Derivative Financial Instruments - CF Hedges (Details) - Cash Flow Hedges - USD ($) $ in Millions	Sep. 30, 2013	Apr. 30, 2011	Oct. 31, 2009
Interest Rate Swaps
Fair values of derivative financial instruments
Fixed rate (as a percent)	1.819%		3.93%
Interest Rate Swaps | London Interbank Offered Rate (LIBOR) [Member]
Fair values of derivative financial instruments
Hedged borrowings	$ 100.0		$ 100.0
Interest Rate Cap
Fair values of derivative financial instruments
Maximum cap rate (as a percent)		5.50%
Interest Rate Cap | London Interbank Offered Rate (LIBOR) [Member]
Fair values of derivative financial instruments
Hedged borrowings		$ 100.0