Consolidated Statements Of Income And Earnings Reinvested In The Business (USD $) In Thousands, except Share data, unless otherwise specified	12 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2012
INCOME
Operating Revenues	$ 2,113,081	$ 1,829,551	$ 1,626,853
Operating Expenses
Purchased Gas	605,838	460,432	415,589
Operation and Maintenance	463,078	442,090	401,397
Property, Franchise and Other Taxes	90,711	82,431	90,288
Depreciation, Depletion and Amortization	383,781	326,760	271,530
Total Operating Expenses	1,543,408	1,311,713	1,178,804
Operating Income	569,673	517,838	448,049
Other Income (Expense):
Other Income	9,461	4,697	5,133
Interest Income	4,170	4,335	3,689
Interest Expense on Long-Term Debt	(90,194)	(90,273)	(82,002)
Other Interest Expense	(4,083)	(3,838)	(4,238)
Income Before Income Taxes	489,027	432,759	370,631
Income Tax Expense	189,614	172,758	150,554
Net Income Available for Common Stock	299,413	260,001	220,077
EARNINGS REINVESTED IN THE BUSINESS
Balance at Beginning of Year	1,442,617	1,306,284	1,206,022
Beginning Retained Earnings Unappropriated And Current Period Net Income Loss	1,742,030	1,566,285	1,426,099
Dividends on Common Stock	(127,669)	(123,668)	(119,815)
Balance at End of Year	$ 1,614,361	$ 1,442,617	$ 1,306,284
Earnings Per Common Share, Basic:
Net Income Available for Common Stock (in usd per share)	$ 3.57	$ 3.11	$ 2.65
Earnings Per Common Share, Diluted:
Net Income Available for Common Stock (in usd per share)	$ 3.52	$ 3.08	$ 2.63
Weighted Average Number of Shares Outstanding:
Used in Basic Calculation	83,929,989	83,518,857	83,127,844
Used in Diluted Calculation	84,952,347	84,341,220	83,739,771