Mortgage Loans - Loan Commitments and Related Derivatives Textual (Details) - USD ($) $ in Millions	Sep. 30, 2018	Sep. 30, 2017
Interest rate lock commitments [Member]
Derivative [Line Items]
Notional amount	$ 485.3	$ 446.2
Best-efforts whole loan delivery commitments [Member]
Derivative [Line Items]
Notional amount	25.6	26.9
Hedging Instruments Related To IRLCs [Member]
Derivative [Line Items]
Notional amount	$ 430.2	$ 389.3