Investment Securities: Schedule of significant inputs utilized to measure management's estimate of the credit loss component on OTTI securities (Details) - USD ($) $ in Thousands	3 Months Ended	6 Months Ended
Mar. 31, 2019	Mar. 31, 2018	Mar. 31, 2019	Mar. 31, 2018
Other than Temporary Impairment, Credit Losses Recognized in Earnings [Line Items]
Recoveries (other than temporary impairment OTTI) on investment securities	$ (20)	$ (14)	$ (32)	$ (41)
Net recoveries on investment securities	(9)	(14)	(20)	(36)
Held-to-maturity Securities
Other than Temporary Impairment, Credit Losses Recognized in Earnings [Line Items]
Recoveries (other than temporary impairment OTTI) on investment securities	20	14	32	41
Held to Maturity - adjustment for portion of OTTI recorded as OCI before income taxes	(11)	0	(12)	(5)
Net recoveries on investment securities	9	14	20	36
Available-for-sale Securities
Other than Temporary Impairment, Credit Losses Recognized in Earnings [Line Items]
AFS - OTTI	0	0	0	0
AFS - - adjustment for portion of OTTI recorded as OCI before income taxes	0	0	0	0
AFS - Net OTTI recognized in earnings	$ 0	$ 0	$ 0	$ 0
Minimum
Other than Temporary Impairment, Credit Losses Recognized in Earnings [Line Items]
OTTI significant inputs - Constant prepayment rate	6.00%	6.00%	6.00%	6.00%
OTTI significant inputs - Collateral default rate	0.00%	0.00%	0.00%	0.00%
OTTI significant inputs - Loss severity rate	0.00%	0.00%	0.00%	0.00%
Maximum
Other than Temporary Impairment, Credit Losses Recognized in Earnings [Line Items]
OTTI significant inputs - Constant prepayment rate	15.00%	15.00%	15.00%	15.00%
OTTI significant inputs - Collateral default rate	16.06%	11.85%	16.06%	11.85%
OTTI significant inputs - Loss severity rate	78.00%	72.00%	78.00%	72.00%
Weighted Average
Other than Temporary Impairment, Credit Losses Recognized in Earnings [Line Items]
OTTI significant inputs - Constant prepayment rate	10.24%	11.01%	10.24%	11.01%
OTTI significant inputs - Collateral default rate	5.20%	5.04%	5.20%	5.04%
OTTI significant inputs - Loss severity rate	40.02%	38.32%	40.02%	38.32%

Marketable Securities, Realized Losses (Recoveries), Other than Temporary Impairments, Amount

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Other than Temporary Impairment Losses (Recoveries), Investments, Portion Recognized in Earnings, Net

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 45
-Paragraph 8A
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Amount before tax of other than temporary impairment (OTTI) on investment in held-to-maturity debt security, recognized in other comprehensive loss.

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The amount of other than temporary impairment losses on investments in debt and equity securities categorized as Available-for-sale which have been recognized in earnings during the period. Such impairment losses consist of other than temporary impairments (OTTI) on equity securities, credit losses on investments in debt securities, and when the entity intends to sell an impaired debt security or it is more likely than not that the entity will be required to sell the impaired debt security before recovery of its amortized cost basis.

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