Amortized cost excluding accrued interest, of financing receivable modified during period for debtor experiencing financial difficulty.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 310
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 42
-Subparagraph (a)(1)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481962/310-10-50-42

+ Details

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

- Definition

Percentage, excluding accrued interest, of financing receivable modified during period for debtor experiencing financial difficulty to total financing receivables.

+ References

+ Details

Name:	us-gaap_FinancingReceivableModificationToTotalFinancingReceivablesExcludingAccruedInterestPercent
Namespace Prefix:	us-gaap_
Data Type:	dtr-types:percentItemType
Balance Type:	na
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

Reference 1: http://fasb.org/us-gaap/role/ref/otherTransitionRef
-Topic 310
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 34
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481962/310-10-50-34

Reference 2: http://fasb.org/us-gaap/role/ref/otherTransitionRef
-Topic 310
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 33
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481962/310-10-50-33

Reference 3: http://www.xbrl.org/2003/role/exampleRef
-Topic 310
-SubTopic 10
-Name Accounting Standards Codification
-Section 55
-Paragraph 12A
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481933/310-10-55-12A

Reference 4: http://www.xbrl.org/2003/role/disclosureRef
-Topic 310
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 42
-Subparagraph (a)(2)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481962/310-10-50-42

Reference 5: http://www.xbrl.org/2003/role/disclosureRef
-Topic 310
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 42
-Subparagraph (a)(1)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481962/310-10-50-42

+ Details

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

- Definition

Percentage, after modification, of weighted-average interest rate of financing receivable for debtor experiencing financial difficulty.

+ References

Reference 1: http://www.xbrl.org/2003/role/exampleRef
-Topic 310
-SubTopic 10
-Name Accounting Standards Codification
-Section 55
-Paragraph 12A
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481933/310-10-55-12A

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 310
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 42
-Subparagraph (a)(2)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481962/310-10-50-42

+ Details

Name:	us-gaap_FinancingReceivableModifiedWeightedAverageInterestRateAfterModification
Namespace Prefix:	us-gaap_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Percentage, before modification, of weighted-average interest rate of financing receivable for debtor experiencing financial difficulty.

+ References

+ Details

Name:	us-gaap_FinancingReceivableModifiedWeightedAverageInterestRateBeforeModification
Namespace Prefix:	us-gaap_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Period of increase in weighted average maturity of financing receivable modified for debtor experiencing financial difficulty, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

+ References

+ Details

Name:	us-gaap_FinancingReceivableModifiedWeightedAverageTermIncreaseFromModification
Namespace Prefix:	us-gaap_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Details

Name:	us-gaap_LoanRestructuringModificationAxis=us-gaap_ExtendedMaturityMember
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_FinancingReceivablePortfolioSegmentAxis=us-gaap_CommercialPortfolioSegmentMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

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

- Details

Name:	us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=us-gaap_CommercialRealEstateMember
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_LoanRestructuringModificationAxis=us-gaap_ExtendedMaturityAndInterestRateReductionMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_LoanRestructuringModificationAxis=us-gaap_PaymentDeferralMember
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:

