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Loans Receivable - Loan Modifications (Details) $ in Thousands	3 Months Ended		6 Months Ended
	Mar. 31, 2019 USD ($) contract	Mar. 31, 2018 USD ($) contract	Mar. 31, 2019 USD ($) contract	Mar. 31, 2018 USD ($) contract
Financing Receivable, Modifications [Line Items]
Number of Contracts | contract	4	1	5	2
Recorded Investment | $	$ 755	$ 162	$ 1,298	$ 206
Single-family residential
Financing Receivable, Modifications [Line Items]
Number of Contracts | contract	4	1	5	2
Recorded Investment | $	$ 755	$ 162	$ 1,298	$ 206

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