Marketable Securities (Tables)

12 Months Ended

Sep. 30, 2023

Investments, Debt and Equity Securities [Abstract]

Summary of amortized cost and fair value

The following is a summary of the amortized cost and the fair value, including accrued interest receivable, as well as unrealized gains (losses) on the short-term and long-term marketable securities as of September 30, 2023 and 2022 (in thousands):

			Gross		Gross
	Amortized		Unrealized		Unrealized
	Cost		Losses		Gains		Fair Value
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
Municipal securities		—		—		—		—
	$	457,081	$	(6,870)	$	—	$	450,211
September 30, 2022:
U.S. Treasury securities and obligations of U.S. government agencies	$	804,774	$	(6,163)	$	21	$	798,632
Bank certificates of deposits		8,335		(158)		1		8,178
Corporate securities		406,270		(8,113)		—		398,157
Municipal securities		59,043		(226)		—		58,817
	$	1,278,422	$	(14,660)	$	22	$	1,263,784

Schedule of fair values of marketable securities by contractual maturities

	Amortized
	Cost			Fair Value
Due in one year or less	$	342,901	$	338,873
Due after one year through five years		111,121		108,279
Due after five years through ten years		—		—
Due after ten years		3,059		3,059
Total marketable securities	$	457,081	$	450,211