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Note 18 - Variable Interest Entities (Details Textual) $ in Thousands |  |  | 12 Months Ended |
--- | --- | --- | --- | ---
Jan. 26, 2016 USD ($) | Jun. 01, 2014 USD ($) | Dec. 31, 2023 USD ($) | Dec. 31, 2022 USD ($)
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 |  |
Amortization of Fair Value Discount Related to Subordinated Debentures of Assumed Business Trusts |  | $ 700 |  |
Amortization Period of Fair Value Discount Related to Subordinated Debentures of Assumed Business Trusts (Year) |  | 21 years 6 months |  |
Preferred Securities of Subsidiary Trust |  |  | $ 47,600 | $ 46,900
Junior Subordinated Debenture Owed to Unconsolidated Subsidiary Trust, Total |  |  | 49,644 | 48,958
Other Assets [Member] |  |  |  |
Low-Income Housing Tax Credit and Historic Tax Credits, Investment |  |  | 25,700 | 3,200
Other Liabilities [Member] |  |  |  |
Low-Income Housing Tax Credit and Historic Tax Credits, Commitment |  |  | 21,100 | $ 1,400
Mercantile Bank Capital Trust I [Member] |  |  |  |
Preferred Securities of Subsidiary Trust | $ 32,000 |  | $ 21,000 |
Payments for Repurchase of Trust Preferred Securities | 11,000 |  |  |
Junior Subordinated Debenture Owed to Unconsolidated Subsidiary Trust, Total | 21,000 |  |  |
Fund [Member] | Mercantile Bank Capital Trust I [Member] |  |  |  |
Preferred Securities of Subsidiary Trust | $ 11,000 |  |  |
Five Business Trusts [Member] |  |  |  |
Variable Interest Entity, Qualitative or Quantitative Information, Ownership Percentage |  |  | 100.00% |

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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 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 Amount of commitment or contingent commitments to low-income housing tax credit and historic tax credit. + 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://www.xbrl.org/2009/role/commonPracticeRef -Topic 944 -SubTopic 210 -Name Accounting Standards Codification -Section S99 -Paragraph 1 -Subparagraph (SX 210.7-03(a)(16)(a)(2)) -Publisher FASB -URI https://asc.fasb.org//1943274/2147479440/944-210-S99-1 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Name Accounting Standards Codification -Topic 942 -SubTopic 210 -Section S99 -Paragraph 1 -Subparagraph (SX 210.9-03.16) -Publisher FASB -URI https://asc.fasb.org//1943274/2147479853/942-210-S99-1 + Details
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