Allowance for credit losses change in method of calculating impairments.

No definition available.

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Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Financing receivable number of draw loans.

+ References

No definition available.

+ Details

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

- Definition

Financing receivable number of loans balance.

+ References

No definition available.

+ Details

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Namespace Prefix:	opbk_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant

- Definition

Financing receivable, number of loans originated.

+ References

No definition available.

+ Details

Name:	opbk_FinancingReceivableNumberOfLoansOriginated
Namespace Prefix:	opbk_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant

- Definition

Impaired financing receivable, accrued interest receivable.

+ References

No definition available.

+ Details

Name:	opbk_ImpairedFinancingReceivableAccruedInterestReceivable
Namespace Prefix:	opbk_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Loans and leases receivable amount funded.

+ References

No definition available.

+ Details

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Namespace Prefix:	opbk_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Loans and leases receivable draw amount.

+ References

No definition available.

+ Details

Name:	opbk_LoansAndLeasesReceivableDrawAmount
Namespace Prefix:	opbk_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Number of processed loan deferments.

+ References

No definition available.

+ Details

Name:	opbk_NumberOfProcessedLoanDeferments
Namespace Prefix:	opbk_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant

- Definition

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

+ References

+ Details

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Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

- Definition

Amount of financing receivable modified as troubled debt restructuring.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 33
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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

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

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 34
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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

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

- Definition

For an unclassified balance sheet, reflects the carrying amount of unpaid loan amounts due from related parties at the balance sheet date.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 850
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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Amount, before allowance for credit loss, of financing receivable.

+ References

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 326
-SubTopic 20
-Section 55
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+ Details

Name:	us-gaap_NotesReceivableGross
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Details

Name:	us-gaap_LoansInsuredOrGuaranteedByGovernmentAuthoritiesAxis=opbk_FirstDrawOfSBAPaycheckProtectionProgramLoansMember
Namespace Prefix:
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Balance Type:
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- Details

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- Details

Name:	us-gaap_FinancingReceivablePortfolioSegmentAxis=opbk_HomeMortgagePortfolioMember
Namespace Prefix:
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Balance Type:
Period Type:

- Details

Name:	us-gaap_LoanRestructuringModificationAxis=us-gaap_PaymentDeferralMember
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Loans - Additional Information (Details)	3 Months Ended
Loans - Additional Information (Details)	Mar. 31, 2021 USD ($) Contract loan	Mar. 31, 2020 USD ($) Contract	Dec. 31, 2020 USD ($)
Loans And Leases Receivable Disclosure [Line Items]
Loans	$ 0		$ 0
Accrued interest receivable	4,100,000		4,400,000
Recorded investment in troubled debt restructurings	327,000		330,000
Specific reserves to customers whose loan terms have been modified in TDRs	$ 327,000		330,000
Loans identified as TDRs \| Contract	0	0
Financing receivable, modifications, subsequent default, recorded investment	$ 0	$ 0
Loans aggregate balance	$ 1,159,990,000		1,104,108,000
First Draw of SBA PPP Loans
Loans And Leases Receivable Disclosure [Line Items]
Number of loans originated \| loan	978
Total loans funded	$ 66,300,000
Loans forgiven	$ 22,900,000
Number of loans forgiven \| loan	429
Second Draw of SBA PPP Loans
Loans And Leases Receivable Disclosure [Line Items]
Number of loans originated \| loan	1,336
Total loans funded	$ 74,200,000
Home Mortgage
Loans And Leases Receivable Disclosure [Line Items]
Loans aggregate balance	125,759,000		$ 128,683,000
Payment Deferral
Loans And Leases Receivable Disclosure [Line Items]
Recorded investment in troubled debt restructurings	$ 236,787,000
Number of processed loan deferments \| loan	185
Number of loans \| loan	171
Loans aggregate balance	$ 217,797,000
Payment Deferral \| Home Mortgage
Loans And Leases Receivable Disclosure [Line Items]
Recorded investment in troubled debt restructurings	$ 30,205,000
Number of processed loan deferments \| loan	69
Number of loans \| loan	64
Loans aggregate balance	$ 27,444,000