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Note 1 - Summary of Significant Accounting Policies (Details) | 12 Months Ended |  |
--- | --- | --- | ---
Dec. 31, 2015 USD ($) | Dec. 31, 2014 USD ($) | Jun. 01, 2014 USD ($)
Note 1 - Summary of Significant Accounting Policies (Details) [Line Items] |  |  |
Number of Unconsolidated Business Trusts Formed to Issue Trust Preferred Securities | 5 |  |
Number of Operating Segments | 1 |  |
Loans and Leases Receivable, Deferred Income | $ 1,400,000 | $ 1,100,000 |
Interest Income on Commercial and Mortgage Loans, Discontinued Period | 90 days |  |
Maximum Delinquency Period for Consumer and Credit Card Loans to be Charged-off | 120 days |  |
Repossessed Assets | $ 1,300,000 | $ 2,000,000 |
Firstbank Corporation [Member] |  |  |
Note 1 - Summary of Significant Accounting Policies (Details) [Line Items] |  |  |
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Assets | $ 1,500,000,000 |  | $ 1,452,880,000
Business Combination, Branches Acquired | 46 |  | 46
Core Deposits [Member] |  |  |
Note 1 - Summary of Significant Accounting Policies (Details) [Line Items] |  |  |
Acquired Finite-lived Intangible Assets, Weighted Average Useful Life | 10 years |  |
Minimum [Member] | Building Improvements [Member] |  |  |
Note 1 - Summary of Significant Accounting Policies (Details) [Line Items] |  |  |
Property, Plant and Equipment, Useful Life | 5 years |  |
Minimum [Member] | Furniture and Fixtures [Member] |  |  |
Note 1 - Summary of Significant Accounting Policies (Details) [Line Items] |  |  |
Property, Plant and Equipment, Useful Life | 3 years |  |
Maximum [Member] | Building Improvements [Member] |  |  |
Note 1 - Summary of Significant Accounting Policies (Details) [Line Items] |  |  |
Property, Plant and Equipment, Useful Life | 33 years |  |
Maximum [Member] | Furniture and Fixtures [Member] |  |  |
Note 1 - Summary of Significant Accounting Policies (Details) [Line Items] |  |  |
Property, Plant and Equipment, Useful Life | 7 years |  |

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