Note 4 - Marketable Securities (Tables)

6 Months Ended

Mar. 31, 2025

Notes Tables

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

			Gross			Gross
	Amortized		Unrealized			Unrealized
	Cost		Losses			Gains		Fair Value
March 31, 2025:
U.S. Treasury securities and obligations of U.S. government agencies	$	214,926	$	(99	)	$	132	$	214,959
Bank certificates of deposit		1,975		(2	)		—		1,973
Corporate securities		25,254		(31	)		—		25,223
Municipal securities		9,286		—			37		9,323
	$	251,441	$	(132	)	$	169	$	251,478
September 30, 2024:
U.S. Treasury securities and obligations of U.S. government agencies	$	118,159	$	(119	)	$	51	$	118,091
Bank certificates of deposit		5,212		(13	)		1		5,200
Corporate securities		77,580		(255	)		—		77,325
	$	200,951	$	(387	)	$	52	$	200,616

Investments Classified by Contractual Maturity Date [Table Text Block]

	Amortized
	Cost		Fair Value
Due in one year or less	$	74,754	$	74,697
Due after one year through five years		173,099		173,193
Due after ten years		3,588		3,588
Total marketable securities	$	251,441	$	251,478