Marketable Securities (Tables)

12 Months Ended

Sep. 30, 2022

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
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
September 30, 2021:
Bank certificates of deposits	$	30	$	—	$	—	$	30
Corporate securities		3,624		—		—		3,624
Municipal securities		—		—		—		—
Other debt securities		25		—		—		25
	$	3,679	$	—	$	—	$	3,679

Fair Value of Marketable Securities by Contractual Maturity

	Amortized
	Cost			Fair Value
Due in one year or less	$	914,706	$	909,913
Due after one year through five years		360,930		351,085
Due after five years through ten years		—		—
Due after ten years		2,786		2,786
Total marketable securities	$	1,278,422	$	1,263,784