Business Acquisition, Equity Interests Issued Or Issuable Number Of Shares Converted

No definition available.

Name:	obnk_BusinessAcquisitionEquityInterestsIssuedOrIssuableNumberOfSharesConverted
Namespace Prefix:	obnk_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	duration

- Definition

Share-Based Compensation Arrangement By Share-Based Payment Award, Award Performance Period

+ References

No definition available.

+ Details

Name:	obnk_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardPerformancePeriod
Namespace Prefix:	obnk_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Share-based Compensation Arrangement By Share-based Payment Award, Number Of Categories

+ References

No definition available.

+ Details

Name:	obnk_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfCategories
Namespace Prefix:	obnk_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

- Definition

Share-based Compensation Arrangement by Share-based Payment Award, Offering Period

+ References

No definition available.

+ Details

Name:	obnk_ShareBasedCompensationArrangementByShareBasedPaymentAwardOfferingPeriod
Namespace Prefix:	obnk_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Share-based Compensation Arrangement by Share-based Payment Award, Target Percentage

+ References

No definition available.

+ Details

Name:	obnk_ShareBasedCompensationArrangementByShareBasedPaymentAwardTargetPercentage
Namespace Prefix:	obnk_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Amount of expense for award under share-based payment arrangement. Excludes amount capitalized.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 718
-SubTopic 10
-Name Accounting Standards Codification
-Section S45
-Paragraph 1
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479983/718-10-S45-1

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 718
-SubTopic 10
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SAB Topic 14.F)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479830/718-10-S99-1

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Topic 718
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (h)(1)(i)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480429/718-10-50-2

+ Details

Name:	us-gaap_AllocatedShareBasedCompensationExpense
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

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 718
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (h)(1)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480429/718-10-50-2

+ Details

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

- Definition

Weighted-average period over which cost not yet recognized is expected to be recognized for award under share-based payment arrangement, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents reported fact of one year, five months, and thirteen days.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 718
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (i)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480429/718-10-50-2

+ Details

Name:	us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedPeriodForRecognition1
Namespace Prefix:	us-gaap_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Amount of cost to be recognized for nonvested award under share-based payment arrangement. Excludes share and unit options.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 718
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (i)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480429/718-10-50-2

+ Details

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

- Definition

Estimated period over which an employee is required to provide service in exchange for the equity-based payment award, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

+ References

Reference 1: http://www.xbrl.org/2003/role/exampleRef
-Topic 718
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (a)(1)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480429/718-10-50-2

+ Details

Name:	us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardRequisiteServicePeriod1
Namespace Prefix:	us-gaap_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Discount rate from fair value on purchase date that participants pay for shares.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480429/718-10-50-2

+ Details

Name:	us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardDiscountFromMarketPricePurchaseDate
Namespace Prefix:	us-gaap_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Number of shares authorized for issuance under share-based payment arrangement.

+ References

Reference 1: http://www.xbrl.org/2003/role/exampleRef
-Topic 718
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (a)(3)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480429/718-10-50-2

+ Details

Name:	us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAuthorized
Namespace Prefix:	us-gaap_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	instant

- Definition

The difference between the maximum number of shares (or other type of equity) authorized for issuance under the plan (including the effects of amendments and adjustments), and the sum of: 1) the number of shares (or other type of equity) already issued upon exercise of options or other equity-based awards under the plan; and 2) shares (or other type of equity) reserved for issuance on granting of outstanding awards, net of cancellations and forfeitures, if applicable.

+ References

+ Details

Name:	us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrant
Namespace Prefix:	us-gaap_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	instant

- Definition

Period from grant date that an equity-based award expires, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

+ References

Reference 1: http://www.xbrl.org/2003/role/exampleRef
-Topic 718
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (a)(2)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480429/718-10-50-2