Loans - Troubled Debt Restructurings (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2024	Jun. 30, 2023	Jun. 30, 2024	Jun. 30, 2023
Term Extension
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amortized Cost	$ 16,574	$ 7,386	$ 22,046	$ 19,560
% of Loans	0.21%	0.10%	0.28%	0.26%
Term Extension \| Real estate
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amortized Cost	$ 3,067	$ 5,178	$ 3,745	$ 8,381
% of Loans	0.06%	0.10%	0.07%	0.16%
Term Extension \| Commercial and Industrial
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amortized Cost	$ 13,507	$ 2,208	$ 18,301	$ 11,179
% of Loans	0.65%	0.11%	0.88%	0.57%
Weighted average term extension (in months)	3 months 18 days	12 months 27 days	4 months 27 days	5 months 18 days
Term Extension \| Consumer
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amortized Cost	$ 0		$ 0
% of Loans	0.00%		0.00%
Weighted average term extension (in months)	5 months		5 months
Term Extension \| Commercial real estate \| Real estate
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amortized Cost	$ 268	$ 1,692	$ 268	$ 2,554
% of Loans	0.01%	0.07%	0.01%	0.11%
Weighted average term extension (in months)	3 months	12 months 21 days	3 months	11 months 27 days
Term Extension \| Construction/land/land development \| Real estate
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amortized Cost	$ 847	$ 1,747	$ 1,489	$ 4,088
% of Loans	0.08%	0.17%	0.15%	0.40%
Weighted average term extension (in months)	2 months 9 days	2 months 24 days	5 months	5 months 3 days
Term Extension \| Residential real estate \| Real estate
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amortized Cost	$ 1,952	$ 1,739	$ 1,988	$ 1,739
% of Loans	0.11%	0.11%	0.11%	0.11%
Weighted average term extension (in months)	3 months 6 days	5 months 9 days	3 months 9 days	5 months 9 days
Combination: Term Extension and Interest Rate Reduction
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amortized Cost	$ 138	$ 186	$ 138	$ 186
% of Loans	0.00%	0.00%	0.00%	0.00%
Combination: Term Extension and Interest Rate Reduction \| Real estate
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amortized Cost	$ 134	$ 0	$ 134	$ 0
% of Loans	0.00%	0.00%	0.00%	0.00%
Combination: Term Extension and Interest Rate Reduction \| Commercial and Industrial
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amortized Cost	$ 0	$ 186	$ 0	$ 186
% of Loans	0.00%	0.01%	0.00%	0.01%
Combination: Term Extension and Interest Rate Reduction \| Consumer
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amortized Cost	$ 4		$ 4
% of Loans	0.02%		0.02%
Combination: Term Extension and Interest Rate Reduction \| Commercial real estate \| Real estate
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amortized Cost	$ 0	$ 0	$ 0	$ 0
% of Loans	0.00%	0.00%	0.00%	0.00%
Combination: Term Extension and Interest Rate Reduction \| Construction/land/land development \| Real estate
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amortized Cost	$ 0	$ 0	$ 0	$ 0
% of Loans	0.00%	0.00%	0.00%	0.00%
Combination: Term Extension and Interest Rate Reduction \| Residential real estate \| Real estate
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amortized Cost	$ 134	$ 0	$ 134	$ 0
% of Loans	0.01%	0.00%	0.01%	0.00%
Other-Than-Insignificant Payment Delay
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amortized Cost			$ 35
% of Loans			0.00%
Other-Than-Insignificant Payment Delay \| Real estate
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amortized Cost			$ 0
% of Loans			0.00%
Other-Than-Insignificant Payment Delay \| Commercial and Industrial
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amortized Cost			$ 35
% of Loans			0.00%
Weighted average term extension (in months)			2 months
Other-Than-Insignificant Payment Delay \| Consumer
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amortized Cost			$ 0
% of Loans			0.00%
Other-Than-Insignificant Payment Delay \| Commercial real estate \| Real estate
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amortized Cost			$ 0
% of Loans			0.00%
Other-Than-Insignificant Payment Delay \| Construction/land/land development \| Real estate
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amortized Cost			$ 0
% of Loans			0.00%
Other-Than-Insignificant Payment Delay \| Residential real estate \| Real estate
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amortized Cost			$ 0
% of Loans			0.00%
Interest Rate Reduction \| Commercial and Industrial
Financing Receivable, Troubled Debt Restructuring [Line Items]
Weighted-average contractual interest rate before modification		9.00%		9.00%
Weighted-average contractual interest rate after modification		6.00%		6.00%
Interest Rate Reduction \| Consumer
Financing Receivable, Troubled Debt Restructuring [Line Items]
Weighted-average contractual interest rate before modification	9.50%		9.50%
Weighted-average contractual interest rate after modification	6.00%		6.00%
Interest Rate Reduction \| Residential real estate \| Real estate
Financing Receivable, Troubled Debt Restructuring [Line Items]
Weighted-average contractual interest rate before modification	9.00%		9.00%
Weighted-average contractual interest rate after modification	8.00%		8.00%