XML 87 R68.htm IDEA: XBRL DOCUMENT
v3.25.0.1

Loans and Allowance for Credit Losses on Loans - Credit Quality (Details) - USD ($) | 12 Months Ended |
--- | --- | ---
Dec. 31, 2024 | Dec. 31, 2023
The gross charge-offs activity by loan type and year of origination |  |
2024 / 2023 | $ 988,880,000 | $ 965,644,000
2023 / 2022 | 740,096,000 | 997,009,000
2022/ 2021 | 808,157,000 | 737,065,000
2021 / 2020 | 537,229,000 | 367,981,000
2020/ 2019 | 251,786,000 | 192,786,000
Prior | 311,052,000 | 306,846,000
Revolving Loans | 342,857,000 | 474,214,000
Revolving Loans Converted To Term Loans | 1,279,000 | 1,408,000
Total Loans | 3,981,336,000 | 4,042,953,000
Minimum |  |
The gross charge-offs activity by loan type and year of origination |  |
Loan commitment for inclusion in credit quality analysis | 50,000 |
Pass |  |
The gross charge-offs activity by loan type and year of origination |  |
2024 / 2023 | 984,681,000 | 963,994,000
2023 / 2022 | 735,516,000 | 958,129,000
2022/ 2021 | 765,954,000 | 682,010,000
2021 / 2020 | 516,166,000 | 344,237,000
2020/ 2019 | 238,614,000 | 158,932,000
Prior | 289,683,000 | 280,746,000
Revolving Loans | 319,558,000 | 450,136,000
Revolving Loans Converted To Term Loans | 1,279,000 | 1,408,000
Total Loans | 3,851,451,000 | 3,839,592,000
Special Mention |  |
The gross charge-offs activity by loan type and year of origination |  |
2024 / 2023 | 3,864,000 | 1,650,000
2023 / 2022 | 2,791,000 | 20,320,000
2022/ 2021 | 15,650,000 | 35,050,000
2021 / 2020 | 7,676,000 | 3,621,000
2020/ 2019 | 3,033,000 | 1,863,000
Prior | 975,000 | 3,681,000
Revolving Loans | 3,903,000 | 4,392,000
Total Loans | 37,892,000 | 70,577,000
Substandard |  |
The gross charge-offs activity by loan type and year of origination |  |
2024 / 2023 | 335,000 |
2023 / 2022 | 1,789,000 | 18,560,000
2022/ 2021 | 26,553,000 | 20,005,000
2021 / 2020 | 12,001,000 | 20,123,000
2020/ 2019 | 10,139,000 | 31,991,000
Prior | 20,394,000 | 22,419,000
Revolving Loans | 19,396,000 | 19,686,000
Total Loans | 90,607,000 | 132,784,000
Doubtful [Member] |  |
The gross charge-offs activity by loan type and year of origination |  |
2021 / 2020 | 1,386,000 |
Total Loans | 1,386,000 |
Commercial |  |
The gross charge-offs activity by loan type and year of origination |  |
2024 / 2023 | 303,727,000 | 318,569,000
2023 / 2022 | 178,192,000 | 141,504,000
2022/ 2021 | 60,915,000 | 36,754,000
2021 / 2020 | 20,318,000 | 12,154,000
2020/ 2019 | 4,999,000 | 18,589,000
Prior | 6,527,000 | 3,426,000
Revolving Loans | 224,519,000 | 309,293,000
Revolving Loans Converted To Term Loans | 1,279,000 | 1,408,000
Total Loans | 800,476,000 | 841,697,000
Commercial | Pass |  |
The gross charge-offs activity by loan type and year of origination |  |
2024 / 2023 | 299,863,000 | 318,569,000
2023 / 2022 | 176,549,000 | 136,668,000
2022/ 2021 | 56,619,000 | 35,901,000
2021 / 2020 | 18,679,000 | 11,983,000
2020/ 2019 | 4,999,000 | 18,390,000
Prior | 6,527,000 | 3,426,000
Revolving Loans | 201,514,000 | 298,931,000
Revolving Loans Converted To Term Loans | 1,279,000 | 1,408,000
Total Loans | 766,029,000 | 825,276,000
Commercial | Special Mention |  |
The gross charge-offs activity by loan type and year of origination |  |
2024 / 2023 | 3,864,000 |
2023 / 2022 | 1,629,000 | 2,737,000
2022/ 2021 | 127,000 | 707,000
2021 / 2020 | 176,000 | 171,000
Revolving Loans | 3,903,000 | 4,392,000
Total Loans | 9,699,000 | 8,007,000
Commercial | Substandard |  |
The gross charge-offs activity by loan type and year of origination |  |
2023 / 2022 | 14,000 | 2,099,000
2022/ 2021 | 4,169,000 | 146,000
2021 / 2020 | 77,000 |
2020/ 2019 |  | 199,000
Revolving Loans | 19,102,000 | 5,970,000
