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Document and Entity Information | Oct. 21, 2020
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Document and Entity Information [Abstract] |
Document Type | 8-K
Document Period End Date | Oct. 21, 2020
Entity Registrant Name | OLD SECOND BANCORP INC
Entity Incorporation, State or Country Code | DE
Entity File Number | 000-10537
Entity Tax Identification Number | 36-3143493
Entity Address, Address Line One | 37 South River Street
Entity Address, City or Town | Aurora
Entity Address, State or Province | IL
Entity Address, Postal Zip Code | 60507
City Area Code | 630
Local Phone Number | 892-0202
Written Communications | false
Soliciting Material | false
Pre-commencement Tender Offer | false
Pre-commencement Issuer Tender Offer | false
Title of 12(b) Security | Common Stock
Trading Symbol | OSBC
Security Exchange Name | NASDAQ
Entity Emerging Growth Company | false
Entity Central Index Key | 0000357173
Amendment Flag | false

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