Note 4 - Marketable Securities - Reconciliation of Marketable Securities (Details) - USD ($) $ in Thousands	Dec. 31, 2024	Sep. 30, 2024
Amortized cost	$ 113,580	$ 200,951
Gross unrealized losses	(205)	(387)
Gross unrealized gains	9	52
Fair value	113,384	200,616
US Treasury and Government [Member]
Amortized cost	68,189	118,159
Gross unrealized losses	(83)	(119)
Gross unrealized gains	9	51
Fair value	68,115	118,091
Certificates of Deposit [Member]
Amortized cost	2,229	5,212
Gross unrealized losses	(6)	(13)
Gross unrealized gains	0	1
Fair value	2,223	5,200
Corporate Debt Securities [Member]
Amortized cost	42,634	77,580
Gross unrealized losses	(116)	(255)
Gross unrealized gains	0	0
Fair value	42,518	$ 77,325
US States and Political Subdivisions Debt Securities [Member]
Amortized cost	528
Gross unrealized losses	0
Gross unrealized gains	0
Fair value	$ 528