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Loans - Credit Quality (Details) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2015	Dec. 31, 2014	Mar. 31, 2014
Loans by risk rating
Total Loans	$ 1,151,069us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome	$ 1,159,332us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome	$ 1,111,237us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome
Commercial
Loans by risk rating
Total Loans	122,892us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember	127,196us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember	107,548us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember
Real estate - commercial
Loans by risk rating
Total Loans	608,267us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialRealEstatePortfolioSegmentMember		579,297us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialRealEstatePortfolioSegmentMember
Real estate - commercial | Owner occupied general purpose
Loans by risk rating
Total Loans	135,504us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = osbc_CommercialRealEstateOwnerOccupiedGeneralPurposeLoanMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialRealEstatePortfolioSegmentMember	132,665us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = osbc_CommercialRealEstateOwnerOccupiedGeneralPurposeLoanMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialRealEstatePortfolioSegmentMember
Real estate - commercial | Owner occupied special purpose
Loans by risk rating
Total Loans	172,142us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = osbc_CommercialRealEstateOwnerOccupiedSpecialPurposeLoanMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialRealEstatePortfolioSegmentMember	169,315us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = osbc_CommercialRealEstateOwnerOccupiedSpecialPurposeLoanMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialRealEstatePortfolioSegmentMember
Real estate - commercial | Non-owner occupied general purpose
Loans by risk rating
Total Loans	151,783us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = osbc_CommercialRealEstateNonOwnerOccupiedGeneralPurposeLoanMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialRealEstatePortfolioSegmentMember	158,235us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = osbc_CommercialRealEstateNonOwnerOccupiedGeneralPurposeLoanMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialRealEstatePortfolioSegmentMember
Real estate - commercial | Non-owner occupied special purpose
Loans by risk rating
Total Loans	93,900us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = osbc_CommercialRealEstateNonOwnerOccupiedSpecialPurposeLoanMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialRealEstatePortfolioSegmentMember	88,477us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = osbc_CommercialRealEstateNonOwnerOccupiedSpecialPurposeLoanMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialRealEstatePortfolioSegmentMember
Real estate - commercial | Retail properties
Loans by risk rating
Total Loans	41,012us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = osbc_CommercialRealEstateRetailPropertiesLoanMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialRealEstatePortfolioSegmentMember	37,780us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = osbc_CommercialRealEstateRetailPropertiesLoanMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialRealEstatePortfolioSegmentMember
Real estate - commercial | Farm
Loans by risk rating
Total Loans	13,926us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = osbc_CommercialRealEstateFarmLoanMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialRealEstatePortfolioSegmentMember	14,157us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = osbc_CommercialRealEstateFarmLoanMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialRealEstatePortfolioSegmentMember
Real estate - construction
Loans by risk rating
Total Loans	39,430us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialRealEstateConstructionFinancingReceivableMember		32,016us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialRealEstateConstructionFinancingReceivableMember
Real estate - construction | Homebuilder
Loans by risk rating
Total Loans	2,660us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = osbc_ConstructionRealEstateHomebuilderLoanMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialRealEstateConstructionFinancingReceivableMember	3,204us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = osbc_ConstructionRealEstateHomebuilderLoanMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialRealEstateConstructionFinancingReceivableMember
Real estate - construction | Land
Loans by risk rating
Total Loans	2,463us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = osbc_ConstructionRealEstateLandLoanMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialRealEstateConstructionFinancingReceivableMember	1,658us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = osbc_ConstructionRealEstateLandLoanMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialRealEstateConstructionFinancingReceivableMember
