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Consolidated Statements of Operations (Parentheticals) - USD ($) $ in Thousands | 12 Months Ended
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Dec. 31, 2020 | Dec. 31, 2019 | Dec. 31, 2018
Income Statement [Abstract] |  |  |
Interest income | $ 264 | $ 745 | $ 1,290

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- Definition Amount before accretion (amortization) of purchase discount (premium) of interest income on nonoperating securities. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 220 -SubTopic 10 -Section S99 -Paragraph 2 -Subparagraph (SX 210.5-03.7(b)) -URI http://asc.fasb.org/extlink&oid=120395209&loc=SL114868664-224227 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 280 -SubTopic 10 -Section 50 -Paragraph 22 -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=120311839&loc=d3e8736-108599 + Details
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