XML 87 R75.htm IDEA: XBRL DOCUMENT v3.25.3

Derivatives, Hedging Activities and Financial Instruments with Off-Balance Sheet Risk (Details)	9 Months Ended	12 Months Ended
	Sep. 30, 2025 USD ($) item	Dec. 31, 2024 USD ($) item
Derivatives, Hedging Activities and Financial Instruments with Off-Balance Sheet Risk
Amount to be reclassified as an increase to interest expense during the next twelve months	$ 274,000
Two financial institutions
Derivatives, Hedging Activities and Financial Instruments with Off-Balance Sheet Risk
Cash collateral pledged with financial institutions, dollars	$ 940,000	$ 2,300,000
Number of financial institutions in which cash collateral pledged | item	2	2
Interest Rate Swap
Derivatives, Hedging Activities and Financial Instruments with Off-Balance Sheet Risk
Cash collateral pledged with financial institutions, dollars	$ 3,400,000	$ 5,200,000
Number of financial institutions in which cash collateral pledged | item	1	1
Investment securities pledged with financial institutions, dollars	$ 0	$ 0
Designated as Hedging Instrument
Derivatives, Hedging Activities and Financial Instruments with Off-Balance Sheet Risk
Derivative assets designated as hedging instruments, fair value	2,880,000	3,823,000
Derivative liabilities designated as hedging instruments, fair value		1,512,000
Designated as Hedging Instrument | Interest Rate Products | Cash flow hedge of junior subordinated debentures and was executed to pay fixed and receive variable rate cash flows
Derivatives, Hedging Activities and Financial Instruments with Off-Balance Sheet Risk
Notional amount	25,800,000	25,800,000
Designated as Hedging Instrument | Interest Rate Products | OSBC Affiliates
Derivatives, Hedging Activities and Financial Instruments with Off-Balance Sheet Risk
Notional amount	$ 25,774,000	$ 325,774,000
Derivative, number of transactions | item	1	5
Derivative assets designated as hedging instruments, fair value	$ 2,880,000	$ 3,823,000
Derivative liabilities designated as hedging instruments, fair value		1,512,000
Designated as Hedging Instrument | Interest Rate Swap | Cash flow hedges of certain variable rate commercial and commercial real estate loan pools
Derivatives, Hedging Activities and Financial Instruments with Off-Balance Sheet Risk
Notional amount	0	300,000,000
Not Designated as Hedging Instrument
Derivatives, Hedging Activities and Financial Instruments with Off-Balance Sheet Risk
Derivative assets designated as hedging instruments, fair value	1,470,000	1,758,000
Derivative liabilities designated as hedging instruments, fair value	1,388,000	1,680,000
Not Designated as Hedging Instrument | Interest Rate Products | Commercial Loan Customers
Derivatives, Hedging Activities and Financial Instruments with Off-Balance Sheet Risk
Notional amount	$ 126,623,000	$ 154,137,000
Derivative, number of transactions | item	13	13
Derivative assets designated as hedging instruments, fair value	$ 1,369,000	$ 1,675,000
Derivative liabilities designated as hedging instruments, fair value	1,369,000	1,675,000
Not Designated as Hedging Instrument | Interest Rate Swap
Derivatives, Hedging Activities and Financial Instruments with Off-Balance Sheet Risk
Notional amount	126,600,000	121,200,000
Not Designated as Hedging Instrument | Interest rate cap
Derivatives, Hedging Activities and Financial Instruments with Off-Balance Sheet Risk
Notional amount		32,900,000
Not Designated as Hedging Instrument | Commitments.
Derivatives, Hedging Activities and Financial Instruments with Off-Balance Sheet Risk
Notional amount	20,500,000	8,700,000
Not Designated as Hedging Instrument | Interest Rate Lock Commitments and Forward Contracts.
Derivatives, Hedging Activities and Financial Instruments with Off-Balance Sheet Risk
Notional amount	$ 20,547,000	$ 8,667,000
Derivative, number of transactions | item	60	30
Derivative assets designated as hedging instruments, fair value	$ 69,000	$ 55,000
Not Designated as Hedging Instrument | Other Contracts
Derivatives, Hedging Activities and Financial Instruments with Off-Balance Sheet Risk
Notional amount	$ 69,397,000	$ 58,259,000
Derivative, number of transactions | item	6	5
Derivative assets designated as hedging instruments, fair value	$ 32,000	$ 28,000
Derivative liabilities designated as hedging instruments, fair value	$ 19,000	$ 5,000

X

- Definition

The estimated net amount of unrealized losses on interest rate cash flow hedges as of the balance sheet date expected to be reclassified to earnings within the next twelve months.

+ References

No definition available.

+ Details

Name:	osbc_InterestRateCashFlowHedgeLossToBeReclassifiedDuringNext12MonthsNet
Namespace Prefix:	osbc_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

X

- Definition

Represents the number of financial institutions in which cash collateral pledged.

+ References

No definition available.

+ Details

Name:	osbc_NumberOfFinancialInstitutionsInWhichCashCollateralPledged
Namespace Prefix:	osbc_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

X

- Definition

Carrying amount as of the balance sheet date of cash collateral held for borrowed securities, for which the cash is restricted as to withdrawal or usage.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Topic 942
-SubTopic 210
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03(1))
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147478546/942-210-S99-1

Reference 2: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 944
-SubTopic 210
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-03(a)(2))
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147478777/944-210-S99-1

+ Details

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

X

- Definition

Fair value of all asset derivatives designated as cash flow hedging instruments.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Topic 815
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 4B
-Subparagraph (c)(1)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480434/815-10-50-4B

+ Details

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

X

- Definition

Fair value of all liability derivatives designated as cash flow hedging instruments.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Topic 815
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 4B
-Subparagraph (c)(1)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480434/815-10-50-4B

+ Details

Name:	us-gaap_CashFlowHedgeDerivativeInstrumentLiabilitiesAtFairValue
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

X

- Definition

Amount, after allowance for credit loss, of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), investment in debt security measured at amortized cost (held-to-maturity), and investment in debt security measured at fair value with change in fair value recognized in net income (trading).

+ References

Reference 1: http://www.xbrl.org/2003/role/exampleRef
-Topic 944
-SubTopic 80
-Name Accounting Standards Codification
-Section 55
-Paragraph 14
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480078/944-80-55-14

Reference 2: http://www.xbrl.org/2003/role/exampleRef
-Topic 944
-SubTopic 80
-Name Accounting Standards Codification
-Section 55
-Paragraph 9
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480078/944-80-55-9

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Topic 944
-SubTopic 210
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-03(a)(1)(a))
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147478777/944-210-S99-1

Reference 4: http://www.xbrl.org/2003/role/disclosureRef
-Topic 320
-SubTopic 10
-Name Accounting Standards Codification
-Section 45
-Paragraph 1
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481830/320-10-45-1

Reference 5: http://www.xbrl.org/2003/role/disclosureRef
-Topic 944
-SubTopic 210
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-03(a)(1)(6))
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147478777/944-210-S99-1

+ Details

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

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

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 815
-SubTopic 40
-Name Accounting Standards Codification
-Section 50
-Paragraph 5
-Subparagraph (f)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480237/815-40-50-5

+ Details

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

X

- Definition

Nominal or face amount used to calculate payment on derivative.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 815
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 1B
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480434/815-10-50-1B

Reference 2: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 815
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 1A
-Subparagraph (d)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480434/815-10-50-1A

+ Details

Name:	us-gaap_DerivativeNotionalAmount
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	na
Period Type:	instant

X

- Definition

The number of derivative instruments of a particular group held by the entity.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 946
-SubTopic 210
-Name Accounting Standards Codification
-Section 50
-Paragraph 6
-Subparagraph (e)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147478795/946-210-50-6

Reference 2: http://www.xbrl.org/2003/role/exampleRef
-Topic 946
-SubTopic 210
-Name Accounting Standards Codification
-Section 55
-Paragraph 1
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147477439/946-210-55-1

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Topic 946
-SubTopic 320
-Name Accounting Standards Codification
-Section S99
-Paragraph 5
-Subparagraph (SX 210.12-13(Column A)(Footnote 3))
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147477271/946-320-S99-5

Reference 4: http://www.xbrl.org/2003/role/disclosureRef
-Topic 946
-SubTopic 320
-Name Accounting Standards Codification
-Section S99
-Paragraph 5
-Subparagraph (SX 210.12-13(Column C))
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147477271/946-320-S99-5

Reference 5: http://www.xbrl.org/2003/role/disclosureRef
-Topic 946
-SubTopic 320
-Name Accounting Standards Codification
-Section S99
-Paragraph 5A
-Subparagraph (SX 210.12-13A(Column B))
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147477271/946-320-S99-5A

Reference 6: http://fasb.org/us-gaap/role/ref/legacyRef
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 1B
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480434/815-10-50-1B

Reference 7: http://fasb.org/us-gaap/role/ref/legacyRef
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 1A
-Subparagraph (d)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480434/815-10-50-1A

+ Details

Name:	us-gaap_DerivativeNumberOfInstrumentsHeld
Namespace Prefix:	us-gaap_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant

X

- Details

Name:	srt_CounterpartyNameAxis=osbc_TwoFinancialInstitutionsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_DerivativeInstrumentRiskAxis=us-gaap_InterestRateSwapMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_HedgingDesignationAxis=us-gaap_DesignatedAsHedgingInstrumentMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_DerivativeInstrumentRiskAxis=us-gaap_InterestRateContractMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipAxis=osbc_CashFlowHedgeOfJuniorSubordinatedDebenturesAndWasExecutedToPayFixedAndReceiveVariableRateCashFlowsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	srt_CounterpartyNameAxis=osbc_OsbcAffiliatesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipAxis=osbc_CashFlowHedgesOfCertainVariableRateCommercialAndCommercialRealEstateLoanPoolsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_HedgingDesignationAxis=us-gaap_NondesignatedMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	srt_CounterpartyNameAxis=osbc_CommercialLoanCustomersMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_DerivativeInstrumentRiskAxis=us-gaap_InterestRateCapMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_DerivativeInstrumentRiskAxis=osbc_DerivativeCommitmentsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_DerivativeInstrumentRiskAxis=osbc_InterestRateLockCommitmentsAndForwardContractsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_DerivativeInstrumentRiskAxis=us-gaap_OtherContractMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: