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Regulatory & Capital Matters - Dividend Restrictions and Deferrals (Details) $ in Millions	9 Months Ended
	Sep. 30, 2025 USD ($)
Dividend Restrictions and Deferrals
Number of previous years retained profit considered for dividend payment	2 years
Payments of dividends	$ 96.6
Minimum capital requirements, minimum percentage required	2.50%

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- References

No definition available.

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- Definition

Represents the number of previous years retained profits combined with the current years profits used to determine the amount of dividends that may be paid in any calendar year.

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No definition available.

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- Definition

The minimum percentage of Tier 1 Common Capital required to be maintained in the next fiscal year following the latest fiscal year to prevent capital distribution limitations under regulatory capital rules.

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No definition available.

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Namespace Prefix:	osbc_
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- Definition

The amount of dividends that can be declared or paid without affecting the banking or savings institution's regulatory capital position.

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No definition available.

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