Financial Derivatives (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Sep. 30, 2013	Sep. 30, 2012
Notional Amount of Fair Value Hedge Instruments	$ 91.9	$ 34.1
Effective portion gain (loss) recorded in AOCI	12.6
7.5% Bonds [Member]
Description of Fair Value Hedge Activity	In conjunction with our 7.5% Bonds issued in June 2009, we executed $250.0 million notional value of interest rate swaps that exchange 7.5% fixed interest payments for variable rate interest payments, at one-month LIBOR plus 342 bps, reset two business days before the 15th of each month. In April 2011, we additionally executed $250.0 million notional value interest rate swaps that exchange the remaining fixed interest payments on these bonds for variable rate interest payments, based on six-month LIBOR plus 409 bps, reset in arrears two business days before June 15 and December 15 each year. All of these swaps terminate on June 15, 2019.
Derivative, Swaption Interest Rate (in hundredths)	7.50%
Notional Amount of Fair Value Hedge Instruments	250.0
5.5% Bonds [Member]
Description of Fair Value Hedge Activity	In conjunction with our 5.5% Bonds issued in June 2010, we executed $300.0 million notional value of interest rate swaps that terminate on June 15, 2020. These swaps effectively exchange 5.5% fixed interest payments for variable rate interest payments, based on the six-month LIBOR plus 186 bps, reset in arrears two business days before June 15 and December 15 each year. These swaps terminate on June 15, 2020.
Derivative, Swaption Interest Rate (in hundredths)	5.50%
Notional Amount of Fair Value Hedge Instruments	300.0
5.35% [Member]
Derivative, Swaption Interest Rate (in hundredths)	5.35%
Notional Amount of Fair Value Hedge Instruments	250.0
Maturity dates	August 15, 2013 and September 19, 2013
Effective portion gain (loss) recorded in AOCI	12.6
Effective portion gain (loss) recorded in AOCI, Tax	$ 4.6
Amortization period	10 years