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Note 4 - Loans and Related Allowance for Loan and Lease Losses - Additional Information on Impaired Loans (Details) - USD ($) $ in Thousands | 12 Months Ended
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Dec. 31, 2017 | Dec. 31, 2016 | Dec. 31, 2015
Average recorded investment | $ 12,836 | $ 13,411 | $ 13,440
Interest income recognized | 715 | 509 | 725
Commercial And Industrial [Member] |  |  |
Average recorded investment | 2,378 | 1,211 | 1,468
Interest income recognized | 178 | 32 | 100
Real Estate Construction Porfolio Segment [Member] |  |  |
Average recorded investment | 565 | 1,281 | 2,407
Interest income recognized | 1 | 10 | 115
Real Estate Mortgage Portfolio Segment [Member] | Residential Loan [Member] |  |  |
Average recorded investment | 3,068 | 3,529 | 4,356
Interest income recognized | 89 | 98 | 160
Real Estate Mortgage Portfolio Segment [Member] | Commercial Loans [Member] |  |  |
Average recorded investment | 6,820 | 7,384 | 5,203
Interest income recognized | 446 | 368 | 350
Consumer Portfolio Segment [Member] |  |  |
Average recorded investment | 5 | 6 | 6
Interest income recognized | $ 1 | $ 1 |

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- Definition Average amount of investment of impaired financing receivables with related allowance for credit losses and without a related allowance for credit losses. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 310 -SubTopic 10 -Section 50 -Paragraph 15 -Subparagraph (c)(1) -URI http://asc.fasb.org/extlink&oid=84173941&loc=d3e5212-111524 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 310 -SubTopic 10 -Section 50 -Paragraph 17 -URI http://asc.fasb.org/extlink&oid=84173941&loc=d3e5258-111524 + Details
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- Definition Amount of interest income recognized that the financing receivables (with related allowance for credit losses and without a related allowance for credit losses) were impaired. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 310 -SubTopic 10 -Section 50 -Paragraph 15 -Subparagraph (c)(2) -URI http://asc.fasb.org/extlink&oid=84173941&loc=d3e5212-111524 + Details
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