Real estate - construction | Commercial speculative
Loans by risk rating
Total Loans	6,300us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = osbc_ConstructionRealEstateCommercialSpeculativeLoanMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialRealEstateConstructionFinancingReceivableMember	13,431us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = osbc_ConstructionRealEstateCommercialSpeculativeLoanMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialRealEstateConstructionFinancingReceivableMember
Real estate - construction | All other
Loans by risk rating
Total Loans	28,007us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = osbc_ConstructionRealEstateOtherReceivableMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialRealEstateConstructionFinancingReceivableMember	26,502us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = osbc_ConstructionRealEstateOtherReceivableMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialRealEstateConstructionFinancingReceivableMember
Real estate - residential
Loans by risk rating
Total Loans	363,967us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_ResidentialPortfolioSegmentMember		375,781us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_ResidentialPortfolioSegmentMember
Real estate - residential | Investor
Loans by risk rating
Total Loans	135,848us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = osbc_ResidentialInvestorLoanMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_ResidentialPortfolioSegmentMember	137,215us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = osbc_ResidentialInvestorLoanMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_ResidentialPortfolioSegmentMember
Real estate - residential | Owner occupied
Loans by risk rating
Total Loans	115,962us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = osbc_ResidentialOwnerOccupiedLoanMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_ResidentialPortfolioSegmentMember	116,428us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = osbc_ResidentialOwnerOccupiedLoanMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_ResidentialPortfolioSegmentMember
Real estate - residential | Revolving and junior liens
Loans by risk rating
Total Loans	112,157us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = osbc_ResidentialRevolvingAndJuniorLiensLoanMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_ResidentialPortfolioSegmentMember	116,548us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = osbc_ResidentialRevolvingAndJuniorLiensLoanMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_ResidentialPortfolioSegmentMember
Consumer
Loans by risk rating
Total Loans	3,495us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_ConsumerPortfolioSegmentMember	3,504us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_ConsumerPortfolioSegmentMember	2,837us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_ConsumerPortfolioSegmentMember
All other
Loans by risk rating
Total Loans	13,018us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_UnallocatedFinancingReceivablesMember	13,017us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_UnallocatedFinancingReceivablesMember	13,758us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_UnallocatedFinancingReceivablesMember
Pass
Loans by risk rating
Total Loans	1,088,175us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome / us-gaap_InternalCreditAssessmentAxis = us-gaap_PassMember	1,090,065us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome / us-gaap_InternalCreditAssessmentAxis = us-gaap_PassMember
Pass | Commercial
Loans by risk rating
Total Loans	111,647us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / us-gaap_InternalCreditAssessmentAxis = us-gaap_PassMember	118,845us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / us-gaap_InternalCreditAssessmentAxis = us-gaap_PassMember
Pass | Real estate - commercial | Owner occupied general purpose
Loans by risk rating
Total Loans	125,429us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = osbc_CommercialRealEstateOwnerOccupiedGeneralPurposeLoanMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialRealEstatePortfolioSegmentMember / us-gaap_InternalCreditAssessmentAxis = us-gaap_PassMember	124,936us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = osbc_CommercialRealEstateOwnerOccupiedGeneralPurposeLoanMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialRealEstatePortfolioSegmentMember / us-gaap_InternalCreditAssessmentAxis = us-gaap_PassMember
Pass | Real estate - commercial | Owner occupied special purpose
Loans by risk rating
Total Loans	161,825us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = osbc_CommercialRealEstateOwnerOccupiedSpecialPurposeLoanMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialRealEstatePortfolioSegmentMember / us-gaap_InternalCreditAssessmentAxis = us-gaap_PassMember	154,225us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = osbc_CommercialRealEstateOwnerOccupiedSpecialPurposeLoanMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialRealEstatePortfolioSegmentMember / us-gaap_InternalCreditAssessmentAxis = us-gaap_PassMember
