Marketable Securities (Tables)

9 Months Ended

Jun. 30, 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
June 30, 2023:
U.S. Treasury securities and obligations of U.S. government agencies	$	311,618	$	(3,731)	$	1	$	307,888
Bank certificates of deposits		9,078		(194)		—		8,884
Corporate securities		248,309		(5,186)		—		243,123
Municipal securities		20		(1)		—		19
	$	569,025	$	(9,112)	$	1	$	559,914
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	$	394,811	$	390,492
Due after one year through five years		171,049		166,257
Due after five years through ten years		—		—
Due after ten years		3,165		3,165
Total marketable securities	$	569,025	$	559,914