Consolidated Statements Of Income And Earnings Reinvested In The Business (Unaudited) - USD ($) $ in Thousands	3 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
INCOME
Operating Revenues	$ 490,247	$ 419,655
Operating Expenses:
Property, Franchise and Other Taxes	24,005	20,848
Depreciation, Depletion and Amortization	64,255	55,830
Total Operating Expenses	328,564	270,186
Operating Income	161,683	149,469
Other Income (Expense):
Other Income (Deductions)	(9,602)	(3,503)
Interest Expense on Long-Term Debt	(25,439)	(28,087)
Other Interest Expense	(1,073)	(502)
Income Before Income Taxes	125,569	117,377
Income Tax Expense (Benefit)	22,909	(81,277)
Net Income Available for Common Stock	102,660	198,654
EARNINGS REINVESTED IN THE BUSINESS
Balance at Beginning of Period	1,098,900	851,669
Beginning Retained Earnings Unappropriated And Current Period Net Income	1,201,560	1,050,323
Dividends on Common Stock	(36,663)	(35,590)
Balance at December 31	$ 1,172,334	$ 1,014,733
Earnings Per Common Share, Basic:
Net Income Available for Common Stock (in dollars per share)	$ 1.19	$ 2.32
Earnings Per Common Share, Diluted:
Net Income Available for Common Stock (in dollars per share)	$ 1.18	$ 2.30
Weighted Average Common Shares Outstanding:
Used in Basic Calculation (shares)	86,032,729	85,630,296
Used in Diluted Calculation (shares)	86,708,814	86,325,537
Dividends Per Common Share:
Dividends Declared (in dollars per share)	$ 0.425	$ 0.415
Purchased Gas [Member]
Operating Expenses:
Purchased Gas	$ 138,660	$ 94,034
Utility and Energy Marketing [Member]
INCOME
Operating Revenues	272,092	225,725
Operating Expenses:
Operation and Maintenance	43,915	44,080
Exploration and Production and Other [Member]
INCOME
Operating Revenues	163,937	140,450
Operating Expenses:
Operation and Maintenance	32,795	35,083
Pipeline and Storage and Gathering [Member]
INCOME
Operating Revenues	54,218	53,480
Operating Expenses:
Operation and Maintenance	24,934	20,311
Guidance for Recognition and Measurement of Financial Assets and Liabilities [Member]
EARNINGS REINVESTED IN THE BUSINESS
Cumulative Effect of Adoption of Authoritative Guidance for Financial Assets and Liabilities	$ 7,437	$ 0