Note 2 - Summary of Significant Accounting Policies - Investment in Financial Instruments (Details) - USD ($)	12 Months Ended
Sep. 30, 2022	Sep. 30, 2021
Marketable securities, fair value	$ 275,529,000	$ 347,573,000
Marketable securities, gross unrealized gains	120,692,000	244,093,000
Common Stock [Member]
Marketable securities, fair value	275,529,000	347,573,000
Marketable securities, amortized cost	154,837,000	103,480,000
Marketable securities, gross unrealized gains	$ 120,692,000	$ 244,093,000

Amount of investment in equity security measured at fair value with change in fair value recognized in net income (FV-NI), classified as current.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02(2))
-URI https://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682

Reference 2: http://www.xbrl.org/2003/role/exampleRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section 45
-Paragraph 1
-Subparagraph (f)
-URI https://asc.fasb.org/extlink&oid=124098289&loc=d3e6676-107765

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 825
-SubTopic 10
-Section 45
-Paragraph 1A
-URI https://asc.fasb.org/extlink&oid=123594786&loc=SL75136599-209740

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Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant