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Mortgage Banking - Narrative (Details) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2025	Sep. 30, 2024	Sep. 30, 2025	Sep. 30, 2024	Dec. 31, 2024
Mortgage Banking [Abstract]
Gain on sale of MSR asset	$ 0	$ 0	$ 0	$ 410,000
Mortgage servicing rights assets recognized or recorded during period			$ 0
Annual servicing fee income rate			0.25%
Reserve for mortgage loan servicing putback expenses	$ 103,000		$ 103,000		$ 103,000

X

- Definition

Gain (Loss) on Sale of Mortgage Servicing Rights

+ References

No definition available.

+ Details

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X

- Definition

Mortgage Loan Servicing Putback Expenses, Reserve

+ References

No definition available.

+ Details

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Namespace Prefix:	obnk_
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Balance Type:	credit
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X

- Definition

Servicing Fee Income, Rate

+ References

No definition available.

+ Details

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Namespace Prefix:	obnk_
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Balance Type:	na
Period Type:	duration

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- References

No definition available.

+ Details

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Namespace Prefix:	us-gaap_
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Balance Type:	na
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X

- Definition

The value of new servicing assets, subsequently measured at fair value, acquired or created during the current period through purchases or from transfers of financial assets.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 860
-SubTopic 50
-Name Accounting Standards Codification
-Section 50
-Paragraph 3
-Subparagraph (a)(2)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481229/860-50-50-3

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