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Equity Compensation Plans (Details) (USD $) | 12 Months Ended
--- | ---
Dec. 31, 2014 | Dec. 31, 2013 | Dec. 31, 2012
Equity Compensation Plans |  |  |
Total compensation cost | $ 295,000 us-gaap_AllocatedShareBasedCompensationExpense | $ 167,000 us-gaap_AllocatedShareBasedCompensationExpense | $ 291,000 us-gaap_AllocatedShareBasedCompensationExpense
Shares |  |  |
Canceled (in shares) | (7,000)us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsForfeituresInPeriod |  |
Weighted Average Exercise Price |  |  |
Canceled (in dollars per share) | $ 32.59 us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsForfeituresInPeriodWeightedAverageExercisePrice |  |
Weighted Average Grant Date Fair Value |  |  |
Gain on Recapture of Restricted Stock |  | 612,000 osbc_GainOnRecaptureOfRestrictedStock |
2014 Plan |  |  |
Equity Compensation Plans |  |  |
Number of shares authorized | 375,000 us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAuthorized / us-gaap_PlanNameAxis = osbc_EquityIncentivePlan2014Member |  |
Number of shares issuable | 210,500 us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrant / us-gaap_PlanNameAxis = osbc_EquityIncentivePlan2014Member |  |
Stock options |  |  |
Equity Compensation Plans |  |  |
Granted (in shares) | 0 us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodGross / us-gaap_AwardTypeAxis = osbc_EmployeeAndNonemployeeStockOptionsMember | 0 us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodGross / us-gaap_AwardTypeAxis = osbc_EmployeeAndNonemployeeStockOptionsMember | 0 us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodGross / us-gaap_AwardTypeAxis = osbc_EmployeeAndNonemployeeStockOptionsMember
Term of stock options granted | 10 years |  |
Exercised (in shares) | 0 us-gaap_StockIssuedDuringPeriodSharesStockOptionsExercised / us-gaap_AwardTypeAxis = osbc_EmployeeAndNonemployeeStockOptionsMember | 0 us-gaap_StockIssuedDuringPeriodSharesStockOptionsExercised / us-gaap_AwardTypeAxis = osbc_EmployeeAndNonemployeeStockOptionsMember |
Total unrecognized compensation cost | 0 us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedStockOptions / us-gaap_AwardTypeAxis = osbc_EmployeeAndNonemployeeStockOptionsMember |  |
Shares |  |  |
Beginning outstanding (in shares) | 325,500 us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber / us-gaap_AwardTypeAxis = osbc_EmployeeAndNonemployeeStockOptionsMember |  |
Expired (in shares) | (89,500)us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExpirationsInPeriod / us-gaap_AwardTypeAxis = osbc_EmployeeAndNonemployeeStockOptionsMember |  |
Ending outstanding (in shares) | 229,000 us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber / us-gaap_AwardTypeAxis = osbc_EmployeeAndNonemployeeStockOptionsMember | 325,500 us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber / us-gaap_AwardTypeAxis = osbc_EmployeeAndNonemployeeStockOptionsMember |
Exercisable at end of period (in shares) | 229,000 us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisableNumber / us-gaap_AwardTypeAxis = osbc_EmployeeAndNonemployeeStockOptionsMember |  |
Weighted Average Exercise Price |  |  |
Beginning outstanding (in dollars per share) | $ 29.56 us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePrice / us-gaap_AwardTypeAxis = osbc_EmployeeAndNonemployeeStockOptionsMember |  |
Expired (in dollars per share) | $ 32.59 us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsExpirationsInPeriodWeightedAverageExercisePrice / us-gaap_AwardTypeAxis = osbc_EmployeeAndNonemployeeStockOptionsMember |  |
Ending outstanding (in dollars per share) | $ 28.28 us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePrice / us-gaap_AwardTypeAxis = osbc_EmployeeAndNonemployeeStockOptionsMember | $ 29.56 us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePrice / us-gaap_AwardTypeAxis = osbc_EmployeeAndNonemployeeStockOptionsMember |
Exercisable at end of period (in dollars per share) | $ 28.28 us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisableWeightedAverageExercisePrice / us-gaap_AwardTypeAxis = osbc_EmployeeAndNonemployeeStockOptionsMember |  |
Weighted Average Remaining Contractual Term (years) |  |  |
Ending outstanding (in years) | 2 years 2 months 12 days |  |
Exercisable at end of period | 2 years 2 months 12 days |  |
Restricted stock and restricted stock units |  |  |
Equity Compensation Plans |  |  |
Vesting period | 3 years |  |
Nonvested shares of restricted shares rights |  |  |
Nonvested at the beginning of the period (in shares) | 185,500 us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber / us-gaap_AwardTypeAxis = osbc_RestrictedStockAndRestrictedStockUnitsMember |  |
Granted (in shares) | 184,500 us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod / us-gaap_AwardTypeAxis = osbc_RestrictedStockAndRestrictedStockUnitsMember | 155,500 us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod / us-gaap_AwardTypeAxis = osbc_RestrictedStockAndRestrictedStockUnitsMember |
Vested (in shares) | (25,000)us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriod / us-gaap_AwardTypeAxis = osbc_RestrictedStockAndRestrictedStockUnitsMember |  |
Forfeited (in shares) | (20,000)us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeitedInPeriod / us-gaap_AwardTypeAxis = osbc_RestrictedStockAndRestrictedStockUnitsMember |  |
Nonvested at the end of the period (in shares) | 325,000 us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber / us-gaap_AwardTypeAxis = osbc_RestrictedStockAndRestrictedStockUnitsMember | 185,500 us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber / us-gaap_AwardTypeAxis = osbc_RestrictedStockAndRestrictedStockUnitsMember |
Weighted Average Grant Date Fair Value |  |  |
Nonvested at the beginning of the period (in dollars per share) | $ 2.95 us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue / us-gaap_AwardTypeAxis = osbc_RestrictedStockAndRestrictedStockUnitsMember |  |
Granted (in dollars per share) | $ 4.82 us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue / us-gaap_AwardTypeAxis = osbc_RestrictedStockAndRestrictedStockUnitsMember |  |
Vested (in dollars per share) | $ 2.06 us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriodWeightedAverageGrantDateFairValue / us-gaap_AwardTypeAxis = osbc_RestrictedStockAndRestrictedStockUnitsMember |  |
Forfeited (in dollars per share) | $ 1.74 us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeituresWeightedAverageGrantDateFairValue / us-gaap_AwardTypeAxis = osbc_RestrictedStockAndRestrictedStockUnitsMember |  |
Nonvested at the end of the period (in dollars per share) | $ 4.15 us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue / us-gaap_AwardTypeAxis = osbc_RestrictedStockAndRestrictedStockUnitsMember | $ 2.95 us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue / us-gaap_AwardTypeAxis = osbc_RestrictedStockAndRestrictedStockUnitsMember |
Total unrecognized compensation cost of restricted awards | $ 885,000 us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedShareBasedAwardsOtherThanOptions / us-gaap_AwardTypeAxis = osbc_RestrictedStockAndRestrictedStockUnitsMember |  |
Expected weighted-average period for recognition of unrecognized compensation | 2 years 2 months 27 days |  |

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- Definition Represents the expense recognized during the period arising from equity-based compensation arrangements (for example, shares of stock, unit, stock options or other equity instruments) with employees, directors and certain consultants qualifying for treatment as employees. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 1 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5047-113901 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SAB TOPIC 14.F) -URI http://asc.fasb.org/extlink&oid=27013229&loc=d3e301413-122809 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (h)(1)(i) -URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901 Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Staff Accounting Bulletin (SAB) -Number Topic 14 -Section F + Details
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- Definition Weighted average fair value as of the grant date of equity-based award plans other than stock (unit) option plans that were not exercised or put into effect as a result of the occurrence of a terminating event. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (c)(2)(iii)(3) -URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901 + Details
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- Definition The number of grants made during the period on other than stock (or unit) option plans (for example, phantom stock or unit plan, stock or unit appreciation rights plan, performance target plan). + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (c)(2)(iii)(1) -URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901 + Details
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- Definition The weighted average fair value at grant date for nonvested equity-based awards issued during the period on other than stock (or unit) option plans (for example, phantom stock or unit plan, stock or unit appreciation rights plan, performance target plan). + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (c)(2)(iii)(1) -URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901 + Details
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- Definition The number of non-vested equity-based payment instruments, excluding stock (or unit) options, that validly exist and are outstanding as of the balance sheet date. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (c)(2)(i)-(ii) -URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901 + Details
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- Definition The weighted average fair value of nonvested awards on equity-based plans excluding option plans (for example, phantom stock or unit plan, stock or unit appreciation rights plan, revenue or profit achievement stock award plan) for which the employer is contingently obligated to issue equity instruments or transfer assets to an employee who has not yet satisfied service or performance criteria necessary to gain title to proceeds from the sale of the award or underlying shares or units. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (c)(2)(i)-(ii) -URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901 + Details
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- Definition The number of equity-based payment instruments, excluding stock (or unit) options, that vested during the reporting period. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (c)(2)(iii)(2) -URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901 + Details
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- Definition The weighted average fair value as of grant date pertaining to an equity-based award plan other than a stock (or unit) option plan for which the grantee gained the right during the reporting period, by satisfying service and performance requirements, to receive or retain shares or units, other instruments, or cash in accordance with the terms of the arrangement. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (c)(2)(iii)(2) -URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901 + Details
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- Definition The maximum number of shares (or other type of equity) originally approved (usually by shareholders and board of directors), net of any subsequent amendments and adjustments, for awards under the equity-based compensation plan. As stock or unit options and equity instruments other than options are awarded to participants, the shares or units remain authorized and become reserved for issuance under outstanding awards (not necessarily vested). + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (a)(3) -URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901 + Details
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- Definition The difference between the maximum number of shares (or other type of equity) authorized for issuance under the plan (including the effects of amendments and adjustments), and the sum of: 1) the number of shares (or other type of equity) already issued upon exercise of options or other equity-based awards under the plan; and 2) shares (or other type of equity) reserved for issuance on granting of outstanding awards, net of cancellations and forfeitures, if applicable. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901 + Details
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- Definition The number of shares into which fully or partially vested stock options outstanding as of the balance sheet date can be currently converted under the option plan. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (c)(1)(iii) -URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901 + Details
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- Definition Number of options or other stock instruments for which the right to exercise has lapsed under the terms of the plan agreements. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (c)(1)(iv)(4) -URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901 + Details
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- Definition The number of shares under options that were cancelled during the reporting period as a result of occurrence of a terminating event specified in contractual agreements pertaining to the stock option plan. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (c)(1)(iv)(3) -URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901 + Details
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- Definition Gross number of share options (or share units) granted during the period. + References No definition available. + Details
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- Definition Number of options outstanding, including both vested and non-vested options. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (c)(1)(i)-(ii) -URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901 + Details
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- Definition Weighted average price at which grantees can acquire the shares reserved for issuance under the stock option plan. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (c)(1)(i) -URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901 + Details
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- Definition Weighted average remaining contractual term for option awards outstanding, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (e)(1) -URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901 + Details
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- Definition Weighted average price at which grantees could have acquired the underlying shares with respect to stock options of the plan that expired. + References No definition available. + Details
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