Note 4 - Marketable Securities (Tables)

9 Months Ended

Jun. 30, 2024

Notes Tables

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

			Gross			Gross
	Amortized		Unrealized			Unrealized
	Cost		Losses			Gains		Fair Value
June 30, 2024:
U.S. Treasury securities and obligations of U.S. government agencies	$	298,843	$	(786	)	$	—	$	298,057
Bank certificates of deposit		5,422		(44	)		—		5,378
Corporate securities		103,869		(941	)		—		102,928
Municipal securities		1,019		—			—		1,019
	$	409,153	$	(1,771	)	$	—	$	407,382
September 30, 2023:
U.S. Treasury securities and obligations of U.S. government agencies	$	227,804	$	(2,573	)	$	—	$	225,231
Bank certificates of deposit		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	$	260,690	$	259,296
Due after one year through five years		144,955		144,578
Due after five years through ten years		—		—
Due after ten years		3,508		3,508
Total marketable securities	$	409,153	$	407,382