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

No definition available.

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- Definition

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

+ References

No definition available.

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- Definition

Amount of expense for award under share-based payment arrangement. Excludes amount capitalized.

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- Definition

Period over which grantee's right to exercise award under share-based payment arrangement is no longer contingent on satisfaction of service or performance condition, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents reported fact of one year, five months, and thirteen days. Includes, but is not limited to, combination of market, performance or service condition.

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- Definition

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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- Definition

Number of shares authorized for issuance under share-based payment arrangement.

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-Publisher FASB
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- Definition

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

+ References

No definition available.

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- Definition

Percentage of vesting of award under share-based payment arrangement.

+ References

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- Definition

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.

+ References

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- Definition

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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- Definition

Number of options vested.

+ References

No definition available.

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- Definition

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

+ References

No definition available.

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- Definition

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.

+ References

No definition available.

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Note 12 - Stock-based Compensation (Details Textual) - USD ($) $ in Millions							12 Months Ended
	May 23, 2019	Oct. 25, 2018	May 24, 2018	May 25, 2017	Jun. 06, 2016	Jun. 01, 2014	Dec. 31, 2019	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							102,000
Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Gross							0	0	0
Mercantile 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
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	12,000		11,000	12,000	13,000
Share-based Payment Arrangement, Expense			$ 0.4	$ 0.4	$ 0.3		$ 0.4
Bank Board Members [Member]
Stock Issued During Period, Shares, Issued for Services		1,000
Share-based Payment Arrangement, Expense		$ 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	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							84,596	91,400	94,592
Share-based Payment Arrangement, 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							23,596	24,633