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Note 2 - Summary of Significant Accounting Policies - Investment in Financial Instruments (Details) - USD ($) | 12 Months Ended
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Sep. 30, 2020 | Sep. 30, 2019
Marketable securities, fair value | $ 179,368,000 | $ 194,581,000
Marketable securities, gross unrealized gains | 137,593,000 | 140,692,000
Common Stock [Member] |  |
Marketable securities, fair value | 179,368,000 | 194,581,000
Marketable securities, amortized cost | 41,775,000 | 53,889,000
Marketable securities, gross unrealized gains | $ 137,593,000 | $ 140,692,000

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- Definition Amount of investment in equity security measured at fair value with change in fair value recognized in net income (FV-NI). + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 825 -SubTopic 10 -Section 45 -Paragraph 1A -URI http://asc.fasb.org/extlink&oid=99377092&loc=SL75136599-209740 + Details
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- Definition Cost of investment in equity security measured at fair value with change in fair value recognized in net income (FV-NI). Excludes equity method investment and investment in equity security without readily determinable fair value. + References No definition available. + Details
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- Definition Amount of unrealized gain (loss) on investment in equity security measured at fair value with change in fair value recognized in net income (FV-NI). + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 220 -Section S99 -Paragraph 1 -Subparagraph (SX 210.7-04(3)(d)) -URI http://asc.fasb.org/extlink&oid=120400993&loc=SL114874131-224263 Reference 2: http://www.xbrl.org/2009/role/commonPracticeRef -Publisher FASB -Name Accounting Standards Codification -Topic 321 -SubTopic 10 -Section 50 -Paragraph 4 -URI http://asc.fasb.org/extlink&oid=120269885&loc=SL75117546-209714 + Details
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