Summary of Significant Accounting Policies: Cash (Details) - USD ($) $ in Thousands	12 Months Ended
Sep. 30, 2020	Sep. 30, 2019
Restricted Cash and Cash Equivalents Items [Line Items]
Interest-bearing deposits in Federal Reserve Bank	$ 292,575	$ 117,836
Minimum
Restricted Cash and Cash Equivalents Items [Line Items]
Maturity of CDs held for investment	12 months
Maximum
Restricted Cash and Cash Equivalents Items [Line Items]
Maturity of CDs held for investment	60 months
Interest-bearing deposits
Restricted Cash and Cash Equivalents Items [Line Items]
Interest-bearing deposits in Federal Reserve Bank	$ 266,171	$ 102,189

For banks and other depository institutions (including Federal Reserve Banks, if applicable): Interest-bearing deposits in other financial institutions for relatively short periods of time including, for example, certificates of deposits, which are presented separately from cash on the balance sheet.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section 45
-Paragraph 4
-URI http://asc.fasb.org/extlink&oid=117340910&loc=d3e59706-112781

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03.2)
-URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878

Name:	us-gaap_InterestBearingDepositsInBanks
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant