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Note 3 - Investment Securities Available for Sale - Gross Unrealized Losses and Fair Value (Details) - USD ($) $ in Thousands | Dec. 31, 2017 | Dec. 31, 2016
--- | --- | ---
Less than Twelve Months, Fair Value | $ 7,264 | $ 36,925
Less than Twelve Months, Gross Unrealized Losses | (81) | (699)
Twelve Months or Greater, Fair Value | 15,554 | 5,754
Twelve Months or Greater, Gross Unrealized Losses | (315) | (184)
Total, Fair Value | 22,818 | 42,679
Total, Gross Unrealized Losses | (396) | (883)
US Government Agencies Debt Securities [Member] |  |
Less than Twelve Months, Fair Value | 557 | 3,803
Less than Twelve Months, Gross Unrealized Losses | (4) | (47)
Twelve Months or Greater, Fair Value | 4,036 | 1,316
Twelve Months or Greater, Gross Unrealized Losses | (67) | (49)
Total, Fair Value | 4,593 | 5,119
Total, Gross Unrealized Losses | (71) | (96)
US States and Political Subdivisions Debt Securities [Member] | Tax Exempt [Member] |  |
Less than Twelve Months, Fair Value | 1,009 | 23,554
Less than Twelve Months, Gross Unrealized Losses | (6) | (522)
Twelve Months or Greater, Fair Value | 2,784 | 0
Twelve Months or Greater, Gross Unrealized Losses | (32) |
Total, Fair Value | 3,793 | 23,554
Total, Gross Unrealized Losses | (38) | (522)
US States and Political Subdivisions Debt Securities [Member] | Taxable [Member] |  |
Less than Twelve Months, Fair Value |  | 502
Less than Twelve Months, Gross Unrealized Losses |  | (4)
Twelve Months or Greater, Fair Value |  |
Twelve Months or Greater, Gross Unrealized Losses |  |
Total, Fair Value |  | 502
Total, Gross Unrealized Losses |  | (4)
Mortgage-backed Securities, Issued by US Government Sponsored Enterprises [Member] |  |
Less than Twelve Months, Fair Value | 5,698 | 9,066
Less than Twelve Months, Gross Unrealized Losses | (71) | (126)
Twelve Months or Greater, Fair Value | 8,734 | 4,438
Twelve Months or Greater, Gross Unrealized Losses | (216) | (135)
Total, Fair Value | 14,432 | 13,504
Total, Gross Unrealized Losses | $ (287) | $ (261)

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- Definition Amount of accumulated unrealized loss on investments in debt and equity securities classified as available-for-sale that have been in a continuous loss position for twelve months or longer. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 6 -Subparagraph (a)(2) -URI http://asc.fasb.org/extlink&oid=82897076&loc=d3e27290-111563 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 7 -URI http://asc.fasb.org/extlink&oid=82897076&loc=d3e27337-111563 + Details
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