Pass | Real estate - commercial | Non-owner occupied general purpose
Loans by risk rating
Total Loans	146,281us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = osbc_CommercialRealEstateNonOwnerOccupiedGeneralPurposeLoanMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialRealEstatePortfolioSegmentMember / us-gaap_InternalCreditAssessmentAxis = us-gaap_PassMember	148,212us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = osbc_CommercialRealEstateNonOwnerOccupiedGeneralPurposeLoanMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialRealEstatePortfolioSegmentMember / us-gaap_InternalCreditAssessmentAxis = us-gaap_PassMember
Pass | Real estate - commercial | Non-owner occupied special purpose
Loans by risk rating
Total Loans	88,655us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = osbc_CommercialRealEstateNonOwnerOccupiedSpecialPurposeLoanMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialRealEstatePortfolioSegmentMember / us-gaap_InternalCreditAssessmentAxis = us-gaap_PassMember	78,957us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = osbc_CommercialRealEstateNonOwnerOccupiedSpecialPurposeLoanMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialRealEstatePortfolioSegmentMember / us-gaap_InternalCreditAssessmentAxis = us-gaap_PassMember
Pass | Real estate - commercial | Retail properties
Loans by risk rating
Total Loans	38,501us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = osbc_CommercialRealEstateRetailPropertiesLoanMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialRealEstatePortfolioSegmentMember / us-gaap_InternalCreditAssessmentAxis = us-gaap_PassMember	36,779us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = osbc_CommercialRealEstateRetailPropertiesLoanMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialRealEstatePortfolioSegmentMember / us-gaap_InternalCreditAssessmentAxis = us-gaap_PassMember
Pass | Real estate - commercial | Farm
Loans by risk rating
Total Loans	12,027us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = osbc_CommercialRealEstateFarmLoanMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialRealEstatePortfolioSegmentMember / us-gaap_InternalCreditAssessmentAxis = us-gaap_PassMember	14,157us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = osbc_CommercialRealEstateFarmLoanMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialRealEstatePortfolioSegmentMember / us-gaap_InternalCreditAssessmentAxis = us-gaap_PassMember
Pass | Real estate - construction | Homebuilder
Loans by risk rating
Total Loans	2,660us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = osbc_ConstructionRealEstateHomebuilderLoanMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialRealEstateConstructionFinancingReceivableMember / us-gaap_InternalCreditAssessmentAxis = us-gaap_PassMember	3,204us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = osbc_ConstructionRealEstateHomebuilderLoanMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialRealEstateConstructionFinancingReceivableMember / us-gaap_InternalCreditAssessmentAxis = us-gaap_PassMember
Pass | Real estate - construction | Land
Loans by risk rating
Total Loans	2,463us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = osbc_ConstructionRealEstateLandLoanMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialRealEstateConstructionFinancingReceivableMember / us-gaap_InternalCreditAssessmentAxis = us-gaap_PassMember	1,658us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = osbc_ConstructionRealEstateLandLoanMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialRealEstateConstructionFinancingReceivableMember / us-gaap_InternalCreditAssessmentAxis = us-gaap_PassMember
Pass | Real estate - construction | Commercial speculative
Loans by risk rating
Total Loans	2,828us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = osbc_ConstructionRealEstateCommercialSpeculativeLoanMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialRealEstateConstructionFinancingReceivableMember / us-gaap_InternalCreditAssessmentAxis = us-gaap_PassMember	9,947us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = osbc_ConstructionRealEstateCommercialSpeculativeLoanMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialRealEstateConstructionFinancingReceivableMember / us-gaap_InternalCreditAssessmentAxis = us-gaap_PassMember
Pass | Real estate - construction | All other
Loans by risk rating
Total Loans	27,506us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = osbc_ConstructionRealEstateOtherReceivableMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialRealEstateConstructionFinancingReceivableMember / us-gaap_InternalCreditAssessmentAxis = us-gaap_PassMember	25,941us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = osbc_ConstructionRealEstateOtherReceivableMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialRealEstateConstructionFinancingReceivableMember / us-gaap_InternalCreditAssessmentAxis = us-gaap_PassMember
