Short-Term Investments (Tables)

3 Months Ended

Dec. 30, 2017

Cash, Cash Equivalents, and Short-term Investments [Abstract]

Schedule of cash, cash equivalents and short-term investments

Cash, cash equivalents and short-term investments consist of the following (in thousands):

	December 30, 2017
	Cost Basis		Unrealized Gains		Unrealized Losses			Fair Value
Cash and cash equivalents	$	385,710	$	25	$	—		$	385,735
Short-term investments:
Available-for-sale securities:
Commercial paper	$	9,957	$	—	$	—		$	9,957
U.S. Treasury and agency obligations	18,588		19		(2		)	18,605
Corporate notes and obligations	9,127		25		(3		)	9,149
Total short-term investments	$	37,672	$	44	$	(5	)	$	37,711

	September 30, 2017
	Cost Basis		Unrealized Gains		Unrealized Losses			Fair Value
Cash and cash equivalents	$	443,066	$	—	$	—		$	443,066
Short-term investments:
Available-for-sale securities:
U.S. Treasury and agency obligations	$	21,074	$	13	$	—		$	21,087
Corporate notes and obligations	11,390		34		(1		)	11,423
Total short-term investments	$	32,464	$	47	$	(1	)	$	32,510

Schedule of amortized cost and estimated fair value of available-for-sale investments in debt securities

The amortized cost and estimated fair value of available-for-sale investments in debt securities as of December 30, 2017 and September 30, 2017 classified as short-term investments on our condensed consolidated balance sheet were as follows (in thousands):

	December 30, 2017				September 30, 2017
	Amortized Cost		Estimated Fair Value		Amortized Cost		Estimated Fair Value
Investments in available-for-sale debt securities due in less than one year	$	37,672	$	37,711	$	30,214	$	30,251
Investments in available-for-sale debt securities due in one to five years (1)	$	—	$	—	$	2,250	$	2,259

(1) Classified as short-term investments because these securities are highly liquid and can be sold at any time.