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Regulatory & Capital Matters - Dividend Restrictions and Deferrals (Details) $ in Millions | 3 Months Ended
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Mar. 31, 2023 USD ($)
Dividend Restrictions and Deferrals |
Number of previous years retained profit considered for dividend payment | 2 years
Minimum capital requirements, minimum percentage required | 2.50%
Payments of dividends | $ 51.2

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- References No definition available. + Details
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Namespace Prefix: | osbc_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

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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. + References No definition available. + Details
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Namespace Prefix: | osbc_
Data Type: | xbrli:durationItemType
Balance Type: | na
Period Type: | duration

X
- 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. + References No definition available. + Details
Name: | osbc_TierOneCommonEquityCapitalDistributionLimitationMinimumRegulatoryCapitalPercentageNextTwelveMonths
Namespace Prefix: | osbc_
Data Type: | dtr-types:percentItemType
Balance Type: | na
Period Type: | duration

X
- Definition The amount of dividends that can be declared or paid without affecting the banking or savings institution's regulatory capital position. + References No definition available. + Details
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Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant