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Junior Subordinated Debentures - Issuance (Details) - USD ($) |  |  |  | 1 Months Ended | 3 Months Ended | 9 Months Ended |  |
--- | --- | --- | --- | --- | --- | --- | --- | ---
Sep. 30, 2020 | Mar. 02, 2020 | Feb. 24, 2020 | Apr. 30, 2007 | Sep. 30, 2019 | Sep. 30, 2020 | Sep. 30, 2019 | Dec. 31, 2019 | Dec. 31, 2016
Junior subordinated debentures |  |  |  |  |  |  |  |  |
Interest rate (as a percent) |  |  |  |  |  |  |  |  | 5.75%
Junior subordinated debentures | $ 25,773,000 |  |  |  |  | $ 25,773,000 |  | $ 57,734,000 |
Unamortized debt issuance costs |  |  |  |  |  | $ 643,000 | $ 36,000 |  |
Old Second Capital Trust II [Member] |  |  |  |  |  |  |  |  |
Junior subordinated debentures |  |  |  |  |  |  |  |  |
Proceeds from sale of cumulative trust preferred securities |  |  |  | $ 25,000,000.0 |  |  |  |  |
Maturity Period |  |  |  |  |  | 30 years |  |  |
Amortization period |  |  |  |  |  | 30 years |  |  |
Old Second Capital Trust II [Member] | Debt Instrument, Redemption, Period One [Member] |  |  |  |  |  |  |  |  |
Junior subordinated debentures |  |  |  |  |  |  |  |  |
Cash distribution rate of trust preferred securities (as a percent) | 4.40% |  |  |  | 4.40% |  |  |  |
Cash distribution fixed rate of trust preferred securities (as a percent) |  |  |  |  |  | 6.77% |  |  |
Old Second Capital Trust II [Member] | Debt Instrument, Redemption, Period Two [Member] |  |  |  |  |  |  |  |  |
Junior subordinated debentures |  |  |  |  |  |  |  |  |
Basis points added to cash distribution floating rate base (as a percent) |  |  |  |  |  | 1.50% |  |  |
Old Second Capital Trust II [Member] | Debt Instrument, Redemption, Period Two [Member] | Debt Instrument, Variable Rate Base LIBOR [Member] |  |  |  |  |  |  |  |  |
Junior subordinated debentures |  |  |  |  |  |  |  |  |
Cash distribution, floating rate base |  |  |  |  |  | three-month LIBOR |  |  |
Term note |  |  |  |  |  |  |  |  |
Junior subordinated debentures |  |  |  |  |  |  |  |  |
Proceeds from term note |  | $ 20,000,000 | $ 20,000,000.0 |  |  |  |  |  |
Junior Subordinated Debt |  |  |  |  |  |  |  |  |
Junior subordinated debentures |  |  |  |  |  |  |  |  |
Junior Subordinated Debentures issuance cost | $ 1,000 |  |  |  |  | $ 1,000 |  | $ 644,000 |
Junior Subordinated Debt | Old Second Capital Trust I |  |  |  |  |  |  |  |  |
Junior subordinated debentures |  |  |  |  |  |  |  |  |
Cash distribution rate of trust preferred securities (as a percent) |  | 7.80% |  |  |  |  |  |  |
Junior subordinated debentures |  | $ 32,600,000 |  |  |  |  |  |  |
Amortization period |  | 30 years |  |  |  |  |  |  |
Redemption price per share |  | $ 10.13 |  |  |  |  |  |  |
Proceeds from term note |  | $ 33,000,000.0 |  |  |  |  |  |  |
Unamortized debt issuance costs |  | $ 635,000 |  |  |  |  |  |  |
Junior Subordinated Debt | Old Second Capital Trust II [Member] |  |  |  |  |  |  |  |  |
Junior subordinated debentures |  |  |  |  |  |  |  |  |
Junior subordinated debentures | $ 25,800,000 |  |  |  |  | $ 25,800,000 |  |  |

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- Definition The reference rate for the variable rate of the trust preferred securities, such as LIBOR or the US treasury rate and the maturity of the reference rate used, such as three months or six months LIBOR. + References No definition available. + Details
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- Definition Amount, after accumulated amortization, of debt issuance costs. Includes, but is not limited to, legal, accounting, underwriting, printing, and registration costs. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02.17) -URI http://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 835 -SubTopic 30 -Section 45 -Paragraph 3 -URI http://asc.fasb.org/extlink&oid=119993939&loc=d3e28555-108399 + Details
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- Definition Including the current and noncurrent portions, the carrying value of junior subordinated long-term debt owed to unconsolidated subsidiary trusts as of the balance sheet date. Such debt places a lender in a lien position behind debt having a higher priority of repayment in liquidation of the entity's assets and was initially scheduled to be repaid after one year or beyond the normal operating cycle if longer. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 210 -Section S99 -Paragraph 1 -Subparagraph (SX 210.7-03.16) -URI http://asc.fasb.org/extlink&oid=120400017&loc=d3e572229-122910 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 210 -Section S99 -Paragraph 1 -Subparagraph (SX 210.9-03.16) -URI http://asc.fasb.org/extlink&oid=120398452&loc=d3e534808-122878 + Details
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- Definition The price per share at which the preferred stock of an entity that has priority over common stock in the distribution of dividends and in the event of liquidation of the entity is redeemed or may be called at. The redemption features of this preferred stock are solely within the control of the issuer. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 505 -SubTopic 10 -Section 50 -Paragraph 5 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=109259400&loc=d3e21488-112644 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 505 -SubTopic 10 -Section 50 -Paragraph 3 -URI http://asc.fasb.org/extlink&oid=109259400&loc=d3e21475-112644 Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 505 -SubTopic 10 -Section 50 -Paragraph 11 -URI http://asc.fasb.org/extlink&oid=109259400&loc=d3e21564-112644 + Details
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- Definition The cash inflow from issuance of preferred stocks by a business trust or other special purpose entity, mainly established by a bank holding entity, to third party investors. The trust's assets are deeply subordinated debentures of the bank holding entity. Most trust preferred securities are subject to a mandatory redemption upon the repayment of the debentures. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 45 -Paragraph 14 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=121586364&loc=d3e3255-108585 + Details
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