Total Loans | 23,362,000 | 8,414,000
Commercial | Doubtful [Member] |  |
The gross charge-offs activity by loan type and year of origination |  |
2021 / 2020 | 1,386,000 |
Total Loans | 1,386,000 |
Real estate - residential loans |  |
The gross charge-offs activity by loan type and year of origination |  |
Mortgage loans in process of foreclosure | 469,000 | 170,000
Leases |  |
The gross charge-offs activity by loan type and year of origination |  |
2024 / 2023 | 239,664,000 | 219,163,000
2023 / 2022 | 151,372,000 | 113,481,000
2022/ 2021 | 67,723,000 | 42,478,000
2021 / 2020 | 24,546,000 | 14,663,000
2020/ 2019 | 6,145,000 | 7,183,000
Prior | 2,298,000 | 1,255,000
Total Loans | 491,748,000 | 398,223,000
Leases | Pass |  |
The gross charge-offs activity by loan type and year of origination |  |
2024 / 2023 | 239,664,000 | 219,163,000
2023 / 2022 | 151,372,000 | 113,074,000
2022/ 2021 | 66,379,000 | 42,275,000
2021 / 2020 | 24,546,000 | 14,663,000
2020/ 2019 | 6,145,000 | 6,975,000
Prior | 2,298,000 | 1,255,000
Total Loans | 490,404,000 | 397,405,000
Leases | Special Mention |  |
The gross charge-offs activity by loan type and year of origination |  |
2022/ 2021 | 821,000 |
Total Loans | 821,000 |
Leases | Substandard |  |
The gross charge-offs activity by loan type and year of origination |  |
2023 / 2022 |  | 407,000
2022/ 2021 | 523,000 | 203,000
2020/ 2019 |  | 208,000
Total Loans | 523,000 | 818,000
Commercial real estate - Investor |  |
The gross charge-offs activity by loan type and year of origination |  |
2024 / 2023 | 244,318,000 | 159,654,000
2023 / 2022 | 160,653,000 | 367,512,000
2022/ 2021 | 305,506,000 | 230,189,000
2021 / 2020 | 191,651,000 | 113,711,000
2020/ 2019 | 90,245,000 | 69,980,000
Prior | 79,652,000 | 72,929,000
Revolving Loans | 6,804,000 | 20,449,000
Total Loans | 1,078,829,000 | 1,034,424,000
Commercial real estate - Investor | Pass |  |
The gross charge-offs activity by loan type and year of origination |  |
2024 / 2023 | 243,983,000 | 159,654,000
2023 / 2022 | 159,008,000 | 367,512,000
2022/ 2021 | 305,506,000 | 218,084,000
2021 / 2020 | 191,651,000 | 108,384,000
2020/ 2019 | 90,245,000 | 54,322,000
Prior | 67,143,000 | 63,281,000
Revolving Loans | 6,804,000 | 8,122,000
Total Loans | 1,064,340,000 | 979,359,000
Commercial real estate - Investor | Special Mention |  |
The gross charge-offs activity by loan type and year of origination |  |
2022/ 2021 |  | 11,267,000
Total Loans |  | 11,267,000
Commercial real estate - Investor | Substandard |  |
The gross charge-offs activity by loan type and year of origination |  |
2024 / 2023 | 335,000 |
2023 / 2022 | 1,645,000 |
2022/ 2021 |  | 838,000
2021 / 2020 |  | 5,327,000
2020/ 2019 |  | 15,658,000
Prior | 12,509,000 | 9,648,000
Revolving Loans |  | 12,327,000
Total Loans | 14,489,000 | 43,798,000
Commercial real estate - Owner occupied |  |
The gross charge-offs activity by loan type and year of origination |  |
2024 / 2023 | 91,012,000 | 125,709,000
2023 / 2022 | 115,542,000 | 166,428,000
2022/ 2021 | 142,564,000 | 205,955,000
2021 / 2020 | 140,393,000 | 110,808,000
2020/ 2019 | 90,849,000 | 57,866,000
Prior | 88,639,000 | 96,529,000
Revolving Loans | 14,284,000 | 33,243,000
Total Loans | 683,283,000 | 796,538,000
Commercial real estate - Owner occupied | Pass |  |
The gross charge-offs activity by loan type and year of origination |  |
2024 / 2023 | 91,012,000 | 124,059,000
2023 / 2022 | 114,255,000 | 134,383,000
2022/ 2021 | 133,488,000 | 177,553,000
2021 / 2020 | 121,652,000 | 103,109,000
2020/ 2019 | 77,919,000 | 42,839,000
Prior | 82,820,000 | 91,062,000
Revolving Loans | 14,284,000 | 33,243,000
Total Loans | 635,430,000 | 706,248,000
