Note 4 - Marketable Securities - Reconciliation of Marketable Securities (Details) - USD ($) $ in Thousands	Mar. 31, 2025	Sep. 30, 2024
Amortized cost	$ 251,441	$ 200,951
Gross unrealized losses	(132)	(387)
Gross unrealized gains	169	52
Fair value	251,478	200,616
US Treasury and Government [Member]
Amortized cost	214,926	118,159
Gross unrealized losses	(99)	(119)
Gross unrealized gains	132	51
Fair value	214,959	118,091
Certificates of Deposit [Member]
Amortized cost	1,975	5,212
Gross unrealized losses	(2)	(13)
Gross unrealized gains	0	1
Fair value	1,973	5,200
Corporate Debt Securities [Member]
Amortized cost	25,254	77,580
Gross unrealized losses	(31)	(255)
Gross unrealized gains	0	0
Fair value	25,223	$ 77,325
US States and Political Subdivisions Debt Securities [Member]
Amortized cost	9,286
Gross unrealized losses	0
Gross unrealized gains	37
Fair value	$ 9,323