Represents the percentage of total portfolio that is represented by a particular financial receivable category.

No definition available.

Name:	osbc_LoansAndLeasesReceivableAsPercentageOfAggregatePortfolio
Namespace Prefix:	osbc_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Amount of deferred interest and fee income, net of deferred costs.

+ References

No definition available.

+ Details

Name:	osbc_LoansAndLeasesReceivableDeferredIncomeExpenseNet
Namespace Prefix:	osbc_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Details

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

- Definition

Amount before allowance of loans and leases held in portfolio, including but not limited to, commercial and consumer loans. Includes deferred interest and fees, undisbursed portion of loan balance, unamortized costs and premiums and discounts from face amounts. 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 45

-Paragraph 2

-URI http://asc.fasb.org/extlink&oid=28367877&loc=d3e4428-111522

+ Details

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

- Definition

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 310

-SubTopic 10

-Section 45

-Paragraph 2

-URI http://asc.fasb.org/extlink&oid=28367877&loc=d3e4428-111522

+ Details

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

Loans - Major Classifications (Details) (USD $) In Thousands, unless otherwise specified													9 Months Ended	12 Months Ended
	Sep. 30, 2014	Dec. 31, 2013	Sep. 30, 2013	Sep. 30, 2014 Overdraft	Dec. 31, 2013 Overdraft	Sep. 30, 2014 Lease financing receivables	Dec. 31, 2013 Lease financing receivables	Sep. 30, 2014 Other	Dec. 31, 2013 Other	Sep. 30, 2014 Commercial	Dec. 31, 2013 Commercial	Sep. 30, 2013 Commercial	Sep. 30, 2014 Total real estate Loan receivables Customer concentration risk	Dec. 31, 2013 Total real estate Loan receivables Customer concentration risk	Sep. 30, 2014 Real estate - commercial	Dec. 31, 2013 Real estate - commercial	Sep. 30, 2013 Real estate - commercial	Sep. 30, 2014 Real estate - construction	Dec. 31, 2013 Real estate - construction	Sep. 30, 2013 Real estate - construction	Sep. 30, 2014 Real estate - residential	Dec. 31, 2013 Real estate - residential	Sep. 30, 2013 Real estate - residential	Sep. 30, 2014 Consumer	Dec. 31, 2013 Consumer	Sep. 30, 2013 Consumer
Loans
Total loans, gross	$ 1,140,274	$ 1,100,771		$ 1,198	$ 628	$ 8,398	$ 10,069	$ 12,757	$ 12,793	$ 106,592	$ 94,736				$ 600,649	$ 560,233		$ 41,936	$ 29,351		$ 365,602	$ 390,201		$ 3,142	$ 2,760
Net deferred loan fees	608	485
Total Loans	$ 1,140,882	$ 1,101,256	$ 1,077,640							$ 114,990	$ 104,805	$ 98,026			$ 600,649		$ 554,874	$ 41,936		$ 30,996	$ 365,602		$ 376,859	$ 3,142	$ 2,760	$ 2,570
Loans receivable as a percentage of total portfolio													88.40%	89.00%