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, 2020	Mar. 31, 2019	Mar. 31, 2020	Mar. 31, 2019
Other than Temporary Impairment, Credit Losses Recognized in Earnings [Line Items]
Recoveries (other than temporary impairment OTTI) on investment securities	$ (3)	$ (20)	$ (106)	$ (32)
Net recoveries on investment securities	(3)	(9)	(106)	(20)
Held-to-maturity Securities
Other than Temporary Impairment, Credit Losses Recognized in Earnings [Line Items]
Recoveries (other than temporary impairment OTTI) on investment securities	3	20	106	32
Held to Maturity - adjustment for portion of OTTI recorded as OCI before income taxes	0	(11)	0	(12)
Net recoveries on investment securities	3	9	106	20
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	1.86%	0.00%	1.86%	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	22.47%	16.06%	22.47%	16.06%
OTTI significant inputs - Loss severity rate	16.34%	78.00%	16.34%	78.00%
Weighted Average
Other than Temporary Impairment, Credit Losses Recognized in Earnings [Line Items]
OTTI significant inputs - Constant prepayment rate	10.91%	10.24%	10.91%	10.24%
OTTI significant inputs - Collateral default rate	10.44%	5.20%	10.44%	5.20%
OTTI significant inputs - Loss severity rate	4.02%	40.02%	4.02%	40.02%

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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The amount by which the fair value of an investment in debt and equity securities categorized as Available-for-sale is less than the amortized cost basis or carrying amount of that investment at the balance sheet date and the decline in fair value is deemed to be other than temporary, before considering whether or not such amount is recognized in earnings or other comprehensive income.

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Amount, before tax, of other-than-temporary impairment (OTTI) on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), recognized in other comprehensive income (OCI).

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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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