Pass | Real estate - residential | Investor
Loans by risk rating
Total Loans	134,673us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = osbc_ResidentialInvestorLoanMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_ResidentialPortfolioSegmentMember / us-gaap_InternalCreditAssessmentAxis = us-gaap_PassMember	134,952us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = osbc_ResidentialInvestorLoanMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_ResidentialPortfolioSegmentMember / us-gaap_InternalCreditAssessmentAxis = us-gaap_PassMember
Pass | Real estate - residential | Owner occupied
Loans by risk rating
Total Loans	108,433us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = osbc_ResidentialOwnerOccupiedLoanMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_ResidentialPortfolioSegmentMember / us-gaap_InternalCreditAssessmentAxis = us-gaap_PassMember	109,085us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = osbc_ResidentialOwnerOccupiedLoanMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_ResidentialPortfolioSegmentMember / us-gaap_InternalCreditAssessmentAxis = us-gaap_PassMember
Pass | Real estate - residential | Revolving and junior liens
Loans by risk rating
Total Loans	108,735us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = osbc_ResidentialRevolvingAndJuniorLiensLoanMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_ResidentialPortfolioSegmentMember / us-gaap_InternalCreditAssessmentAxis = us-gaap_PassMember	112,647us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = osbc_ResidentialRevolvingAndJuniorLiensLoanMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_ResidentialPortfolioSegmentMember / us-gaap_InternalCreditAssessmentAxis = us-gaap_PassMember
Pass | Consumer
Loans by risk rating
Total Loans	3,494us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_ConsumerPortfolioSegmentMember / us-gaap_InternalCreditAssessmentAxis = us-gaap_PassMember	3,503us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_ConsumerPortfolioSegmentMember / us-gaap_InternalCreditAssessmentAxis = us-gaap_PassMember
Pass | All other
Loans by risk rating
Total Loans	13,018us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_UnallocatedFinancingReceivablesMember / us-gaap_InternalCreditAssessmentAxis = us-gaap_PassMember	13,017us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_UnallocatedFinancingReceivablesMember / us-gaap_InternalCreditAssessmentAxis = us-gaap_PassMember
Special Mention
Loans by risk rating
Total Loans	26,473us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome / us-gaap_InternalCreditAssessmentAxis = us-gaap_SpecialMentionMember	28,329us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome / us-gaap_InternalCreditAssessmentAxis = us-gaap_SpecialMentionMember
Special Mention | Commercial
Loans by risk rating
Total Loans	6,309us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / us-gaap_InternalCreditAssessmentAxis = us-gaap_SpecialMentionMember	3,948us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / us-gaap_InternalCreditAssessmentAxis = us-gaap_SpecialMentionMember
Special Mention | Real estate - commercial | Owner occupied general purpose
Loans by risk rating
Total Loans	3,123us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = osbc_CommercialRealEstateOwnerOccupiedGeneralPurposeLoanMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialRealEstatePortfolioSegmentMember / us-gaap_InternalCreditAssessmentAxis = us-gaap_SpecialMentionMember	253us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = osbc_CommercialRealEstateOwnerOccupiedGeneralPurposeLoanMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialRealEstatePortfolioSegmentMember / us-gaap_InternalCreditAssessmentAxis = us-gaap_SpecialMentionMember
Special Mention | Real estate - commercial | Owner occupied special purpose
Loans by risk rating
Total Loans	6,894us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = osbc_CommercialRealEstateOwnerOccupiedSpecialPurposeLoanMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialRealEstatePortfolioSegmentMember / us-gaap_InternalCreditAssessmentAxis = us-gaap_SpecialMentionMember	11,607us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = osbc_CommercialRealEstateOwnerOccupiedSpecialPurposeLoanMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialRealEstatePortfolioSegmentMember / us-gaap_InternalCreditAssessmentAxis = us-gaap_SpecialMentionMember
Special Mention | Real estate - commercial | Non-owner occupied general purpose
Loans by risk rating
Total Loans	2,872us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = osbc_CommercialRealEstateNonOwnerOccupiedGeneralPurposeLoanMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialRealEstatePortfolioSegmentMember / us-gaap_InternalCreditAssessmentAxis = us-gaap_SpecialMentionMember	3,235us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = osbc_CommercialRealEstateNonOwnerOccupiedGeneralPurposeLoanMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialRealEstatePortfolioSegmentMember / us-gaap_InternalCreditAssessmentAxis = us-gaap_SpecialMentionMember