Commercial real estate - Owner occupied | Special Mention |  |
The gross charge-offs activity by loan type and year of origination |  |
2024 / 2023 |  | 1,650,000
2023 / 2022 | 1,162,000 | 17,415,000
2022/ 2021 | 7,908,000 | 9,585,000
2021 / 2020 | 7,500,000 | 3,128,000
2020/ 2019 | 3,033,000 | 218,000
Prior | 631,000 | 3,681,000
Total Loans | 20,234,000 | 35,677,000
Commercial real estate - Owner occupied | Substandard |  |
The gross charge-offs activity by loan type and year of origination |  |
2023 / 2022 | 125,000 | 14,630,000
2022/ 2021 | 1,168,000 | 18,817,000
2021 / 2020 | 11,241,000 | 4,571,000
2020/ 2019 | 9,897,000 | 14,809,000
Prior | 5,188,000 | 1,786,000
Total Loans | 27,619,000 | 54,613,000
Construction |  |
The gross charge-offs activity by loan type and year of origination |  |
2024 / 2023 | 44,699,000 | 42,808,000
2023 / 2022 | 27,928,000 | 66,513,000
2022/ 2021 | 109,367,000 | 32,942,000
2021 / 2020 | 17,747,000 | 10,093,000
2020/ 2019 | 82,000 | 1,593,000
Prior | 1,425,000 | 8,245,000
Revolving Loans | 468,000 | 3,186,000
Total Loans | 201,716,000 | 165,380,000
Construction | Pass |  |
The gross charge-offs activity by loan type and year of origination |  |
2024 / 2023 | 44,699,000 | 42,808,000
2023 / 2022 | 27,928,000 | 66,513,000
2022/ 2021 | 83,222,000 | 32,942,000
2021 / 2020 | 17,747,000 | 100,000
2020/ 2019 | 82,000 | 1,593,000
Prior | 1,081,000 | 1,083,000
Revolving Loans | 468,000 | 3,186,000
Total Loans | 175,227,000 | 148,225,000
Construction | Special Mention |  |
The gross charge-offs activity by loan type and year of origination |  |
2022/ 2021 | 6,794,000 |
Prior | 344,000 |
Total Loans | 7,138,000 |
Construction | Substandard |  |
The gross charge-offs activity by loan type and year of origination |  |
2022/ 2021 | 19,351,000 |
2021 / 2020 |  | 9,993,000
Prior |  | 7,162,000
Total Loans | 19,351,000 | 17,155,000
Residential real estate - Investor |  |
The gross charge-offs activity by loan type and year of origination |  |
2024 / 2023 | 5,595,000 | 5,062,000
2023 / 2022 | 3,833,000 | 14,824,000
2022/ 2021 | 13,741,000 | 9,093,000
2021 / 2020 | 8,592,000 | 6,227,000
2020/ 2019 | 5,693,000 | 6,916,000
Prior | 10,596,000 | 9,002,000
Revolving Loans | 1,548,000 | 1,471,000
Total Loans | 49,598,000 | 52,595,000
Residential real estate - Investor | Pass |  |
The gross charge-offs activity by loan type and year of origination |  |
2024 / 2023 | 5,595,000 | 5,062,000
2023 / 2022 | 3,833,000 | 14,434,000
2022/ 2021 | 13,366,000 | 9,027,000
2021 / 2020 | 8,060,000 | 6,227,000
2020/ 2019 | 5,693,000 | 6,508,000
Prior | 9,813,000 | 8,469,000
Revolving Loans | 1,548,000 | 1,471,000
Total Loans | 47,908,000 | 51,198,000
Residential real estate - Investor | Special Mention |  |
The gross charge-offs activity by loan type and year of origination |  |
2022/ 2021 |  | 66,000
Total Loans |  | 66,000
Residential real estate - Investor | Substandard |  |
The gross charge-offs activity by loan type and year of origination |  |
2023 / 2022 |  | 390,000
2022/ 2021 | 375,000 |
2021 / 2020 | 532,000 |
2020/ 2019 |  | 408,000
Prior | 783,000 | 533,000
Total Loans | 1,690,000 | 1,331,000
Residential real estate - Owner occupied |  |
The gross charge-offs activity by loan type and year of origination |  |
2024 / 2023 | 11,609,000 | 32,574,000
2023 / 2022 | 29,670,000 | 41,528,000
2022/ 2021 | 35,786,000 | 40,335,000
2021 / 2020 | 32,911,000 | 25,513,000
2020/ 2019 | 22,996,000 | 14,918,000
Prior | 73,207,000 | 70,617,000
Revolving Loans | 770,000 | 763,000
Total Loans | 206,949,000 | 226,248,000
Residential real estate - Owner occupied | Pass |  |
The gross charge-offs activity by loan type and year of origination |  |
