XML 71 R55.htm IDEA: XBRL DOCUMENT
v3.8.0.1

Securities - Amortized Cost and Fair Value (Details) - USD ($) | 12 Months Ended
--- | ---
Dec. 31, 2017 | Dec. 31, 2016 | Dec. 31, 2015
Securities Available-for-Sale |  |  |
Amortized Cost | $ 537,645,000 | $ 545,433,000 |
Gross Unrealized Gains | 8,467,000 | 1,011,000 |
Gross Unrealized Losses | (4,673,000) | (14,606,000) |
Fair Value | 541,439,000 | 531,838,000 |
Other disclosures |  |  |
Purchases | 343,470,000 | 210,681,000 | $ 196,082,000
Sales | 232,462,000.000 | 306,400,000.000 | $ 70,176,000.000
Securities pledged to secure deposits and for other purposes | 301,000,000 | 262,600,000 |
U.S. Treasury |  |  |
Securities Available-for-Sale |  |  |
Amortized Cost | 4,002,000 |  |
Gross Unrealized Losses | (55,000) |  |
Fair Value | 3,947,000 |  |
US Treasury and Government |  |  |
Securities Available-for-Sale |  |  |
Amortized Cost | 13,062,000 |  |
Gross Unrealized Gains | 8,000 |  |
Gross Unrealized Losses | (9,000) |  |
Fair Value | 13,061,000 |  |
U.S. government agencies |  |  |
Securities Available-for-Sale |  |  |
Fair Value | 13,061,000 |  |
U.S. government agencies mortgage-backed |  |  |
Securities Available-for-Sale |  |  |
Amortized Cost | 12,372,000 | 42,511,000 |
Gross Unrealized Gains | 7,000 |  |
Gross Unrealized Losses | (165,000) | (977,000) |
Fair Value | 12,214,000 | 41,534,000 |
States and political subdivisions |  |  |
Securities Available-for-Sale |  |  |
Amortized Cost | 272,240,000 | 68,718,000 |
Gross Unrealized Gains | 7,116,000 | 258,000 |
Gross Unrealized Losses | (1,264,000) | (273,000) |
Fair Value | 278,092,000 | 68,703,000 |
Corporate bonds |  |  |
Securities Available-for-Sale |  |  |
Amortized Cost | 823,000 | 10,957,000 |
Gross Unrealized Gains | 21,000 | 9,000 |
Gross Unrealized Losses | (11,000) | (336,000) |
Fair Value | 833,000 | 10,630,000 |
Collateralized mortgage obligations |  |  |
Securities Available-for-Sale |  |  |
Amortized Cost | 66,892,000 | 174,352,000 |
Gross Unrealized Gains | 202,000 | 374,000 |
Gross Unrealized Losses | (1,155,000) | (3,799,000) |
Fair Value | 65,939,000 | 170,927,000 |
Asset-backed securities |  |  |
Securities Available-for-Sale |  |  |
Amortized Cost | 113,983,000 | 146,391,000 |
Gross Unrealized Gains | 862,000 | 341,000 |
Gross Unrealized Losses | (1,913,000) | (8,325,000) |
Fair Value | 112,932,000 | 138,407,000 |
Collateralized loan obligations |  |  |
Securities Available-for-Sale |  |  |
Amortized Cost | 54,271,000 | 102,504,000 |
Gross Unrealized Gains | 251,000 | 29,000 |
Gross Unrealized Losses | (101,000) | (896,000) |
Fair Value | 54,421,000 | $ 101,637,000 |
U.S. government agency mortgage-backed |  |  |
Securities Available-for-Sale |  |  |
Fair Value | 12,214,000 |  |
States and political subdivisions &amp; collateralized loan obligations |  |  |
Other disclosures |  |  |
Purchases | 270,200,000 |  |
Sales | 146,900,000 |  |
Paydown | 13,000,000 |  |
Talmer |  |  |
Other disclosures |  |  |
Decline in securities | 9,600,000 |  |
Stockholders' Equity | GCO Education Loan Funding Corp | Asset-backed securities | Credit Concentration Risk |  |  |
Securities Available-for-Sale |  |  |
Amortized Cost | 27,625,000 |  |
Fair Value | 26,588,000 |  |
Stockholders' Equity | Towd Point Mortgage Trust | Asset-backed securities | Credit Concentration Risk |  |  |
Securities Available-for-Sale |  |  |
Amortized Cost | 29,312,000 |  |
Fair Value | 29,210,000 |  |
Stockholders' Equity | Student Marketing Association [Member] | Asset-backed securities | Credit Concentration Risk |  |  |
Securities Available-for-Sale |  |  |
Amortized Cost | 25,696,000 |  |
Fair Value | $ 25,917,000 |  |
Minimum | Stockholders' Equity | GCO Education Loan Funding Corp | Asset-backed securities | Credit Concentration Risk |  |  |
Other disclosures |  |  |
Credit risk as a percentage of benchmark | 10.00% |  |
Minimum | Stockholders' Equity | Towd Point Mortgage Trust | Asset-backed securities | Credit Concentration Risk |  |  |
Other disclosures |  |  |
Credit risk as a percentage of benchmark | 10.00% |  |
Minimum | Stockholders' Equity | Student Marketing Association [Member] | Asset-backed securities | Credit Concentration Risk |  |  |
Other disclosures |  |  |
Credit risk as a percentage of benchmark | 10.00% |  |

X
- Definition Represents the decline in the value of overall securities for funding a business combination. + References No definition available. + Details
Name: | osbc_DeclineInSecuritiesForBusinessCombination
Namespace Prefix: | osbc_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Definition Represents the amount of paydown on securities. + References No definition available. + Details
Name: | osbc_SecuritiesPayDown
Namespace Prefix: | osbc_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition Amount of investment in debt and equity securities categorized neither as held-to-maturity nor trading. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 25 -Paragraph 1 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=75030427&loc=d3e22054-111558 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 5 -Subparagraph (aa) -URI http://asc.fasb.org/extlink&oid=82897076&loc=d3e27232-111563 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 45 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=82896770&loc=d3e26610-111562 + Details
Name: | us-gaap_AvailableForSaleSecurities
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

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

X
- Definition Amount before tax of unrealized gain in accumulated other comprehensive income (AOCI) on investments in debt and equity securities classified as available-for-sale. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=82897076&loc=d3e27161-111563 + Details
Name: | us-gaap_AvailableForSaleSecuritiesAccumulatedGrossUnrealizedGainBeforeTax
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Definition Amount before tax of unrealized loss in accumulated other comprehensive income (AOCI) on investments in debt and equity securities classified as available-for-sale. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=82897076&loc=d3e27161-111563 + Details
Name: | us-gaap_AvailableForSaleSecuritiesAccumulatedGrossUnrealizedLossBeforeTax
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition This item represents the cost of debt and equity securities, which are categorized neither as held-to-maturity nor trading, net of adjustments including accretion, amortization, collection of cash, previous other-than-temporary impairments recognized in earnings (less any cumulative-effect adjustments recognized, as defined), and fair value hedge accounting adjustments, if any. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02.2) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 + Details
Name: | us-gaap_AvailableForSaleSecuritiesAmortizedCost
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition The fair value of available-for-sale securities that serve as collateral for borrowings. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 310 -SubTopic 10 -Section 50 -Paragraph 5 -URI http://asc.fasb.org/extlink&oid=84173941&loc=d3e5086-111524 + Details
Name: | us-gaap_AvailableForSaleSecuritiesPledgedAsCollateral
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition For an entity that discloses a concentration risk in relation to quantitative amount, which serves as the "benchmark" (or denominator) in the equation, this concept represents the concentration percentage derived from the division. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 275 -SubTopic 10 -Section 50 -Paragraph 18 -URI http://asc.fasb.org/extlink&oid=84177426&loc=d3e6351-108592 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 825 -SubTopic 10 -Section 50 -Paragraph 20 -URI http://asc.fasb.org/extlink&oid=77997519&loc=d3e13531-108611 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 275 -SubTopic 10 -Section 50 -Paragraph 20 -URI http://asc.fasb.org/extlink&oid=84177426&loc=d3e6404-108592 Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 825 -SubTopic 10 -Section 50 -Paragraph 21 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=77997519&loc=d3e13537-108611 + Details
Name: | us-gaap_ConcentrationRiskPercentage1
Namespace Prefix: | us-gaap_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | duration

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

X
- Definition The cash outflow to acquire debt and equity securities not classified as either held-to-maturity securities or trading securities which would be classified as available-for-sale securities and reported at fair value, with unrealized gains and losses excluded from earnings and reported in a separate component of shareholders' equity. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 45 -Paragraph 13 -Subparagraph (a),(b) -URI http://asc.fasb.org/extlink&oid=98514028&loc=d3e3213-108585 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 45 -Paragraph 11 -URI http://asc.fasb.org/extlink&oid=82896770&loc=d3e26853-111562 + Details
Name: | us-gaap_PaymentsToAcquireAvailableForSaleSecurities
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Definition The cash inflow associated with the sale of debt and equity securities classified as available-for-sale securities. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 45 -Paragraph 11 -URI http://asc.fasb.org/extlink&oid=82896770&loc=d3e26853-111562 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 45 -Paragraph 12 -Subparagraph (a),(b) -URI http://asc.fasb.org/extlink&oid=98514028&loc=d3e3179-108585 + Details
Name: | us-gaap_ProceedsFromSaleOfAvailableForSaleSecurities
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Details
Name: | us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis=us-gaap_USTreasurySecuritiesMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis=us-gaap_USTreasuryAndGovernmentMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis=us-gaap_USGovernmentCorporationsAndAgenciesSecuritiesMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis=us-gaap_MortgageBackedSecuritiesIssuedByUSGovernmentSponsoredEnterprisesMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis=us-gaap_USStatesAndPoliticalSubdivisionsMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis=us-gaap_CorporateBondSecuritiesMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis=us-gaap_CollateralizedMortgageObligationsMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis=us-gaap_AssetBackedSecuritiesMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis=us-gaap_CollateralizedLoanObligationsMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis=osbc_MortgageBackedSecuritiesIssuedByUSGovernmentAgenciesMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis=osbc_StatesAndPoliticalSubdivisionsAndCollateralizedLoanObligationsMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_BusinessAcquisitionAxis=osbc_TalmerBancorpInc.Member
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_ConcentrationRiskByBenchmarkAxis=us-gaap_StockholdersEquityTotalMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | invest_InvestmentContractCounterpartyAxis=osbc_GCOEducationLoanFundingCorpMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_ConcentrationRiskByTypeAxis=us-gaap_CreditConcentrationRiskMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | invest_InvestmentContractCounterpartyAxis=osbc_TowdPointMortgageTrustMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | invest_InvestmentContractCounterpartyAxis=osbc_StudentMarketingAssociationMember
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: |