SHORT-TERM INVESTMENTS

We consider all highly liquid investments with maturities of three months or less at the time of purchase to be cash equivalents. Investments classified as available-for-sale are reported at fair value with unrealized gains and losses, net of related income taxes, recorded as a separate component of other comprehensive income (“OCI”) in stockholders’ equity until realized. Interest and amortization of premiums and discounts for debt securities are included in interest income. Gains and losses on securities sold are determined based on the specific identification method and are included in other income (expense).

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



	March 31, 2018
	Cost Basis		Unrealized Gains		Unrealized Losses			Fair Value
Cash and cash equivalents	$	308,987	$	—	$	—		$	308,987

Short-term investments:
Available-for-sale securities:
Commercial paper	$	14,994	$	—	$	—		$	14,994
U.S. Treasury and agency obligations	14,994		—		(1		)	14,993
Corporate notes and obligations	7,117		27		(4		)	7,140
Total short-term investments	$	37,105	$	27	$	(5	)	$	37,127



	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

None of the $5,000 in unrealized losses at March 31, 2018 were considered to be other-than-temporary impairments.

The amortized cost and estimated fair value of available-for-sale investments in debt securities as of March 31, 2018 and September 30, 2017 classified as short-term investments on our condensed consolidated balance sheet were as follows (in thousands):



	March 31, 2018				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	$	34,105	$	34,119	$	30,214	$	30,251
Investments in available-for-sale debt securities due in one to five years ⁽¹⁾	$	3,000	$	3,008	$	2,250	$	2,259

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

During the three and six months ended March 31, 2018, we received proceeds totaling $0.0 million and $2.4 million, respectively, from the sale of available-for-sale securities and realized no gross gains or losses. During the three and six months ended April 1, 2017, we received proceeds totaling $0.0 million and $0.1 million, respectively, from the sale of available-for-sale securities and realized no gross gains or losses.