Represents percentage of employees ownership plan interest rate.

No definition available.

Name:	rbkb_EmployeeOwnershipPlanEsopRateOfInterest
Namespace Prefix:	rbkb_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Represents amount related to fair value of unallocated shares.

+ References

No definition available.

+ Details

Name:	rbkb_EmployeeStockOwnershipPlanEsopAmountOfUnallocatedShares
Namespace Prefix:	rbkb_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Represents number of term related to employee stock ownership plan.

+ References

No definition available.

+ Details

Name:	rbkb_EmployeeStockOwnershipPlanEsopTermsOfRepurchase
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://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 40
-Section 50
-Paragraph 1
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=109244661&loc=d3e17540-113929

+ Details

Name:	us-gaap_EmployeeStockOwnershipPlanESOPCompensationExpense
Namespace Prefix:	us-gaap_
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://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 40
-Section 25
-Paragraph 9
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=109244457&loc=d3e16545-113920

+ Details

Name:	us-gaap_EmployeeStockOwnershipPlanESOPDebtStructureDirectLoanAmount
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
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

No definition available.

+ Details

Name:	us-gaap_EmployeeStockOwnershipPlanESOPDisclosuresLineItems
Namespace Prefix:	us-gaap_
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://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 40
-Section 50
-Paragraph 1
-Subparagraph (d)
-URI http://asc.fasb.org/extlink&oid=109244661&loc=d3e17540-113929

+ Details

Name:	us-gaap_EmployeeStockOwnershipPlanESOPNumberOfCommittedToBeReleasedShares
Namespace Prefix:	us-gaap_
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

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 40
-Section 50
-Paragraph 1
-Subparagraph (d)
-URI http://asc.fasb.org/extlink&oid=109244661&loc=d3e17540-113929

+ Details

Name:	us-gaap_EmployeeStockOwnershipPlanESOPSharesInESOP
Namespace Prefix:	us-gaap_
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

Name:	us-gaap_SharePrice
Namespace Prefix:	us-gaap_
Data Type:	num:perShareItemType
Balance Type:	na
Period Type:	instant

- Details

Name:	us-gaap_EmployeeStockOwnershipPlanESOPDisclosuresByPlanAxis=rbkb_EmployeeStockOwnershipPlanEsopMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Employee Benefits (Detail Textuals 1) - USD ($) $ / shares in Units, $ in Thousands	1 Months Ended	6 Months Ended	12 Months Ended
	Jan. 16, 2019	Jun. 30, 2019	Dec. 31, 2018
Employee Stock Ownership Plan (ESOP) Disclosures [Line Items]
Number of share purchase under ESOP		436,425
Committed to be allocated		10,910
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	$ 10.00
Terms of repurchase share under ESOP	20 years
Interest rate			5.50%
Balance of ESOP loan		$ 4,400
Committed to be allocated		21,821
Fair value of unallocated shares		$ 4,700
Compensation expense		$ 183