Note 12 - Stock-based Compensation - Summary of Information Related to Options Outstanding (Details) - $ / shares	12 Months Ended
Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Mercantile Plans [Member]
Minimum exercise price (in dollars per share)	$ 22.15	$ 22.15	$ 22.15
Maximum exercise price (in dollars per share)	$ 36.22	$ 36.22	$ 36.22
Average remaining option term (Year)	3 years 146 days	4 years 36 days	5 years
First Bank Plans [Member]
Minimum exercise price (in dollars per share)	$ 5.19	$ 5.19	$ 5.19
Maximum exercise price (in dollars per share)	$ 5.19	$ 8.60	$ 8.60
Average remaining option term (Year)	328 days	1 year 182 days	1 year 255 days

The floor of a customized range of exercise prices for purposes of disclosing shares potentially issuable under outstanding stock option awards on all stock option plans and other required information pertaining to awards in the customized range.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (g)
-URI http://asc.fasb.org/extlink&oid=116856206&loc=d3e5070-113901

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- Definition

The ceiling of a customized range of exercise prices for purposes of disclosing shares potentially issuable under outstanding stock option awards on all stock option plans and other required information pertaining to awards in the customized range.

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- Definition

Weighted average remaining contractual term of outstanding stock options, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
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-URI http://asc.fasb.org/extlink&oid=116856206&loc=d3e5070-113901

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