Marketable Securities

12 Months Ended

Sep. 30, 2019

Investments Debt And Equity Securities [Abstract]

Marketable Securities

4. Marketable Securities

As of September 30, 2019 and 2018, the fair value of available-for-sale marketable securities, by type of security, was as follows:

	September 30, 2019
	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Fair Value
	(in thousands)
U.S. Treasury notes	$	170,519	$	60	$	(64	)	$	170,515
Corporate bonds		111,690		170		(23	)		111,837
Commercial paper		66,667		—		—			66,667
	$	348,876	$	230	$	(87	)	$	349,019

	September 30, 2018
	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Fair Value
	(in thousands)
Commercial paper	$	113,885	$	—	$	—		$	113,885
Corporate bonds		105,105		1		(477	)		104,629
U.S. Treasury notes		42,801		—		(98	)		42,703
	$	261,791	$	1	$	(575	)	$	261,217

As of September 30, 2019 and 2018, marketable securities consisted of investments that mature within one year, with the exception of certain corporate bonds and U.S. Treasury notes, which have maturities between one and three years and an aggregate fair value of $65,013 and $16,389, respectively.