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Note 2 - Business Combination (Details Textual) | Jun. 01, 2014 USD ($) shares | Dec. 31, 2016 USD ($) | Dec. 31, 2015 USD ($)
--- | --- | --- | ---
Goodwill |  | $ 49,473,000 | $ 49,473,000
Firstbank Corporation [Member] |  |  |
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Assets | $ 1,500,000,000 |  |
Business Combination Branches Acquired | 46 |  |
Business Acquisition Conversion of Stock Per Share | shares | 1 |  |
Business Acquisition, Equity Interest Issued or Issuable, Number of Shares | shares | 8,087,272 |  |
Goodwill | $ 49,500,000 |  |

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