Special Mention | Real estate - commercial | Non-owner occupied special purpose
Loans by risk rating
Total Loans	4,047us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = osbc_CommercialRealEstateNonOwnerOccupiedSpecialPurposeLoanMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialRealEstatePortfolioSegmentMember / us-gaap_InternalCreditAssessmentAxis = us-gaap_SpecialMentionMember	8,097us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = osbc_CommercialRealEstateNonOwnerOccupiedSpecialPurposeLoanMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialRealEstatePortfolioSegmentMember / us-gaap_InternalCreditAssessmentAxis = us-gaap_SpecialMentionMember
Special Mention | Real estate - commercial | Retail properties
Loans by risk rating
Total Loans	2,511us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = osbc_CommercialRealEstateRetailPropertiesLoanMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialRealEstatePortfolioSegmentMember / us-gaap_InternalCreditAssessmentAxis = us-gaap_SpecialMentionMember	1,001us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = osbc_CommercialRealEstateRetailPropertiesLoanMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialRealEstatePortfolioSegmentMember / us-gaap_InternalCreditAssessmentAxis = us-gaap_SpecialMentionMember
Special Mention | Real estate - commercial | Farm
Loans by risk rating
Total Loans	529us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = osbc_CommercialRealEstateFarmLoanMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialRealEstatePortfolioSegmentMember / us-gaap_InternalCreditAssessmentAxis = us-gaap_SpecialMentionMember
Special Mention | Real estate - residential | Revolving and junior liens
Loans by risk rating
Total Loans	188us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = osbc_ResidentialRevolvingAndJuniorLiensLoanMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_ResidentialPortfolioSegmentMember / us-gaap_InternalCreditAssessmentAxis = us-gaap_SpecialMentionMember	188us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = osbc_ResidentialRevolvingAndJuniorLiensLoanMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_ResidentialPortfolioSegmentMember / us-gaap_InternalCreditAssessmentAxis = us-gaap_SpecialMentionMember
Substandard
Loans by risk rating
Total Loans	36,421us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome / us-gaap_InternalCreditAssessmentAxis = us-gaap_SubstandardMember	40,938us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome / us-gaap_InternalCreditAssessmentAxis = us-gaap_SubstandardMember
Substandard | Commercial
Loans by risk rating
Total Loans	4,936us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / us-gaap_InternalCreditAssessmentAxis = us-gaap_SubstandardMember	4,403us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember / us-gaap_InternalCreditAssessmentAxis = us-gaap_SubstandardMember
Substandard | Real estate - commercial | Owner occupied general purpose
Loans by risk rating
Total Loans	6,952us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = osbc_CommercialRealEstateOwnerOccupiedGeneralPurposeLoanMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialRealEstatePortfolioSegmentMember / us-gaap_InternalCreditAssessmentAxis = us-gaap_SubstandardMember	7,476us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = osbc_CommercialRealEstateOwnerOccupiedGeneralPurposeLoanMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialRealEstatePortfolioSegmentMember / us-gaap_InternalCreditAssessmentAxis = us-gaap_SubstandardMember
Substandard | Real estate - commercial | Owner occupied special purpose
Loans by risk rating
Total Loans	3,423us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = osbc_CommercialRealEstateOwnerOccupiedSpecialPurposeLoanMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialRealEstatePortfolioSegmentMember / us-gaap_InternalCreditAssessmentAxis = us-gaap_SubstandardMember	3,483us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = osbc_CommercialRealEstateOwnerOccupiedSpecialPurposeLoanMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialRealEstatePortfolioSegmentMember / us-gaap_InternalCreditAssessmentAxis = us-gaap_SubstandardMember
Substandard | Real estate - commercial | Non-owner occupied general purpose
Loans by risk rating
Total Loans	2,630us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = osbc_CommercialRealEstateNonOwnerOccupiedGeneralPurposeLoanMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialRealEstatePortfolioSegmentMember / us-gaap_InternalCreditAssessmentAxis = us-gaap_SubstandardMember	6,788us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = osbc_CommercialRealEstateNonOwnerOccupiedGeneralPurposeLoanMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialRealEstatePortfolioSegmentMember / us-gaap_InternalCreditAssessmentAxis = us-gaap_SubstandardMember
Substandard | Real estate - commercial | Non-owner occupied special purpose
Loans by risk rating
