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v3.22.2.2

Fair Value Measurements (Details) - USD ($) | 9 Months Ended
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Sep. 30, 2022 | Sep. 30, 2021
Fair Value Measurements |  |
Fair value transfer assets , level 1 to level 2 | $ 0 | $ 0

X
- Definition Amount of transfers of assets measured on a recurring basis out of Level 1 of the fair value hierarchy into Level 2. + References No definition available. + Details
Name: | osbc_FairValueAssetsLevel1ToLevel2TransfersAmount1
Namespace Prefix: | osbc_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- References No definition available. + Details
Name: | us-gaap_FairValueDisclosuresAbstract
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration