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Note 14 - Financial Highlights (Details Textual) - Horizon Technology Finance Management LLC (the Advisor) [Member] - Investment Management Agreement [Member] - USD ($) $ in Millions | 12 Months Ended
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Dec. 31, 2019 | Dec. 31, 2018 | Dec. 31, 2017 | Dec. 31, 2015
Management Service, Incentive [Member] |  |  |  |
Investment Company, Voluntary Fee Waived | $ 1.8 | $ 1.2 | $ 0.1 |
Management Service, Base [Member] |  |  |  |
Investment Company, Voluntary Fee Waived |  |  |  | $ 0.3

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- Definition Amount of fee voluntarily waived by investment company. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Topic 946 -SubTopic 20 -Name Accounting Standards Codification -Section 50 -Paragraph 7 -Publisher FASB -URI https://asc.fasb.org/1943274/2147480990/946-20-50-7 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Topic 946 -SubTopic 220 -Name Accounting Standards Codification -Section S99 -Paragraph 1 -Subparagraph (SX 210.6-07(2)(a)) -Publisher FASB -URI https://asc.fasb.org/1943274/2147479134/946-220-S99-1 + Details
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