XML 67 R51.htm IDEA: XBRL DOCUMENT
v3.6.0.2

Summary of Significant Accounting Policies - Premises and Equipment (Details) - USD ($) $ / shares in Units, $ in Millions | 12 Months Ended |  |
--- | --- | --- | ---
Dec. 31, 2016 | Jan. 17, 2017 | Dec. 31, 2015
Transfers and Servicing of Financial Assets |  |  |
Mortgage loans serviced for others | $ 668.2 |  | $ 638.2
Subsequent Events |  |  |
Cash dividend declared (per share) |  | $ 1.00 |
Buildings | Minimum |  |  |
Premises and equipment |  |  |
Useful lives | 25 years |  |
Buildings | Maximum |  |  |
Premises and equipment |  |  |
Useful lives | 40 years |  |
Building improvements | Minimum |  |  |
Premises and equipment |  |  |
Useful lives | 3 years |  |
Building improvements | Maximum |  |  |
Premises and equipment |  |  |
Useful lives | 15 years |  |
Furniture and equipment | Minimum |  |  |
Premises and equipment |  |  |
Useful lives | 3 years |  |
Furniture and equipment | Maximum |  |  |
Premises and equipment |  |  |
Useful lives | 10 years |  |

X
- Definition Fair value as of the balance sheet date of mortgage loans representing net future revenues from contractually specified servicing fees, late charges, and other ancillary revenues, in excess of future costs related to servicing arrangements. + References No definition available. + Details
Name: | osbc_MortgageLoansServicingAssetAtFairValueAmount
Namespace Prefix: | osbc_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition The per share amount of a dividend declared, but not paid, as of the financial reporting date. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 50 -Paragraph 3 -URI http://asc.fasb.org/extlink&oid=6367179&loc=d3e4304-108586 + Details
Name: | us-gaap_DividendsPayableAmountPerShare
Namespace Prefix: | us-gaap_
Data Type: | num:perShareItemType
Balance Type: | na
Period Type: | instant

X
- Definition Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table. + References No definition available. + Details
Name: | us-gaap_PropertyPlantAndEquipmentLineItems
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Definition Useful life of long lived, physical assets used in the normal conduct of business and not intended for resale, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days. Examples include, but not limited to, land, buildings, machinery and equipment, office equipment, furniture and fixtures, and computer equipment. + References No definition available. + Details
Name: | us-gaap_PropertyPlantAndEquipmentUsefulLife
Namespace Prefix: | us-gaap_
Data Type: | xbrli:durationItemType
Balance Type: | na
Period Type: | duration

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

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

X
- Details
Name: | us-gaap_PropertyPlantAndEquipmentByTypeAxis=us-gaap_BuildingMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_RangeAxis=us-gaap_MinimumMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_RangeAxis=us-gaap_MaximumMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_PropertyPlantAndEquipmentByTypeAxis=us-gaap_BuildingImprovementsMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_PropertyPlantAndEquipmentByTypeAxis=us-gaap_FurnitureAndFixturesMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |