XML 56 R45.htm IDEA: XBRL DOCUMENT
v3.22.2.2

Loans and Allowance for Credit Losses on Loans - Major Classifications - Loan Concentrations (Details) | 9 Months Ended | 12 Months Ended
--- | --- | ---
Sep. 30, 2022 | Dec. 31, 2021
Real estate | Loan receivables | Customer Concentration Risk |  |
Loans |  |
Loans receivable as a percentage of total portfolio | 70.20% | 71.60%

X
- Definition Represents the percentage of total portfolio that is represented by a particular financial receivable category. + References No definition available. + Details
Name: | osbc_LoansAndLeasesReceivableAsPercentageOfAggregatePortfolio
Namespace Prefix: | osbc_
Data Type: | dtr-types:percentItemType
Balance Type: | na
Period Type: | duration

X
- 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 No definition available. + Details
Name: | us-gaap_AccountsNotesAndLoansReceivableLineItems
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Details
Name: | us-gaap_FinancingReceivablePortfolioSegmentAxis=osbc_RealEstatePortfolioSegmentMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_ConcentrationRiskByBenchmarkAxis=us-gaap_AccountsReceivableMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_ConcentrationRiskByTypeAxis=us-gaap_CustomerConcentrationRiskMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |