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Summary of Significant Accounting Policies - Intangible Assets (Details) (USD $) | Dec. 31, 2014 | Dec. 31, 2013
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Core Deposit Intangible Assets |  |
Carrying value of the intangible asset |  | $ 1,177,000 us-gaap_FiniteLivedIntangibleAssetsNet
Income Taxes |  |
Valuation allowance | $ 0 osbc_DeferredTaxAssetsValuationAllowanceOnAvailableForSaleSecurities |

X
- Definition Amount of available for sale investment securities deferred tax assets for which it is more likely than not that a tax benefit will not be realized. + References No definition available. + Details
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- Details
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- Definition Amount after amortization of assets, excluding financial assets and goodwill, lacking physical substance with a finite life. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 350 -SubTopic 30 -Section 50 -Paragraph 2 -Subparagraph (a)(1) -URI http://asc.fasb.org/extlink&oid=26713463&loc=d3e16323-109275 + Details
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- Details
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