XML 50 R59.htm IDEA: XBRL DOCUMENT
v2.4.1.9

Regulatory & Capital Matters (Details) (USD $) In Millions, unless otherwise specified | 1 Months Ended |  |
--- | --- | --- | ---
Apr. 30, 2014 | Mar. 31, 2015 | Dec. 31, 2014
Regulatory & Capital Matters |  |  |
Tier 1 capital leverage ratio (as a percent) |  | 9.82%us-gaap_TierOneLeverageCapitalToAverageAssets | 9.93%us-gaap_TierOneLeverageCapitalToAverageAssets
Total capital ratio (as a percent) |  | 17.30%us-gaap_CapitalToRiskWeightedAssets | 17.68%us-gaap_CapitalToRiskWeightedAssets
Proceeds from issuance of common stock | $ 64.0 us-gaap_SaleOfStockConsiderationReceivedOnTransaction |  |
Old Second National Bank |  |  |
Regulatory & Capital Matters |  |  |
Tier 1 capital leverage ratio (as a percent) |  | 12.15%us-gaap_TierOneLeverageCapitalToAverageAssets / dei_LegalEntityAxis = us-gaap_SubsidiariesMember | 12.02%us-gaap_TierOneLeverageCapitalToAverageAssets / dei_LegalEntityAxis = us-gaap_SubsidiariesMember
Tier One leverage ratio, basis point increase (as a percent) |  | 0.13%osbc_IncreaseInTierOneLeverageCapital / dei_LegalEntityAxis = us-gaap_SubsidiariesMember |
Total capital ratio (as a percent) |  | 18.18%us-gaap_CapitalToRiskWeightedAssets / dei_LegalEntityAxis = us-gaap_SubsidiariesMember | 18.73%us-gaap_CapitalToRiskWeightedAssets / dei_LegalEntityAxis = us-gaap_SubsidiariesMember
Risk-based capital ratio, basis point increase (as a percent) |  | 0.55%osbc_IncreaseInCapitalToRiskWeightedAssetsRatio / dei_LegalEntityAxis = us-gaap_SubsidiariesMember |
Old Second National Bank | Minimum |  |  |
Regulatory & Capital Matters |  |  |
Tier 1 capital leverage ratio, board-designated threshold |  | 8.00%osbc_BoardDesignatedTierOneLeverageCapitalToAverageAssets / dei_LegalEntityAxis = us-gaap_SubsidiariesMember / us-gaap_RangeAxis = us-gaap_MinimumMember |
Total Capital Ratio, board-designated threshold (as a percent) |  | 12.00%osbc_BoardDesignatedCapitalToRiskWeightedAssets / dei_LegalEntityAxis = us-gaap_SubsidiariesMember / us-gaap_RangeAxis = us-gaap_MinimumMember |

X
- Definition Represents the board-designated threshold for Total Capital divided by risk weighted assets as defined in the regulations. + References No definition available. + Details
Name: | osbc_BoardDesignatedCapitalToRiskWeightedAssets
Namespace Prefix: | osbc_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | instant

X
- Definition Board-designated threshold for Tier 1 Leverage Capital divided by average assets as defined in the regulations. + References No definition available. + Details
Name: | osbc_BoardDesignatedTierOneLeverageCapitalToAverageAssets
Namespace Prefix: | osbc_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | instant

X
- Definition Represents the basis point increase in the risk-based capital ratio over prior period. + References No definition available. + Details
Name: | osbc_IncreaseInCapitalToRiskWeightedAssetsRatio
Namespace Prefix: | osbc_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | instant

X
- Definition Represents the basis point increase in the Tier One leverage capital over prior period. + References No definition available. + Details
Name: | osbc_IncreaseInTierOneLeverageCapital
Namespace Prefix: | osbc_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | instant

X
- Definition Total Capital divided by risk weighted assets as defined in the regulations. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 505 -Section 50 -Paragraph 1H -Subparagraph (c)(2) -URI http://asc.fasb.org/extlink&oid=35709795&loc=d3e65071-112826 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 505 -Section 50 -Paragraph 1 -Subparagraph (c)(1) -URI http://asc.fasb.org/extlink&oid=35709795&loc=SL5958568-112826 + Details
Name: | us-gaap_CapitalToRiskWeightedAssets
Namespace Prefix: | us-gaap_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | instant

X
- Details
Name: | us-gaap_ComplianceWithRegulatoryCapitalRequirementsUnderBankingRegulationsLineItems
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Definition Cash received on stock transaction after deduction of issuance costs. + References No definition available. + Details
Name: | us-gaap_SaleOfStockConsiderationReceivedOnTransaction
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition Tier 1 Leverage Capital divided by average assets as defined in the regulations. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 505 -Section 50 -Paragraph 1H -Subparagraph (c)(2) -URI http://asc.fasb.org/extlink&oid=35709795&loc=d3e65071-112826 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 505 -Section 50 -Paragraph 1 -Subparagraph (c)(1) -URI http://asc.fasb.org/extlink&oid=35709795&loc=SL5958568-112826 + Details
Name: | us-gaap_TierOneLeverageCapitalToAverageAssets
Namespace Prefix: | us-gaap_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | instant

X
- Details
Name: | dei_LegalEntityAxis=us-gaap_SubsidiariesMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |