Marketable Securities

6 Months Ended

Mar. 31, 2017

Investments Debt And Equity Securities [Abstract]

Marketable Securities

4. Marketable Securities

As of March 31, 2017 and September 30, 2016, the fair value of available-for-sale marketable securities, by type of security, was as follows:

	March 31, 2017
	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Fair Value
Corporate bonds	$	112,572	$	34	$	(103	)	$	112,503
U.S. Treasury notes		82,523		8		(98	)		82,433
Commercial paper		17,756		—		—			17,756
U.S. Agency bonds		9,014		—		(14	)		9,000
	$	221,865	$	42	$	(215	)	$	221,692

	September 30, 2016
	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Fair Value
Corporate bonds	$	76,077	$	27	$	(31	)	$	76,073
U.S. Treasury notes		69,579		38		(9	)		69,608
Commercial paper		49,900		—		—			49,900
U.S. Agency bonds		30,040		15		(10	)		30,045
	$	225,596	$	80	$	(50	)	$	225,626

As of March 31, 2017, marketable securities consisted of investments that mature within one year, with the exception of certain U.S. Treasury notes and corporate bonds, which have maturities within three years and an aggregate fair value of $65,330.