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Fair Value Measurements - Additional Information (Details) - USD ($) | 9 Months Ended | 12 Months Ended
--- | --- | ---
Sep. 30, 2017 | Dec. 31, 2016
Fair Value Disclosures [Abstract] |  |
Write-downs to OREO | $ 0 | $ 0

X
- Definition Write down on other real estate owned. + References No definition available. + Details
Name: | rbb_WriteDownOnOtherRealEstateOwned
Namespace Prefix: | rbb_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- References No definition available. + Details
Name: | us-gaap_FairValueDisclosuresAbstract
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration