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Note 3 - Investment Securities (Details Textual) - USD ($) | 12 Months Ended
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Dec. 31, 2017 | Dec. 31, 2016 | Dec. 31, 2015
Securities Continuous Unrealized Loss Position, Fair Value | $ 1,400,000,000 | $ 1,200,000,000 |
Securities Continuous Unrealized Loss Position Fair Value Percent of Portfolio | 73.50% | 75.70% |
Available-for-sale Securities Pledged as Collateral | $ 1,200,000,000 | $ 915,200,000 |
Available-for-sale Securities, Gross Realized Gains | 2,400,000 | 5,800,000 | $ 350,000
Available-for-sale Securities, Gross Realized Losses | $ 1,300,000 | $ 0 | $ 43,000
Income Tax Benefit Related to Security Gains (Losses) Percentage | 39.225% |  |

X
- Definition Represents the tax expense/benefit related to security gains/losses as a percentage of the gross amounts. + References No definition available. + Details
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X
- Definition Unrealized loss position which are categorized as held-to-maturity or available-for-sale. + References No definition available. + Details
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X
- Definition This item represents the aggregate fair value of investments in debt and equity securities in an unrealized loss position which are categorized as held-to-maturity or available-for-sale as a percentage of the total held-to-maturity and available-for-sale investment portfolio. + References No definition available. + Details
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- Definition This item represents the gross profit realized on the sale of debt or equity securities categorized neither as held-to-maturity nor trading securities. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 9 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=82897076&loc=d3e27357-111563 + Details
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- Definition This item represents the gross loss realized on the sale of debt or equity securities categorized neither as held-to-maturity nor trading securities. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 9 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=82897076&loc=d3e27357-111563 + Details
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- Definition The fair value of available-for-sale securities that serve as collateral for borrowings. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 310 -SubTopic 10 -Section 50 -Paragraph 5 -URI http://asc.fasb.org/extlink&oid=84173941&loc=d3e5086-111524 + Details
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