2024 / 2023 | 11,609,000 | 32,574,000
2023 / 2022 | 29,670,000 | 41,528,000
2022/ 2021 | 35,786,000 | 40,335,000
2021 / 2020 | 32,760,000 | 25,322,000
2020/ 2019 | 22,996,000 | 14,233,000
Prior | 71,507,000 | 68,277,000
Revolving Loans | 770,000 | 763,000
Total Loans | 205,098,000 | 223,032,000
Residential real estate - Owner occupied | Substandard |  |
The gross charge-offs activity by loan type and year of origination |  |
2021 / 2020 | 151,000 | 191,000
2020/ 2019 |  | 685,000
Prior | 1,700,000 | 2,340,000
Total Loans | 1,851,000 | 3,216,000
Multifamily |  |
The gross charge-offs activity by loan type and year of origination |  |
2024 / 2023 | 39,133,000 | 55,310,000
2023 / 2022 | 68,781,000 | 80,237,000
2022/ 2021 | 68,994,000 | 137,259,000
2021 / 2020 | 100,049,000 | 72,861,000
2020/ 2019 | 29,263,000 | 13,876,000
Prior | 44,735,000 | 41,591,000
Revolving Loans | 370,000 | 562,000
Total Loans | 351,325,000 | 401,696,000
Multifamily | Pass |  |
The gross charge-offs activity by loan type and year of origination |  |
2024 / 2023 | 39,133,000 | 55,310,000
2023 / 2022 | 68,781,000 | 79,060,000
2022/ 2021 | 68,032,000 | 123,834,000
2021 / 2020 | 100,049,000 | 72,539,000
2020/ 2019 | 29,060,000 | 12,231,000
Prior | 44,735,000 | 40,825,000
Revolving Loans | 370,000 | 562,000
Total Loans | 350,160,000 | 384,361,000
Multifamily | Special Mention |  |
The gross charge-offs activity by loan type and year of origination |  |
2023 / 2022 |  | 168,000
2022/ 2021 |  | 13,425,000
2021 / 2020 |  | 322,000
2020/ 2019 |  | 1,645,000
Total Loans |  | 15,560,000
Multifamily | Substandard |  |
The gross charge-offs activity by loan type and year of origination |  |
2023 / 2022 |  | 1,009,000
2022/ 2021 | 962,000 |
2020/ 2019 | 203,000 |
Prior |  | 766,000
Total Loans | 1,165,000 | 1,775,000
HELOC |  |
The gross charge-offs activity by loan type and year of origination |  |
2024 / 2023 | 2,602,000 | 2,735,000
2023 / 2022 | 2,561,000 | 2,704,000
2022/ 2021 | 2,118,000 | 491,000
2021 / 2020 | 383,000 | 1,798,000
2020/ 2019 | 1,422,000 | 1,780,000
Prior | 3,966,000 | 3,179,000
Revolving Loans | 90,336,000 | 90,550,000
Total Loans | 103,388,000 | 103,237,000
HELOC | Pass |  |
The gross charge-offs activity by loan type and year of origination |  |
2024 / 2023 | 2,602,000 | 2,735,000
2023 / 2022 | 2,561,000 | 2,679,000
2022/ 2021 | 2,118,000 | 490,000
2021 / 2020 | 383,000 | 1,757,000
2020/ 2019 | 1,383,000 | 1,756,000
Prior | 3,752,000 | 2,995,000
Revolving Loans | 90,042,000 | 89,161,000
Total Loans | 102,841,000 | 101,573,000
HELOC | Substandard |  |
The gross charge-offs activity by loan type and year of origination |  |
2023 / 2022 |  | 25,000
2022/ 2021 |  | 1,000
2021 / 2020 |  | 41,000
2020/ 2019 | 39,000 | 24,000
Prior | 214,000 | 184,000
Revolving Loans | 294,000 | 1,389,000
Total Loans | 547,000 | 1,664,000
Other |  |
The gross charge-offs activity by loan type and year of origination |  |
2024 / 2023 | 6,521,000 | 4,060,000
2023 / 2022 | 1,564,000 | 2,278,000
2022/ 2021 | 1,443,000 | 1,569,000
2021 / 2020 | 639,000 | 153,000
2020/ 2019 | 92,000 | 85,000
Prior | 7,000 | 73,000
Revolving Loans | 3,758,000 | 14,697,000
Total Loans | 14,024,000 | 22,915,000
Other | Pass |  |
The gross charge-offs activity by loan type and year of origination |  |
2024 / 2023 | 6,521,000 | 4,060,000
2023 / 2022 | 1,559,000 | 2,278,000
2022/ 2021 | 1,438,000 | 1,569,000
2021 / 2020 | 639,000 | 153,000
2020/ 2019 | 92,000 | 85,000
Prior | 7,000 | 73,000
Revolving Loans | 3,758,000 | 14,697,000
Total Loans | 14,014,000 | $ 22,915,000
Other | Substandard |  |
The gross charge-offs activity by loan type and year of origination |  |
2023 / 2022 | 5,000 |
