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Loans and Allowance for Credit Losses on Loans - TDR (Details)	3 Months Ended		9 Months Ended
	Sep. 30, 2022 loan	Sep. 30, 2021 USD ($)	Sep. 30, 2022 USD ($)	Sep. 30, 2021 USD ($)
Loans and Allowance for Credit Losses on Loans
Number of TDR loan modifications | loan	0
Loan modification activity		$ 0	$ 39,000	$ 0
TDR's defaulted
Pre-modification outstanding recorded investment during the period			$ 0	$ 0

X

- References

No definition available.

+ Details

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- Definition

Amount of financing receivable modified as troubled debt restructuring.

+ References

No definition available.

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Namespace Prefix:	osbc_
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- References

No definition available.

+ Details

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- Definition

Number of financing receivables that have been modified by troubled debt restructurings.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 33
-URI https://asc.fasb.org/extlink&oid=123577603&loc=SL6953676-111524

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- Definition

Amount of financing receivable modified as troubled debt restructuring within previous 12 months, with subsequent payment default.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 34
-Subparagraph (a)(2)
-URI https://asc.fasb.org/extlink&oid=123577603&loc=SL6953682-111524

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