CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS (Unaudited) - USD ($) $ in Thousands	6 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
CASH FLOWS FROM OPERATING ACTIVITIES
Net income	$ 149,631	$ 123,635
Adjustments to reconcile net income to cash flows from operating activities
Unrealized (gain) loss on derivative instruments	(26,553)	2,035
Gain on sale of property and available for sale securities, net	7,287	0
Depreciation and amortization	39,588	34,226
Allowance for equity used during construction	(1,586)	(2,357)
Allowance for bad debt expense	519	873
Deferred income taxes	32,202	17,980
Manufactured gas plant remediation costs	(3,704)	(2,656)
Distributions received from equity investees, net of equity in earnings	(463)	2,261
Cost of removal - asset retirement obligations	(242)	(66)
Contributions to postemployment benefit plans	(1,884)	(32,167)
Tax benefit from stock-based compensation	1,231	1,660
Changes in:
Components of working capital	(31,231)	(13,788)
Other noncurrent assets	24,580	(15,794)
Other noncurrent liabilities	(2,997)	2,163
Cash flows from operating activities	171,804	118,005
CASH FLOWS (USED IN) INVESTING ACTIVITIES
Utility plant	(58,761)	(76,326)
Solar and wind equipment	(89,905)	(70,882)
Real estate properties and other	(516)	(1,069)
Cost of removal	(14,838)	(20,080)
Investments in equity investees	(10,538)	(5,948)
Distribution from equity investees in excess of equity in earnings	1,273	1,131
Withdrawal from restricted cash construction fund	1,337	1,007
Proceeds from sale of property, net of closing costs	9,443	748
Proceeds from sale of available for sale securities	6,639	0
Cash flows (used in) investing activities	(155,866)	(171,419)
CASH FLOWS FROM FINANCING ACTIVITIES
Net proceeds from short-term debt	116,200	86,150
Payments of long-term debt	(41,660)	(5,807)
Proceeds from sale-leaseback transaction	9,587	7,107
Payments of common stock dividends	(43,898)	(41,115)
Proceeds from issuance of common stock	9,731	8,220
Purchases of treasury stock	(6,355)	(1,008)
Tax withholding payments related to net settled stock compensation	(4,354)	(3,181)
Cash flows from financing activities	39,251	50,366
Change in cash and cash equivalents	55,189	(3,048)
Cash and cash equivalents at beginning of period	37,546	4,928
Cash and cash equivalents at end of period	92,735	1,880
CHANGES IN COMPONENTS OF WORKING CAPITAL
Receivables	(137,408)	(16,750)
Inventories	62,321	43,479
Recovery of gas costs	(9,616)	(20,396)
Gas purchases payable	21,156	(31,324)
Gas purchases payable - related parties	3	(409)
Prepaid and accrued taxes	25,829	43,154
Accounts payable and other	(10,027)	(25,026)
Restricted broker margin accounts	28,432	(12,478)
Customers' credit balances and deposits	(12,765)	226
Other current assets	844	5,736
Components of working capital	(31,231)	(13,788)
Cash paid (received) for:
Interest (net of amounts capitalized)	21,578	15,647
Income taxes	(6,431)	688
Accrued capital expenditures	$ 23,284	$ 21,663