Note 5 - Marketable Securities (Tables)

12 Months Ended

Sep. 30, 2024

Notes Tables

Schedule of Available-for-Sale Securities Reconciliation [Table Text Block]

			Gross			Gross
	Amortized		Unrealized			Unrealized
	Cost		Losses			Gains		Fair Value
September 30, 2024:
U.S. Treasury securities and obligations of U.S. government agencies	$	118,159	$	(119	)	$	51	$	118,091
Bank certificates of deposits		5,212		(13	)		1		5,200
Corporate securities		77,580		(255	)		—		77,325
	$	200,951	$	(387	)	$	52	$	200,616
September 30, 2023:
U.S. Treasury securities and obligations of U.S. government agencies	$	227,804	$	(2,573	)	$	—	$	225,231
Bank certificates of deposits		8,122		(170	)		—		7,952
Corporate securities		221,155		(4,127	)		—		217,028
	$	457,081	$	(6,870	)	$	—	$	450,211

Investments Classified by Contractual Maturity Date [Table Text Block]

	Amortized
	Cost		Fair Value
Due in one year or less	$	151,510	$	151,162
Due after one year through five years		45,654		45,667
Due after five years through ten years		—		—
Due after ten years		3,787		3,787
Total marketable securities	$	200,951	$	200,616