Represents the benchmark for the maximum number of shares awarded required for maximum vesting rights.

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Represents the benchmark for the minimum number of shares awarded required for minimum vesting rights.

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No definition available.

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Represents the expense recognized during the period arising from equity-based compensation arrangements (for example, shares of stock, unit, stock options or other equity instruments) with employees, directors and certain consultants qualifying for treatment as employees.

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Weighted average period over which unrecognized compensation is expected to be recognized for equity-based compensation plans, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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- Definition

Unrecognized cost of unvested share-based awards, other than options, awarded to employees as compensation.

+ References

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Period which an employee's right to exercise an award is no longer contingent on satisfaction of either a service condition, market condition or a performance condition, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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The number of grants made during the period on other than stock (or unit) option plans (for example, phantom stock or unit plan, stock or unit appreciation rights plan, performance target plan).

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The maximum number of shares (or other type of equity) originally approved (usually by shareholders and board of directors), net of any subsequent amendments and adjustments, for awards under the equity-based compensation plan. As stock or unit options and equity instruments other than options are awarded to participants, the shares or units remain authorized and become reserved for issuance under outstanding awards (not necessarily vested).

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Gross number of share options (or share units) granted during the period.

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No definition available.

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Percentage of vesting of share-based compensation awards.

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Period from grant date that an equity-based award expires, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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Amount of difference between fair value of the underlying shares reserved for issuance and exercise price of vested portions of options outstanding and currently exercisable.

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Number of options vested.

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Purchase price of common stock expressed as a percentage of its fair value.

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No definition available.

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Number of shares issued in lieu of cash for services contributed to the entity. Number of shares includes, but is not limited to, shares issued for services contributed by vendors and founders.

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No definition available.

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Note 12 - Stock-based Compensation (Details Textual) - USD ($) $ in Millions							12 Months Ended
	Oct. 25, 2018	May 24, 2018	May 25, 2017	Jun. 06, 2016	May 28, 2015	Jun. 01, 2014	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Authorized							197,000
Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Gross							0	0
Mercantile Plans [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Gross							0	0	6,500
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercisable, Intrinsic Value							$ 0.1
First Bank Plans [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Gross							0	0	0
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercisable, Intrinsic Value							$ 0.1
Firstbank Corporation [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Gross						282,200
Share-based Compensation Arrangement by Share-based Payment Award, Options, Vested, Number of Shares						258,400				23,800
First Bank Employees [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Expiration Period							10 years
Share-based Compensation Arrangement by Share-based Payment Award, Maximum Number of Shares for Maximum Vesting Rights							50
Share-based Compensation Arrangement by Share-based Payment Award, Minimum Number of Shares for Minimum Vesting Rights							50
First Bank Employees [Member] \| Grant Per Annum Starting One Year From Date of Grant [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Rights, Percentage							20.00%
First Bank Employees [Member] \| Minimum [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Period							1 year
First Bank Employees [Member] \| Maximum [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Period							5 years
Director [Member]
Stock Issued During Period, Shares, Issued for Services		11,000	12,000	13,000	14,000
Allocated Share-based Compensation Expense, Total		$ 0.4	$ 0.4	$ 0.3	$ 0.3
Bank Board Members [Member]
Stock Issued During Period, Shares, Issued for Services	1,000
Allocated Share-based Compensation Expense, Total	$ 0.1
Restricted Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Period							3 years	3 years	3 years	3 years	3 years
Employee Service Share-based Compensation, Nonvested Awards, Compensation Not yet Recognized, Share-based Awards Other than Options							$ 5.8
Employee Service Share-based Compensation, Nonvested Awards, Compensation Cost Not yet Recognized, Period for Recognition							3 years
Restricted Stock [Member] \| Mercantile Plans [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period							91,400	94,592	86,250
Employee Stock Option [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Period									2 years	2 years	2 years
Share-based Compensation Arrangement by Share-based Payment Award, Purchase Price of Common Stock, Percent									110.00%	110.00%	110.00%
Share-based Compensation Arrangement by Share-based Payment Award, Expiration Period									7 years	7 years	7 years
Performance Shares [Member] \| Executive Officer [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period							24,633