Marketable Securities (Tables)

6 Months Ended

Mar. 31, 2018

Investments Debt And Equity Securities [Abstract]

Fair Value of Available-for-Sale Marketable Securities by Type of Security

As of March 31, 2018 and September 30, 2017, the fair value of available-for-sale marketable securities, by type of security, was as follows:

	March 31, 2018
	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Fair Value
	(in thousands)
Corporate bonds	$	162,981	$	—	$	(944	)	$	162,037
U.S. Treasury notes		32,785		—		(152	)		32,633
Commercial paper		27,313		—		—			27,313
	$	223,079	$	—	$	(1,096	)	$	221,983

	September 30, 2017
	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Fair Value
	(in thousands)
Corporate bonds	$	150,841	$	9	$	(119	)	$	150,731
U.S. Treasury notes		60,908		—		(65	)		60,843
Commercial paper		12,458		—		—			12,458
U.S. Agency bonds		4,004		—		(4	)		4,000
	$	228,211	$	9	$	(188	)	$	228,032

- Definition

Tabular disclosure of available-for-sale securities which includes, but is not limited to, changes in the cost basis and fair value, fair value and gross unrealized gain (loss), fair values by type of security, contractual maturity and classification, amortized cost basis, contracts to acquire securities to be accounted for as available-for-sale, debt maturities, transfers to trading, change in net unrealized holding gain (loss) net of tax, continuous unrealized loss position fair value, aggregate losses qualitative disclosures, other than temporary impairment (OTTI) losses or other disclosures related to available for sale securities.

+ References + Details