Consolidated Statements Of Income And Earnings Reinvested In The Business (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended		6 Months Ended
	Mar. 31, 2013	Mar. 31, 2012	Mar. 31, 2013	Mar. 31, 2012
INCOME
Operating Revenues	$ 597,826	$ 552,309	$ 1,050,680	$ 984,732
Operating Expenses
Purchased Gas	209,817	208,537	331,735	340,730
Operation and Maintenance	122,303	118,047	230,035	218,106
Property, Franchise and Other Taxes	22,685	30,477	42,348	49,707
Depreciation, Depletion and Amortization	80,030	63,151	152,361	125,698
Total Operating Expenses	434,835	420,212	756,479	734,241
Operating Income	162,991	132,097	294,201	250,491
Other Income (Expense):
Interest Income	140	192	1,526	1,297
Other Income	1,087	1,654	2,501	2,990
Interest Expense on Long-Term Debt	(22,786)	(20,425)	(44,234)	(39,066)
Other Interest Expense	(526)	(1,253)	(1,595)	(2,023)
Income Before Income Taxes	140,906	112,265	252,399	213,689
Income Tax Expense	55,186	44,873	98,735	85,598
Net Income Available for Common Stock	85,720	67,392	153,664	128,091
EARNINGS REINVESTED IN THE BUSINESS
Balance at Beginning of Period	1,343,765	1,237,242	1,306,284	1,206,022
Beginning Retained Earnings Unappropriated And Current Period Net Income Loss	1,429,485	1,304,634	1,459,948	1,334,113
Dividends on Common Stock	(30,486)	(29,527)	(60,949)	(59,006)
Balance at March 31	$ 1,398,999	$ 1,275,107	$ 1,398,999	$ 1,275,107
Earnings Per Common Share, Basic:
Net Income Available for Common Stock	$ 1.03	$ 0.81	$ 1.84	$ 1.54
Diluted:
Net Income Available for Common Stock	$ 1.02	$ 0.81	$ 1.83	$ 1.53
Weighted Average Common Shares Outstanding:
Used in Basic Calculation	83,498,508	83,107,884	83,443,805	82,988,750
Used in Diluted Calculation	84,159,734	83,678,261	84,127,705	83,712,681
Dividends Per Common Share:
Dividends Declared	$ 0.365	$ 0.355	$ 0.73	$ 0.71