2022/ 2021 | 5,000 |
Total Loans | $ 10,000 |

X
- Definition Amortized cost excluding accrued interest, before allowance for credit loss, of financing receivable and net investment in lease. + References No definition available. + Details
Name: | osbc_FinancingReceivableAndNetInvestmentInLeaseExcludingAccruedInterestBeforeAllowanceForCreditLoss
Namespace Prefix: | osbc_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Amortized cost excluding accrued interest, of financing receivable and net investment in lease originated more than five years prior to current fiscal year. + References No definition available. + Details
Name: | osbc_FinancingReceivableAndNetInvestmentInLeaseExcludingAccruedInterestOriginatedMoreThanFiveYearsBeforeCurrentFiscalYear
Namespace Prefix: | osbc_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Amortized cost excluding accrued interest, of financing receivable and net investment in lease originated four years prior to current fiscal year. + References No definition available. + Details
Name: | osbc_FinancingReceivableAndNetInvestmentInLeaseExcludingAccruedInterestYearFiveOriginatedFourYearsBeforeFiscalYear
Namespace Prefix: | osbc_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Amortized cost excluding accrued interest, of financing receivable and net investment in lease originated three years prior to current fiscal year. + References No definition available. + Details
Name: | osbc_FinancingReceivableAndNetInvestmentInLeaseExcludingAccruedInterestYearFourOriginatedThreeYearsBeforeFiscalYear
Namespace Prefix: | osbc_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Amortized cost excluding accrued interest, of financing receivable and net investment in lease originated in current fiscal year. + References No definition available. + Details
Name: | osbc_FinancingReceivableAndNetInvestmentInLeaseExcludingAccruedInterestYearOneOriginatedCurrentFiscalYear
Namespace Prefix: | osbc_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Amortized cost excluding accrued interest, of financing receivable and net investment in lease originated two years prior to current fiscal year. + References No definition available. + Details
Name: | osbc_FinancingReceivableAndNetInvestmentInLeaseExcludingAccruedInterestYearThreeOriginatedTwoYearsBeforeFiscalYear
Namespace Prefix: | osbc_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Amortized cost excluding accrued interest, of financing receivable and net investment in lease originated in fiscal year prior to current fiscal year. + References No definition available. + Details
Name: | osbc_FinancingReceivableAndNetInvestmentInLeaseExcludingAccruedInterestYearTwoOriginatedFiscalYearBeforeFiscalYear
Namespace Prefix: | osbc_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition The outstanding loan commitment to be included in credit quality indicator analysis. + References No definition available. + Details
Name: | osbc_OutstandingLoanCommitmentsThresholdForCreditQualityCategorizing
Namespace Prefix: | osbc_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

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

X
- Definition Amortized cost excluding accrued interest, of financing receivable that can be withdrawn, repaid, and redrawn. + References Reference 1: http://www.xbrl.org/2003/role/exampleRef -Topic 326 -SubTopic 20 -Name Accounting Standards Codification -Section 55 -Paragraph 79 -Publisher FASB -URI https://asc.fasb.org//1943274/2147479294/326-20-55-79 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Topic 326 -SubTopic 20 -Name Accounting Standards Codification -Section 50 -Paragraph 6 -Publisher FASB -URI https://asc.fasb.org//1943274/2147479319/326-20-50-6 Reference 3: http://www.xbrl.org/2003/role/disclosureRef -Topic 326 -SubTopic 20 -Name Accounting Standards Codification -Section 50 -Paragraph 3B -Publisher FASB -URI https://asc.fasb.org//1943274/2147479319/326-20-50-3B + Details
