Capitalization (Narrative) (Details) (USD $)	6 Months Ended			6 Months Ended				0 Months Ended
	Mar. 31, 2012	Mar. 31, 2011	Dec. 01, 2011	Mar. 31, 2012 Direct Stock Purchase And Dividend Reinvestment Plan [Member]	Mar. 31, 2012 5.25% Notes Due in March 2013	Mar. 31, 2012 6.70% Medium-Term Notes November 2011 [Member]	Sep. 30, 2011 6.70% Medium-Term Notes November 2011 [Member]	Dec. 01, 2011 4.9% Notes Due In December 2021 [Member]
Schedule of Capitalization [Line Items]
Common stock shares issued due to stock option exercises	392,494
Issue shares of common stock for the Direct Stock Purchase and Dividend Reinvestment Plan				74,630
Shares issued for restricted stock	41,525
Common stock issued	7,986
Shares tendered	155,462
Current portion of long-term debt					$ 250,000,000	$ 150,000,000	$ 150,000,000
Percentage of principal amount			101.00%
Long-term debt, face value								500,000,000
Long-term debt, interest rate					5.25%	6.70%	6.70%	4.90%
Net proceeds from issuance of long-term debt	$ 496,085,000	$ 0						$ 496,100,000