Capitalization and Short-Term Borrowings (Summary of Changes in Common Stock Equity) (Details) - USD ($) $ / shares in Units, $ in Thousands		3 Months Ended
		Dec. 31, 2020	Dec. 31, 2019
Schedule of Capitalization, Equity [Line Items]
Beginning balance (shares)		90,954,696
Beginning balance		$ 1,004,158
Balance at Beginning of Period		991,630	$ 1,272,601
Balance at Beginning of Period		(114,757)	(52,155)
Net Income Available for Common Stock		77,774	86,591
Dividends Declared on Common Stock		(40,560)	(37,650)
Other Comprehensive Income (Loss), Net of Tax		$ 35,016	(3,995)
Ending balance (shares)		91,152,710
Ending balance		$ 1,004,369
Balance at December 31		1,028,844	1,320,592
Balance at End of Period		$ (79,741)	$ (56,150)
Dividends per share		$ 0.445	$ 0.435
Paid-in Capital [Member]
Schedule of Capitalization, Equity [Line Items]
Beginning balance		$ 1,004,158	$ 832,264
Share-Based Payment Expense	[1]	3,496	2,828
Common Stock Repurchased under Stock and Benefit Plans		(3,285)	(3,946)
Ending balance		1,004,369	831,146
Earnings Reinvested in The Business [Member]
Schedule of Capitalization, Equity [Line Items]
Balance at Beginning of Period		991,630	1,272,601
Net Income Available for Common Stock		77,774	86,591
Dividends Declared on Common Stock		(40,560)	(37,650)
Balance at December 31		1,028,844	1,320,592
Accumulated Other Comprehensive Income (Loss) [Member]
Schedule of Capitalization, Equity [Line Items]
Balance at Beginning of Period		(114,757)	(52,155)
Other Comprehensive Income (Loss), Net of Tax		35,016	(3,995)
Balance at End of Period		$ (79,741)	$ (56,150)
Common Stock [Member]
Schedule of Capitalization, Equity [Line Items]
Beginning balance (shares)		90,955,000	86,315,000
Beginning balance (value)		$ 90,955	$ 86,315
Common Stock Issued Under Stock and Benefit Plans (Shares)		198,000	237,000
Common Stock Issued Under Stock and Benefit Plans (Value)		$ 198	$ 237
Ending balance (shares)		91,153,000	86,552,000
Ending balance (value)		$ 91,153	$ 86,552
Guidance for Hedging [Member] | Cumulative Effect of Adoption of Authoritative Guidance [Member]
Schedule of Capitalization, Equity [Line Items]
Balance at Beginning of Period		$ 0	(950)
Guidance for Hedging [Member] | Earnings Reinvested in The Business [Member] | Cumulative Effect of Adoption of Authoritative Guidance [Member]
Schedule of Capitalization, Equity [Line Items]
Balance at Beginning of Period			$ (950)

[1] Paid in Capital includes compensation costs associated with performance shares and/or restricted stock awards. The expense is included within Net Income Available For Common Stock, net of tax benefits.