Total Loans	1,198us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = osbc_CommercialRealEstateNonOwnerOccupiedSpecialPurposeLoanMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialRealEstatePortfolioSegmentMember / us-gaap_InternalCreditAssessmentAxis = us-gaap_SubstandardMember	1,423us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = osbc_CommercialRealEstateNonOwnerOccupiedSpecialPurposeLoanMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialRealEstatePortfolioSegmentMember / us-gaap_InternalCreditAssessmentAxis = us-gaap_SubstandardMember
Substandard | Real estate - commercial | Farm
Loans by risk rating
Total Loans	1,370us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = osbc_CommercialRealEstateFarmLoanMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialRealEstatePortfolioSegmentMember / us-gaap_InternalCreditAssessmentAxis = us-gaap_SubstandardMember
Substandard | Real estate - construction | Commercial speculative
Loans by risk rating
Total Loans	3,472us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = osbc_ConstructionRealEstateCommercialSpeculativeLoanMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialRealEstateConstructionFinancingReceivableMember / us-gaap_InternalCreditAssessmentAxis = us-gaap_SubstandardMember	3,484us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = osbc_ConstructionRealEstateCommercialSpeculativeLoanMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialRealEstateConstructionFinancingReceivableMember / us-gaap_InternalCreditAssessmentAxis = us-gaap_SubstandardMember
Substandard | Real estate - construction | All other
Loans by risk rating
Total Loans	501us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = osbc_ConstructionRealEstateOtherReceivableMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialRealEstateConstructionFinancingReceivableMember / us-gaap_InternalCreditAssessmentAxis = us-gaap_SubstandardMember	561us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = osbc_ConstructionRealEstateOtherReceivableMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialRealEstateConstructionFinancingReceivableMember / us-gaap_InternalCreditAssessmentAxis = us-gaap_SubstandardMember
Substandard | Real estate - residential | Investor
Loans by risk rating
Total Loans	1,175us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = osbc_ResidentialInvestorLoanMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_ResidentialPortfolioSegmentMember / us-gaap_InternalCreditAssessmentAxis = us-gaap_SubstandardMember	2,263us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = osbc_ResidentialInvestorLoanMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_ResidentialPortfolioSegmentMember / us-gaap_InternalCreditAssessmentAxis = us-gaap_SubstandardMember
Substandard | Real estate - residential | Owner occupied
Loans by risk rating
Total Loans	7,529us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = osbc_ResidentialOwnerOccupiedLoanMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_ResidentialPortfolioSegmentMember / us-gaap_InternalCreditAssessmentAxis = us-gaap_SubstandardMember	7,343us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = osbc_ResidentialOwnerOccupiedLoanMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_ResidentialPortfolioSegmentMember / us-gaap_InternalCreditAssessmentAxis = us-gaap_SubstandardMember
Substandard | Real estate - residential | Revolving and junior liens
Loans by risk rating
Total Loans	3,234us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = osbc_ResidentialRevolvingAndJuniorLiensLoanMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_ResidentialPortfolioSegmentMember / us-gaap_InternalCreditAssessmentAxis = us-gaap_SubstandardMember	3,713us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = osbc_ResidentialRevolvingAndJuniorLiensLoanMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_ResidentialPortfolioSegmentMember / us-gaap_InternalCreditAssessmentAxis = us-gaap_SubstandardMember
Substandard | Consumer
Loans by risk rating
Total Loans	$ 1us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_ConsumerPortfolioSegmentMember / us-gaap_InternalCreditAssessmentAxis = us-gaap_SubstandardMember	$ 1us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_ConsumerPortfolioSegmentMember / us-gaap_InternalCreditAssessmentAxis = us-gaap_SubstandardMember

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Amount before allowance and after deduction of deferred interest and fees, unamortized costs and premiums and discounts from face amounts, of loans and leases held in portfolio, including but not limited to, commercial and consumer loans. Excludes loans and leases covered under loss sharing agreements.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 310

-SubTopic 10

-Section 50

-Paragraph 4

-URI http://asc.fasb.org/extlink&oid=35738203&loc=d3e5074-111524



Reference 2: http://www.xbrl.org/2003/role/presentationRef

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-Name Accounting Standards Codification

-Topic 310

-SubTopic 10

-Section 45

-Paragraph 2

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