Loans and Allowance for Loan Losses - Additional information (Details)	9 Months Ended	12 Months Ended
Mar. 31, 2021 USD ($) loan	Jun. 30, 2020 loan
Loans and Allowance for Loan Losses
TDR's granted during the period \| loan	2	1
TDR investment modified during the period \| $	$ 105,000
TDR's defaulted during the period \| $	0
TDR granted and subsequently transferred out of TDR status during the period \| loan	1

Number of financing receivables that have been modified by troubled debt restructurings and subsequently transferred out of TDR status during the period.

No definition available.

+ Details

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Namespace Prefix:	tbba_
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Balance Type:	na
Period Type:	duration

- Definition

Amount of financing receivable modified as troubled debt restructuring during the period.

+ References

No definition available.

+ Details

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Namespace Prefix:	tbba_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Number of financing receivables that have been modified by troubled debt restructurings.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 33
-URI http://asc.fasb.org/extlink&oid=118936363&loc=SL6953676-111524

+ Details

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Balance Type:	na
Period Type:	duration

- Definition

Number of financing receivable contracts modified as troubled debt restructuring within previous 12 months, with subsequent payment default.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 34
-URI http://asc.fasb.org/extlink&oid=118936363&loc=SL6953682-111524

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

- References

No definition available.

+ Details

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Balance Type:	na
Period Type:	duration