Note 5 - Marketable Securities - Reconciliation of Marketable Securities (Details) - USD ($) $ in Thousands	Sep. 30, 2024	Sep. 30, 2023
Amortized cost	$ 200,951	$ 457,081
Gross unrealized losses	(387)	(6,870)
Gross unrealized gains	52	0
Available-for-sale debt securities	200,616	450,211
US Treasury and Government [Member]
Amortized cost	118,159	227,804
Gross unrealized losses	(119)	(2,573)
Gross unrealized gains	51	0
Available-for-sale debt securities	118,091	225,231
Certificates of Deposit [Member]
Amortized cost	5,212	8,122
Gross unrealized losses	(13)	(170)
Gross unrealized gains	1	0
Available-for-sale debt securities	5,200	7,952
Corporate Debt Securities [Member]
Amortized cost	77,580	221,155
Gross unrealized losses	(255)	(4,127)
Gross unrealized gains	0	0
Available-for-sale debt securities	$ 77,325	$ 217,028