Note 12 - Stock-based Compensation - Summary of Stock Option Grants and Exercises (Details) - USD ($)	12 Months Ended
Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Proceeds from stock option exercises, net of cashless exercises	$ 108,000	$ 318,000	$ 978,000
Mercantile Plans [Member]
Aggregate intrinsic value of stock options exercised	17,000	15,000	6,000
Proceeds from stock option exercises, net of cashless exercises	33,000	0	22,000
Tax benefit realized from stock option exercises	0	0	$ 0
Weighted average per share fair value of stock options granted (in dollars per share)			$ 5.25
First Bank Plans [Member]
Aggregate intrinsic value of stock options exercised	300,000	594,000	$ 1,945,000
Proceeds from stock option exercises, net of cashless exercises	108,000	318,000	956,000
Tax benefit realized from stock option exercises	$ 0	$ 208,000	$ 681,000
Weighted average per share fair value of stock options granted (in dollars per share)	$ 0	$ 0	$ 0

Amount of tax benefit from exercise of stock options granted under share-based compensation arrangement.

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Amount of cash inflow from exercise of stock options granted under share-based compensation arrangement.

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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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-Publisher FASB
-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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