Consolidated Statements Of Cash Flows (USD $) In Thousands, unless otherwise specified	6 Months Ended
	Mar. 31, 2013	Mar. 31, 2012
Operating Activities
Net Income Available for Common Stock	$ 153,664	$ 128,091
Adjustments to Reconcile Net Income to Net Cash Provided by Operating Activities:
Depreciation, Depletion and Amortization	152,361	125,698
Deferred Income Taxes	102,557	81,696
Excess Tax Benefits Associated with Stock-Based Compensation Awards	0	(1,076)
Other	14,609	4,269
Change in:
Hedging Collateral Deposits	(386)	829
Receivables and Unbilled Utility Revenue	(109,403)	(50,906)
Gas Stored Underground and Materials and Supplies	32,391	37,156
Other Current Assets	4,389	5,038
Accounts Payable	20,456	(10,933)
Amounts Payable to Customers	(1,725)	1,808
Customer Advances	(23,910)	(19,439)
Customer Security Deposits	(804)	(300)
Other Accruals and Current Liabilities	39,273	59,250
Other Assets	(6,200)	(5,555)
Other Liabilities	(10,417)	994
Net Cash Provided by Operating Activities	366,855	356,620
Investing Activities
Capital Expenditures	(339,737)	(517,330)
Other	(3,445)	(789)
Net Cash Used in Investing Activities	(343,182)	(518,119)
Financing Activities
Changes in Notes Payable to Banks and Commercial Paper	(171,000)	(20,000)
Excess Tax Benefits Associated with Stock-Based Compensation Awards	0	1,076
Net Proceeds from Issuance of Long-Term Debt	495,415	496,085
Reduction of Long-Term Debt	(250,000)	(150,000)
Dividends Paid on Common Stock	(60,879)	(58,877)
Net Proceeds from Issuance of Common Stock	710	5,030
Net Cash Provided by Financing Activities	14,246	273,314
Net Increase in Cash and Temporary Cash Investments	37,919	111,815
Cash and Temporary Cash Investments at October 1	74,494	80,428
Cash and Temporary Cash Investments at March 31	$ 112,413	$ 192,243