Marketable Securities (Tables)

6 Months Ended

Mar. 31, 2023

Investments, Debt and Equity Securities [Abstract]

Summary of Amortized Cost and Fair Value, Including Accrued Interest Receivable and Unrealized Holding Gains (Losses) on Short-term and Long-term Marketable Securities

			Gross		Gross
	Amortized		Unrealized		Unrealized
	Cost		Losses		Gains		Fair Value
March 31, 2023:
U.S. Treasury securities and obligations of U.S. government agencies	$	435,258	$	(3,672)	$	31	$	431,617
Bank certificates of deposits		10,355		(187)		1		10,169
Corporate securities		341,868		(5,370)		—		336,498
Municipal securities		1,544		(1)		—		1,543
	$	789,025	$	(9,230)	$	32	$	779,827
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

Fair Value of Marketable Securities by Contractual Maturity

	Amortized
	Cost			Fair Value
Due in one year or less	$	515,364	$	513,652
Due after one year through five years		270,591		263,105
Due after five years through ten years		—		—
Due after ten years		3,070		3,070
Total marketable securities	$	789,025	$	779,827