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.

No definition available.

+ Details

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

- Definition

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

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 33
-URI https://asc.fasb.org/extlink&oid=123577603&loc=SL6953676-111524

+ Details

Name:	us-gaap_FinancingReceivableModificationsNumberOfContracts2
Namespace Prefix:	us-gaap_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

- Definition

Amount, after troubled debt restructuring, of modified financing receivable.

+ References

+ Details

Name:	us-gaap_FinancingReceivableModificationsPostModificationRecordedInvestment2
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Amount, before troubled debt restructuring, of financing receivable to be modified.

+ References

+ Details

Name:	us-gaap_FinancingReceivableModificationsPreModificationRecordedInvestment2
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Details

Name:	us-gaap_FinancialInstrumentPerformanceStatusAxis=us-gaap_NonperformingFinancingReceivableMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivablePortfolioSegmentAxis=obnk_RealEstatePortfolioSegmentMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=obnk_ConstructionLandandLandDevelopmentLoansMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=us-gaap_ResidentialRealEstateMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivablePortfolioSegmentAxis=us-gaap_CommercialPortfolioSegmentMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_LoanRestructuringModificationAxis=obnk_TermConcessionMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_LoanRestructuringModificationAxis=us-gaap_ContractualInterestRateReductionMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_LoanRestructuringModificationAxis=obnk_CombinationMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Loans - Pre-Modification Balances of TDR (Details) - Nonperforming Financial Instruments $ in Thousands	3 Months Ended	6 Months Ended
	Jun. 30, 2022 USD ($) loan	Jun. 30, 2022 USD ($) loan	Jun. 30, 2021 loan
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of Loans Restructured \| loan	3	5	0
Pre-Modification Recorded Balance	$ 4,546	$ 5,210
Total Modifications	$ 4,473	$ 5,137
Real estate
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of Loans Restructured \| loan		3
Pre-Modification Recorded Balance		$ 4,546
Total Modifications		$ 4,473
Real estate \| Construction/land/land development
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of Loans Restructured \| loan	2	2
Pre-Modification Recorded Balance	$ 850	$ 850
Total Modifications	$ 803	$ 803
Real estate \| Residential real estate
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of Loans Restructured \| loan	1	1
Pre-Modification Recorded Balance	$ 3,696	$ 3,696
Total Modifications	3,670	$ 3,670
Commercial and industrial
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of Loans Restructured \| loan		2
Pre-Modification Recorded Balance		$ 664
Total Modifications		664
Term Concessions
Financing Receivable, Troubled Debt Restructuring [Line Items]
Total Modifications	705	1,369
Term Concessions \| Real estate
Financing Receivable, Troubled Debt Restructuring [Line Items]
Total Modifications		705
Term Concessions \| Real estate \| Construction/land/land development
Financing Receivable, Troubled Debt Restructuring [Line Items]
Total Modifications	705	705
Term Concessions \| Real estate \| Residential real estate
Financing Receivable, Troubled Debt Restructuring [Line Items]
Total Modifications		0
Term Concessions \| Commercial and industrial
Financing Receivable, Troubled Debt Restructuring [Line Items]
Total Modifications		664
Interest Rate Concessions
Financing Receivable, Troubled Debt Restructuring [Line Items]
Total Modifications	3,670	3,670
Interest Rate Concessions \| Real estate
Financing Receivable, Troubled Debt Restructuring [Line Items]
Total Modifications		3,670
Interest Rate Concessions \| Real estate \| Construction/land/land development
Financing Receivable, Troubled Debt Restructuring [Line Items]
Total Modifications	0	0
Interest Rate Concessions \| Real estate \| Residential real estate
Financing Receivable, Troubled Debt Restructuring [Line Items]
Total Modifications	3,670	3,670
Interest Rate Concessions \| Commercial and industrial
Financing Receivable, Troubled Debt Restructuring [Line Items]
Total Modifications		0
Combination of Term and Rate Concessions
Financing Receivable, Troubled Debt Restructuring [Line Items]
Total Modifications	98	98
Combination of Term and Rate Concessions \| Real estate
Financing Receivable, Troubled Debt Restructuring [Line Items]
Total Modifications		98
Combination of Term and Rate Concessions \| Real estate \| Construction/land/land development
Financing Receivable, Troubled Debt Restructuring [Line Items]
Total Modifications	98	98
Combination of Term and Rate Concessions \| Real estate \| Residential real estate
Financing Receivable, Troubled Debt Restructuring [Line Items]
Total Modifications	$ 0	0
Combination of Term and Rate Concessions \| Commercial and industrial
Financing Receivable, Troubled Debt Restructuring [Line Items]
Total Modifications		$ 0