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Note 12 - Stock-based Compensation (Details) - Summary of Stock Option Grants and Exercises - USD ($)	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Note 12 - Stock-based Compensation (Details) - Summary of Stock Option Grants and Exercises [Line Items]
Cash received from stock option exercises	$ 891,000	$ 282,000	$ 289,000
Mercantile Plans [Member]
Note 12 - Stock-based Compensation (Details) - Summary of Stock Option Grants and Exercises [Line Items]
Aggregate intrinsic value of stock options exercised	36,000	11,000	408,000
Cash received from stock option exercises	17,000	50,000	289,000
Tax benefit realized from stock option exercises	$ 0	$ 0	$ 0
Weighted average per share fair value of stock options granted (in Dollars per share)	$ 4.41	$ 2.72
Firstbank Plans [Member]
Note 12 - Stock-based Compensation (Details) - Summary of Stock Option Grants and Exercises [Line Items]
Aggregate intrinsic value of stock options exercised	$ 420,000	$ 333,000
Cash received from stock option exercises	874,000	232,000
Tax benefit realized from stock option exercises	$ 147,000	$ 116,000
Weighted average per share fair value of stock options granted (in Dollars per share)

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Disclosure of the aggregate tax benefit realized from the exercise of stock options and the conversion of similar instruments during the annual period.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (j)
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The cash inflow associated with the amount received from holders exercising their stock options. This item inherently excludes any excess tax benefit, which the entity may have realized and reported separately.

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Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
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-Topic 718
-SubTopic 10
-Section 50
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Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Glossary Financing Activities
-URI http://asc.fasb.org/extlink&oid=6513228

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Amount of accumulated difference between fair value of underlying shares on dates of exercise and exercise price on options exercised (or share units converted) into shares.

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-Name Accounting Standards Codification
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The weighted average grant-date fair value of options granted during the reporting period as calculated by applying the disclosed option pricing methodology.

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