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Employee Benefit Plan - Additional Information (Details) - USD ($) $ in Thousands | 12 Months Ended
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Dec. 31, 2021 | Dec. 31, 2020 | Dec. 31, 2019
Retirement Benefits [Abstract] |  |  |
Employee minimum service period | 3 months |  |
Eligibility age of employees for plan | 18 years |  |
Employer contribution amount | $ 752 | $ 691 | $ 602

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- Definition Eligibility age of employees for plan. + References No definition available. + Details
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Namespace Prefix: | opbk_
Data Type: | xbrli:durationItemType
Balance Type: | na
Period Type: | duration

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- Definition Employee minimum service period. + References No definition available. + Details
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Namespace Prefix: | opbk_
Data Type: | xbrli:durationItemType
Balance Type: | na
Period Type: | duration

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

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- Definition Amount of discretionary contributions made by an employer to a defined contribution plan. + References No definition available. + Details
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Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
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