Note 11 - Stock-based Compensation - Summary of Restricted Stock Activity (Details) - Restricted Stock [Member] - Mercantile Plans [Member] - $ / shares	12 Months Ended
Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Nonvested at beginning of year (in shares)	353,691	262,336	262,260
Nonvested at beginning of year (in dollars per share)	$ 30.71	$ 29.42	$ 34.91
Granted (in shares)	121,631	163,000	121,518
Granted (in dollars per share)	$ 32.18	$ 33.68	$ 24.65
Vested (in shares)	(94,010)	(59,772)	(85,445)
Vested (in dollars per share)	$ 34.86	$ 31.82	$ 37.08
Forfeited (in shares)	(6,541)	(11,873)	(35,997)
Forfeited (in dollars per share)	$ 27.98	$ 29.54	$ 33.71
Nonvested at end of year (in shares)	374,771	353,691	262,336
Nonvested at end of year (in dollars per share)	$ 30.49	$ 30.71	$ 29.42

The number of equity-based payment instruments, excluding stock (or unit) options, that were forfeited during the reporting period.

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Weighted average fair value as of the grant date of equity-based award plans other than stock (unit) option plans that were not exercised or put into effect as a result of the occurrence of a terminating event.

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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 weighted average fair value at grant date for nonvested equity-based awards issued 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 number of non-vested equity-based payment instruments, excluding stock (or unit) options, that validly exist and are outstanding as of the balance sheet date.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (c)(2)(ii)
-URI https://asc.fasb.org/extlink&oid=128089324&loc=d3e5070-113901

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (c)(2)(i)
-URI https://asc.fasb.org/extlink&oid=128089324&loc=d3e5070-113901

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Per share or unit weighted-average fair value of nonvested award under share-based payment arrangement. Excludes share and unit options.

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Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (c)(2)(i)
-URI https://asc.fasb.org/extlink&oid=128089324&loc=d3e5070-113901

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-Publisher FASB
-Name Accounting Standards Codification
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-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (c)(2)(ii)
-URI https://asc.fasb.org/extlink&oid=128089324&loc=d3e5070-113901

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The number of equity-based payment instruments, excluding stock (or unit) options, that vested during the reporting period.

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The weighted average fair value as of grant date pertaining to an equity-based award plan other than a stock (or unit) option plan for which the grantee gained the right during the reporting period, by satisfying service and performance requirements, to receive or retain shares or units, other instruments, or cash in accordance with the terms of the arrangement.

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