Capitalization (Details) - USD ($) $ in Thousands	6 Months Ended
	Mar. 31, 2018	Sep. 30, 2017
Debt Instrument [Line Items]
Common stock shares issued due to SARs exercises	64,085
Issue shares of common stock for the Direct Stock Purchase and Dividend Reinvestment Plan	109,535
Issue shares of common stock for the 401(k) plans	55,280
Shares tendered	51,574
Current Portion of Long-Term Debt	$ 0	$ 300,000
Debt Instrument Redeemed	$ 307,000
Restricted Stock Units [Member]
Debt Instrument [Line Items]
Common stock issued	68,534
Performance Shares [Member]
Debt Instrument [Line Items]
Common stock issued	79,079
Board Of Directors [Member]
Debt Instrument [Line Items]
Common stock issued	13,833
6.50% Notes Due April 2018 [Member]
Debt Instrument [Line Items]
Current Portion of Long-Term Debt		$ 300,000
Long-term debt, interest rate		6.50%