+ Details

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

- Details

Name:	us-gaap_BusinessAcquisitionAxis=obnk_BTHMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_StatementEquityComponentsAxis=us-gaap_CommonStockMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_AwardTypeAxis=us-gaap_EmployeeStockMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_AwardTypeAxis=us-gaap_PhantomShareUnitsPSUsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_RangeAxis=srt_MinimumMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_RangeAxis=srt_MaximumMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_AwardTypeAxis=us-gaap_RestrictedStockUnitsRSUMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_AwardTypeAxis=us-gaap_RestrictedStockMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_AwardTypeAxis=us-gaap_EmployeeStockOptionMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_PlanNameAxis=obnk_A2012PlanAndTheOmnibusPlanMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_PlanNameAxis=obnk_OmnibusPlanMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_PlanNameAxis=obnk_A2012PlanMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Stock and Incentive Compensation Plans - Narrative (Details)		3 Months Ended		6 Months Ended
	Aug. 01, 2022 shares	Jun. 30, 2025 USD ($) shares	Jun. 30, 2024 USD ($) shares	Jun. 30, 2025 USD ($) category shares	Jun. 30, 2024 USD ($) shares	Apr. 30, 2024 shares
Share-based Payment Arrangement, Expensed and Capitalized, Amount [Line Items]
Stock compensation expense		$ 2,067,000	$ 1,688,000	$ 3,882,000	$ 3,767,000
BTH \| Common Stock
Share-based Payment Arrangement, Expensed and Capitalized, Amount [Line Items]
Stock converted (in shares) \| shares	611,676
Employee Stock
Share-based Payment Arrangement, Expensed and Capitalized, Amount [Line Items]
Maximum number of common stock available for issuance (in shares) \| shares		1,000,000		1,000,000
Shares available for issuance (in shares) \| shares		812,472	871,040	812,472	871,040
Stock repurchase program, discount percentage				15.00%
Offering period				1 year
Unrecognized compensation cost		$ 476,000		$ 476,000
Unrecognized compensation cost weighted average period for recognition				10 months 24 days
Stock compensation expense		131,000	$ 119,000	$ 244,000	$ 225,000
PSU
Share-based Payment Arrangement, Expensed and Capitalized, Amount [Line Items]
Unrecognized compensation cost		5,000,000.0		$ 5,000,000.0
Unrecognized compensation cost weighted average period for recognition				1 year 2 months 12 days
Target percentage				100.00%
Performance period (in years)				3 years
Expiration period				3 years
Number of categories \| category				2
Stock compensation expense		750,000	412,000	$ 1,289,000	1,327,000
PSU \| Minimum
Share-based Payment Arrangement, Expensed and Capitalized, Amount [Line Items]
Target percentage				0.00%
PSU \| Maximum
Share-based Payment Arrangement, Expensed and Capitalized, Amount [Line Items]
Target percentage				150.00%
RSUs
Share-based Payment Arrangement, Expensed and Capitalized, Amount [Line Items]
Unrecognized compensation cost		11,100,000		$ 11,100,000
Unrecognized compensation cost weighted average period for recognition				2 years 10 months 24 days
RSUs \| Minimum
Share-based Payment Arrangement, Expensed and Capitalized, Amount [Line Items]
Service period in which time-vested awards are earned				1 year
RSUs \| Maximum
Share-based Payment Arrangement, Expensed and Capitalized, Amount [Line Items]
Service period in which time-vested awards are earned				7 years
RSAs
Share-based Payment Arrangement, Expensed and Capitalized, Amount [Line Items]
Unrecognized compensation cost		439,000		$ 439,000
Unrecognized compensation cost weighted average period for recognition				9 months 18 days
RSAs \| Minimum
Share-based Payment Arrangement, Expensed and Capitalized, Amount [Line Items]
Service period in which time-vested awards are earned				1 year
RSAs \| Maximum
Share-based Payment Arrangement, Expensed and Capitalized, Amount [Line Items]
Service period in which time-vested awards are earned				7 years
Stock Options
Share-based Payment Arrangement, Expensed and Capitalized, Amount [Line Items]
Stock compensation expense		$ 0	$ 0	$ 0	$ 0
2012 Plan and the Omnibus Plan
Share-based Payment Arrangement, Expensed and Capitalized, Amount [Line Items]
Maximum number of common stock available for issuance (in shares) \| shares		1,375,000		1,375,000
Omnibus Plan
Share-based Payment Arrangement, Expensed and Capitalized, Amount [Line Items]
Maximum number of common stock available for issuance (in shares) \| shares		330,259		330,259
Shares available for issuance (in shares) \| shares						675,000
2012 Plan
Share-based Payment Arrangement, Expensed and Capitalized, Amount [Line Items]
Shares available for issuance (in shares) \| shares						0