Note 6 - Investments in Marketable Securities (Details Textual) - USD ($)	3 Months Ended		9 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019	Sep. 30, 2019
Marketable Securities, Accumulated Unrealized Gain (Loss)	$ 99,501,000		$ 99,501,000		$ 140,692,000
Marketable Securities, Unrealized Gain (Loss), Total	$ 16,489,000	$ 3,214,000	$ (41,191,000)	$ (16,929,000)