsettled derivatives	11,572	(1,000)
Accounts payable	21,655	19,358
Other current assets	(6,661)	(4,122)
Other current liabilities	1,172	4,888
Net cash (used) provided by operating activities	(7,101)	4,746
CASH FLOWS FROM INVESTING ACTIVITIES
Expenditures for property, plant and equipment	(88,686)	(69,639)
Net costs of property, plant and equipment disposals	(2,382)	(4,061)
(Increase) decrease in restricted cash	(619)	583
Net cash used by investing activities	(91,687)	(73,117)
CASH FLOWS FROM FINANCING ACTIVITIES
Payments of dividends	(15,000)	(10,000)
Issuances of long-term debt, net of issuance costs	124,374	99,490
Repayments of long-term debt	(20,000)	0
Increase (decrease) in short-term borrowings	11,500	(14,100)
Net cash provided by financing activities	100,874	75,390
Cash and cash equivalents increase	2,086	7,019
CASH AND CASH EQUIVALENTS
End of period	7,289	9,838
Beginning of period	5,203
Increase	$ 2,086	$ 7,019