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Note 19 - Subordinated Debentures (Details Textual) | Jan. 26, 2016 USD ($) | Jun. 01, 2014 USD ($) | Dec. 31, 2020 USD ($) | Dec. 31, 2019 USD ($)
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Number of Business Trusts |  |  | 5 |
Business Combination Debt Assumed Number of Trusts |  |  | 4 |
Fair Value Discount of Subordinated Debentures Related to Assumed Business Trusts at Time af Merger |  | $ 15,000,000.0 |  |
Amortization of Fair Value Discount Related to Subordinated Debentures of Assumed Business Trusts |  | $ 700,000 |  |
Amortization Period of Fair Value Discount Related to Subordinated Debentures of Assumed Business Trusts (Year) |  | 21 years 6 months |  |
Preferred Securities of Subsidiary Trust |  |  | $ 45,500,000 | $ 44,800,000
Junior Subordinated Debenture Owed to Unconsolidated Subsidiary Trust, Total |  |  | 47,563,000 | $ 46,881,000
Mercantile Bank Capital Trust I [Member] |  |  |  |
Preferred Securities of Subsidiary Trust | $ 32,000,000.0 |  | $ 21,000,000 |
Payments for Repurchase of Trust Preferred Securities | 11,000,000.0 |  |  |
Junior Subordinated Debenture Owed to Unconsolidated Subsidiary Trust, Total | 21,000,000.0 |  |  |
Fund [Member] | Mercantile Bank Capital Trust I [Member] |  |  |  |
Preferred Securities of Subsidiary Trust | $ 11,000,000.0 |  |  |

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- Definition Represents the annual amortization of the fair value discount related to subordinated debentures of assumed business trusts over a period of time. + References No definition available. + Details
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- Definition Represents the amortization period of the fair value discount related to subordinated debentures of assumed business trusts. + References No definition available. + Details
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- Definition The number of trusts for which debt assumed in a business combination are payable to. + References No definition available. + Details
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- Definition Represents the fair value discount of subordinated debentures related to assumed business trusts at the time of the merger. + References No definition available. + Details
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- Definition Represents the Company's business trusts. + References No definition available. + Details
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- Definition Trust preferred securities possesses characteristics of both equity and debt issues and are generally issued by bank holding companies. + References No definition available. + 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 cash outflow to reacquire preferred stocks issued 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 15 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=121586364&loc=d3e3291-108585 + Details
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