Represents percentage of employees ownership plan interest rate.

No definition available.

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Namespace Prefix:	rbkb_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Represents number of term related to employee stock ownership plan.

+ References

No definition available.

+ Details

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Namespace Prefix:	rbkb_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

The amount of plan compensation cost recognized during the period.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

The amount reported as a liability as of the balance sheet date by the entity (the employer) of the loan made by a third-party lender directly to the ESOP.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 718
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-Section 25
-Paragraph 9
-Subparagraph (a)
-Publisher FASB
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+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Fair value of unearned shares held by the employee stock ownership plan (ESOP).

+ References

Reference 1: http://www.xbrl.org/2003/role/exampleRef
-Topic 718
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Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
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Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

The shares that, although not legally released, will be released by a future scheduled and committed debt service payment and will be allocated to employees for service rendered in the current accounting period. The ESOP documents typically define the period of service to which the shares relate. ESOP shares are released to compensate employees directly, to settle employer liabilities for other employee benefits, and to replace dividends on allocated shares that are used for debt service.

+ References

Reference 1: http://www.xbrl.org/2003/role/exampleRef
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+ Details

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Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	instant

- Definition

Sum of the allocated, committed-to-be-released and suspense shares of the entity held by the plan.

+ References

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-Topic 718
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Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	instant

- Definition

Price of a single share of a number of saleable stocks of a company.

+ References

No definition available.

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	dtr-types:perShareItemType
Balance Type:	na
Period Type:	instant

- Details

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Period Type:

Employee Benefits (Employee Stock Ownership Plan (ESOP) Narrative) (Details) - USD ($) $ / shares in Units, $ in Thousands		1 Months Ended	3 Months Ended		9 Months Ended
	Jan. 01, 2025	Jan. 16, 2019	Sep. 30, 2025	Sep. 30, 2024	Sep. 30, 2025	Sep. 30, 2024	Dec. 31, 2024
Employee Stock Ownership Plan (ESOP) Disclosures [Line Items]
Number of share purchase under ESOP			412,803		412,803		412,803
Committed to be allocated			16,362		16,362		21,821
Compensation expense					$ 184	$ 135
Employee Stock Ownership Plan (ESOP)
Employee Stock Ownership Plan (ESOP) Disclosures [Line Items]
Number of share purchase under ESOP		436,425
Common stock price per share		$ 10
Terms of repurchase share under ESOP		20 years
Interest rate	7.50%
Balance of ESOP loan			$ 3,484		$ 3,484
Committed to be allocated			21,821		21,821
Fair value of unallocated shares			$ 3,285		$ 3,285
Compensation expense			$ 69	$ 45	$ 184	$ 134