Consolidated Statements Of Income And Earnings Reinvested In The Business (Unaudited) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended		6 Months Ended
	Mar. 31, 2014	Mar. 31, 2013	Mar. 31, 2014	Mar. 31, 2013
INCOME
Operating Revenues	$ 756,242	$ 597,826	$ 1,306,314	$ 1,050,680
Operating Expenses
Purchased Gas	322,772	209,817	490,378	331,735
Operation and Maintenance	137,716	122,303	245,562	230,035
Property, Franchise and Other Taxes	25,704	22,685	46,630	42,348
Depreciation, Depletion and Amortization	89,975	80,030	183,089	152,361
Total Operating Expenses	576,167	434,835	965,659	756,479
Operating Income	180,075	162,991	340,655	294,201
Other Income (Expense):
Interest Income	249	140	951	1,526
Other Income	5,123	1,087	5,352	2,501
Interest Expense on Long-Term Debt	(22,766)	(22,786)	(45,651)	(44,234)
Other Interest Expense	(1,375)	(526)	(2,324)	(1,595)
Income Before Income Taxes	161,306	140,906	298,983	252,399
Income Tax Expense	66,095	55,186	121,520	98,735
Net Income Available for Common Stock	95,211	85,720	177,463	153,664
EARNINGS REINVESTED IN THE BUSINESS
Balance at Beginning of Period	1,493,466	1,343,765	1,442,617	1,306,284
Beginning Retained Earnings Unappropriated And Current Period Net Income Loss	1,588,677	1,429,485	1,620,080	1,459,948
Dividends on Common Stock	(31,493)	(30,486)	(62,896)	(60,949)
Balance at March 31	$ 1,557,184	$ 1,398,999	$ 1,557,184	$ 1,398,999
Earnings Per Common Share, Basic:
Net Income Available for Common Stock (in dollars per share)	$ 1.14	$ 1.03	$ 2.12	$ 1.84
Earnings Per Common Share, Diluted:
Net Income Available for Common Stock (in dollars per share)	$ 1.12	$ 1.02	$ 2.09	$ 1.83
Weighted Average Common Shares Outstanding:
Used in Basic Calculation (shares)	83,856,120	83,498,508	83,781,085	83,443,805
Used in Diluted Calculation (shares)	84,837,123	84,159,734	84,787,610	84,127,705
Dividends Per Common Share:
Dividends Declared (in dollars per share)	$ 0.375	$ 0.365	$ 0.75	$ 0.73