Marketable Securities (Tables)

6 Months Ended

Mar. 31, 2024

Investments, Debt and Equity Securities [Abstract]

Summary of amortized cost and fair value

			Gross		Gross
	Amortized		Unrealized		Unrealized
	Cost		Losses		Gains		Fair Value
March 31, 2024:
U.S. Treasury securities and obligations of U.S. government agencies	$	433,188	$	(902)	$	8	$	432,294
Bank certificates of deposit		7,870		(68)		—		7,802
Corporate securities		171,648		(1,515)		3		170,136
Municipal securities		1,006		—		—		1,006
	$	613,712	$	(2,485)	$	11	$	611,238
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

Schedule of fair values of marketable securities by contractual maturities

	Amortized
	Cost			Fair Value
Due in one year or less	$	470,012	$	468,220
Due after one year through five years		140,222		139,540
Due after five years through ten years		—		—
Due after ten years		3,478		3,478
Total marketable securities	$	613,712	$	611,238