Loans Receivable - Loan Modifications (Details) $ in Thousands	3 Months Ended		9 Months Ended
	Jun. 30, 2018 USD ($) contract	Jun. 30, 2017 USD ($) contract	Jun. 30, 2018 USD ($) contract	Jun. 30, 2017 USD ($) contract
Financing Receivable, Modifications [Line Items]
Number of Contracts | contract	0	3	2	18
Recorded Investment | $	$ 0	$ 401	$ 206	$ 3,853
Single-family residential
Financing Receivable, Modifications [Line Items]
Number of Contracts | contract	0	3	2	16
Recorded Investment | $	$ 0	$ 401	$ 206	$ 3,586
Commercial real estate
Financing Receivable, Modifications [Line Items]
Number of Contracts | contract			0	2
Recorded Investment | $			$ 0	$ 267