Name: | us-gaap_FinancingReceivableExcludingAccruedInterestRevolving
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Amortized cost excluding accrued interest, of revolving financing receivable converted to term loan. + References Reference 1: http://www.xbrl.org/2003/role/exampleRef -Topic 326 -SubTopic 20 -Name Accounting Standards Codification -Section 55 -Paragraph 79 -Publisher FASB -URI https://asc.fasb.org//1943274/2147479294/326-20-55-79 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Topic 326 -SubTopic 20 -Name Accounting Standards Codification -Section 50 -Paragraph 6A -Publisher FASB -URI https://asc.fasb.org//1943274/2147479319/326-20-50-6A Reference 3: http://www.xbrl.org/2003/role/disclosureRef -Topic 326 -SubTopic 20 -Name Accounting Standards Codification -Section 50 -Paragraph 3B -Publisher FASB -URI https://asc.fasb.org//1943274/2147479319/326-20-50-3B + Details
Name: | us-gaap_FinancingReceivableExcludingAccruedInterestRevolvingConvertedToTermLoan
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Recorded investment of consumer mortgage loan receivables secured by residential real estate properties for which formal foreclosure proceedings are in process. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Name Accounting Standards Codification -Section 50 -Paragraph 35 -SubTopic 10 -Topic 310 -Publisher FASB -URI https://asc.fasb.org//1943274/2147481962/310-10-50-35 + Details
Name: | us-gaap_MortgageLoansInProcessOfForeclosureAmount
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Details
Name: | srt_RangeAxis=srt_MinimumMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_InternalCreditAssessmentAxis=us-gaap_PassMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_InternalCreditAssessmentAxis=us-gaap_SpecialMentionMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_InternalCreditAssessmentAxis=us-gaap_SubstandardMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_InternalCreditAssessmentAxis=us-gaap_DoubtfulMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_FinancingReceivablePortfolioSegmentAxis=us-gaap_CommercialPortfolioSegmentMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_FinancingReceivablePortfolioSegmentAxis=us-gaap_ResidentialPortfolioSegmentMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_FinancingReceivablePortfolioSegmentAxis=us-gaap_FinanceLeasesPortfolioSegmentMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_FinancingReceivablePortfolioSegmentAxis=osbc_CommercialRealEstateInvestorMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_FinancingReceivablePortfolioSegmentAxis=osbc_CommercialRealEstateOwnerOccupiedMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_FinancingReceivablePortfolioSegmentAxis=us-gaap_ConstructionMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_FinancingReceivablePortfolioSegmentAxis=osbc_RealEstateInvestorMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_FinancingReceivablePortfolioSegmentAxis=osbc_RealEstateOwnerOccupiedMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_FinancingReceivablePortfolioSegmentAxis=osbc_MultiFamilyLoanMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_FinancingReceivablePortfolioSegmentAxis=us-gaap_HomeEquityMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_FinancingReceivablePortfolioSegmentAxis=us-gaap_UnallocatedFinancingReceivablesMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |