Mortgage Loans - Loan Commitments and Related Derivatives Textual (Details) - USD ($) $ in Millions	Sep. 30, 2019	Sep. 30, 2018
Interest rate lock commitments [Member]
Derivative [Line Items]
Derivative, Notional Amount	$ 727.9	$ 485.3
Best-efforts whole loan delivery commitments [Member]
Derivative [Line Items]
Derivative, Notional Amount	25.2	25.6
Hedging Instruments Related To IRLCs [Member]
Derivative [Line Items]
Derivative, Notional Amount	636.2	430.2
Loan Origination Commitments [Member]
Derivative [Line Items]
Derivative, Notional Amount	111.4
Fair Value, Inputs, Level 2 [Member] \| Fair Value, Recurring [Member] \| Interest rate lock commitments [Member]
Derivative [Line Items]
Interest Rate Derivative Instruments Not Designated as Hedging Instruments at Fair Value, Net	19.2	10.5
Fair Value, Inputs, Level 2 [Member] \| Fair Value, Recurring [Member] \| Best-efforts whole loan delivery commitments [Member]
Derivative [Line Items]
Interest Rate Derivative Instruments Not Designated as Hedging Instruments at Fair Value, Net	(1.0)	0.2
Fair Value, Inputs, Level 2 [Member] \| Fair Value, Recurring [Member] \| Hedging Instruments Related To IRLCs [Member]
Derivative [Line Items]
Interest Rate Derivative Instruments Not Designated as Hedging Instruments at Fair Value, Net	(4.1)	$ 3.3
Fair Value, Inputs, Level 2 [Member] \| Fair Value, Recurring [Member] \| Loan Origination Commitments [Member]
Derivative [Line Items]
Interest Rate Derivative Instruments Not Designated as Hedging Instruments at Fair Value, Net	$ (0.5)

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Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
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-URI http://asc.fasb.org/extlink&oid=117331979&loc=d3e41228-113958

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