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Note 12 - Stock-based Compensation - Summary of Stock Option Grants and Exercises (Details) - USD ($) | 12 Months Ended
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Dec. 31, 2016 | Dec. 31, 2015 | Dec. 31, 2014
Proceeds from stock option exercises, net of cashless exercises | $ 978,000 | $ 891,000 | $ 282,000
Mercantile Plans [Member] |  |  |
Aggregate intrinsic value of stock options exercised | 6,000 | 36,000 | 11,000
Proceeds from stock option exercises, net of cashless exercises | 22,000 | 17,000 | 50,000
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 | $ 4.41 | $ 2.72
First Bank Plans [Member] |  |  |
Aggregate intrinsic value of stock options exercised | $ 1,945,000 | $ 420,000 | $ 333,000
Proceeds from stock option exercises, net of cashless exercises | 956,000 | 874,000 | 232,000
Tax benefit realized from stock option exercises | $ 681,000 | $ 147,000 | $ 116,000
Weighted average per share fair value of stock options granted (in dollars per share) | $ 0 | $ 0 | $ 0

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- Definition Disclosure of the aggregate tax benefit realized from the exercise of stock options and the conversion of similar instruments during the annual period. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (j) -URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901 + Details
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- Definition The cash inflow associated with the amount received from holders exercising their stock options. This item inherently excludes any excess tax benefit, which the entity may have realized and reported separately. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (j) -URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 45 -Paragraph 14 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=66902209&loc=d3e3255-108585 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Glossary Financing Activities -URI http://asc.fasb.org/extlink&oid=6513228 + Details
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- Definition 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. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (d)(2) -URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901 + Details
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- Definition The weighted average grant-date fair value of options granted during the reporting period as calculated by applying the disclosed option pricing methodology. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (d)(1) -URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901 + Details
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