CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS (Unaudited) - USD ($) $ in Thousands	9 Months Ended
	Jun. 30, 2018	Jun. 30, 2017
CASH FLOWS FROM OPERATING ACTIVITIES
Net (loss) income	$ 249,691	$ 168,588
Adjustments to reconcile net income to cash flows from operating activities
Unrealized loss (gain) on derivative instruments	25,904	(42,534)
Gain on sale of available for sale securities	(5,332)	(7,287)
Gain on sale of businesses	(4,687)	0
Depreciation and amortization	64,634	60,348
Amortization of acquired wholesale energy contracts	17,813	0
Allowance for equity used during construction	(3,730)	(2,738)
Allowance for doubtful accounts	1,672	916
Deferred income taxes	17,351	48,024
Deferred income tax benefit due to tax legislation	(73,784)	0
Manufactured gas plant remediation costs	(13,624)	(6,923)
Equity in earnings, net of distributions received from equity investees	(935)	(334)
Cost of removal - asset retirement obligations	(93)	(363)
Contributions to postemployment benefit plans	(4,708)	(4,640)
Tax benefit from stock-based compensation	2,841	1,284
Changes in:
Components of working capital	64,527	(26,843)
Other noncurrent assets	41,793	27,930
Other noncurrent liabilities	13,224	7,668
Cash flows from operating activities	392,557	223,096
Expenditures for:
Utility plant	(130,727)	(92,833)
Solar and wind equipment	(88,416)	(121,958)
Midstream and other	(4,879)	(933)
Cost of removal	(42,683)	(23,001)
Investments in equity investees	(14,496)	(24,097)
Distribution from equity investees in excess of equity in earnings	2,515	2,179
Cash paid related to acquisition	(10,000)	0
(Deposits to) withdrawal from restricted cash construction fund	(52)	1,302
Proceeds from sale of property, net of closing costs	0	9,443
Proceeds from sale of businesses, net of closing costs	27,916	0
Proceeds from sale of available for sale securities, net	6,616	6,639
Cash flows used in investing activities	(254,206)	(243,259)
CASH FLOWS (USED IN) FROM FINANCING ACTIVITIES
Proceeds from long-term debt	225,000	0
Payments of long-term debt	(133,717)	(43,454)
(Payments of) proceeds from short-term debt, net	(208,900)	141,700
Proceeds from sale-leaseback transaction	7,820	9,587
Payments of common stock dividends	(71,334)	(65,909)
Proceeds from waiver discount issuance of common stock	41,677	0
Proceeds from issuance of common stock	13,572	13,802
Purchases of treasury stock	0	(6,355)
Tax withholding payments related to net settled stock compensation	(13,625)	(4,595)
Cash flows (used in) from financing activities	(139,507)	44,776
Change in cash and cash equivalents	(1,156)	24,613
Cash and cash equivalents at beginning of period	2,226	37,546
Cash and cash equivalents at end of period	1,070	62,159
CHANGES IN COMPONENTS OF WORKING CAPITAL
Receivables	(5,757)	(26,487)
Inventories	63,838	4,003
Recovery of gas costs	28,524	(4,610)
Gas purchases payable	28,041	11,929
Prepaid and accrued taxes	(22,993)	(22,820)
Accounts payable and other	5,213	(3,973)
Restricted broker margin accounts	(29,497)	27,314
Customers' credit balances and deposits	(745)	(12,873)
Other current assets	(2,097)	674
Components of working capital	64,527	(26,843)
Cash paid (received) for:
Interest (net of amounts capitalized)	35,295	30,128
Income taxes	4,195	(4,178)
Accrued capital expenditures	30,019	32,826
Inception gain on natural gas swap contract recognized as non-cash proceeds from sale of business	$ 14,579	$ 0