Note 6 - Investments in Marketable Securities (Details Textual) - USD ($)	3 Months Ended
Dec. 31, 2019	Dec. 31, 2018	Sep. 30, 2019
Marketable Securities, Accumulated Unrealized Gain (Loss)	$ 160,223,000		$ 140,692,000
Marketable Securities, Unrealized Gain (Loss), Total	$ 19,531,000	$ (28,640,000)

Amount of unrealized gain (loss) on investment in marketable security.

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)(c))
-URI http://asc.fasb.org/extlink&oid=116634182&loc=SL114868664-224227

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Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration