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Note 20 - Subordinated Debentures (Details) - Business Trusts - USD ($) $ in Thousands | 12 Months Ended |
--- | --- | ---
Dec. 31, 2015 | Dec. 31, 2014
Subordinated Borrowing [Line Items] |  |
Preferred securities outstanding | $ 53,100 | $ 52,400
Mercantile Bank Capital Trust I [Member] |  |
Subordinated Borrowing [Line Items] |  |
Preferred securities outstanding | $ 32,000,000 |
Mercantile Bank Capital Trust I [Member] | London Interbank Offered Rate (LIBOR) [Member] |  |
Subordinated Borrowing [Line Items] |  |
Interest Rate Margin | 2.18% |
Firstbank Capital Trust I [Member] |  |
Subordinated Borrowing [Line Items] |  |
Preferred securities outstanding | $ 10,000,000 |
Firstbank Capital Trust I [Member] | London Interbank Offered Rate (LIBOR) [Member] |  |
Subordinated Borrowing [Line Items] |  |
Interest Rate Margin | 1.99% |
Firstbank Capital Trust II [Member] |  |
Subordinated Borrowing [Line Items] |  |
Preferred securities outstanding | $ 10,000,000 |
Firstbank Capital Trust II [Member] | London Interbank Offered Rate (LIBOR) [Member] |  |
Subordinated Borrowing [Line Items] |  |
Interest Rate Margin | 1.27% |
Firstbank Capital Trust III [Member] |  |
Subordinated Borrowing [Line Items] |  |
Preferred securities outstanding | $ 7,500,000 |
Firstbank Capital Trust III [Member] | London Interbank Offered Rate (LIBOR) [Member] |  |
Subordinated Borrowing [Line Items] |  |
Interest Rate Margin | 1.35% |
Firstbank Capital Trust IV [Member] |  |
Subordinated Borrowing [Line Items] |  |
Preferred securities outstanding | $ 7,500,000 |
Firstbank Capital Trust IV [Member] | London Interbank Offered Rate (LIBOR) [Member] |  |
Subordinated Borrowing [Line Items] |  |
Interest Rate Margin | 1.35% |

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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 Percentage points added to the reference rate to compute the variable rate on the debt instrument. + References No definition available. + Details
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- Definition Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table. + References No definition available. + Details
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- Details
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- Details
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- Details
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- Details
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- Details
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- Details
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