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Note 3 - Investment Securities - Income Earned on Securities (Details) - USD ($) $ in Thousands | 12 Months Ended
--- | ---
Dec. 31, 2017 | Dec. 31, 2016 | Dec. 31, 2015
Non-taxable |  |  |
Total | $ 40,115 | $ 33,479 | $ 30,613
Held-to-maturity Securities [Member] |  |  |
Taxable |  |  |
Taxable | 2,521 | 3,778 | 5,162
Non-taxable |  |  |
Non-taxable | 8,693 | 10,641 | 11,635
Available-for-sale Securities [Member] |  |  |
Taxable |  |  |
Taxable | 25,996 | 17,928 | 12,129
Non-taxable |  |  |
Non-taxable | $ 2,905 | $ 1,132 | $ 1,687

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- Definition Amount of operating interest income, including amortization and accretion of premiums and discounts, on securities exempt from state, federal and other income tax. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 225 -Section S99 -Paragraph 1 -Subparagraph (SX 210.9-04.2) -URI http://asc.fasb.org/extlink&oid=6879574&loc=d3e536633-122882 + Details
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