MARKETABLE SECURITIES

As of September 30, 2018 and December 31, 2017, our marketable securities were classified as available-for-sale in accordance with accounting standards which provide guidance related to accounting and classification of certain investments in marketable securities. Available-for-sale marketable securities are those securities which we view as available for use in current operations, if needed. We generally classify our available-for-sale marketable securities as short-term investments on our condensed consolidated balance sheets even though the stated maturity date may be one year or more beyond the current balance sheet date.

The following is a summary of our marketable securities as of September 30, 2018 and December 31, 2017 (in thousands):



	September 30, 2018
			Gross		Gross			Estimated
	Amortized		Unrealized		Unrealized			Fair
	Cost		Gains		Losses			Value
Short-term marketable securities:*
Corporate debt securities	$	53,862	$	1	$	(174	)	$	53,689
Certificates of deposit	13,000		—		—			13,000
U.S. treasury and government agency securities	6,149		—		(29		)	6,120
Commercial paper	5,462		—		—			5,462
Total short-term marketable securities	$	78,473	$	1	$	(203	)	$	78,271
Long-term marketable securities:**
Corporate debt securities	$	55,017	$	2	$	(580	)	$	54,439
U.S. treasury and government agency securities	6,236		—		(78		)	6,158
Certificates of deposit	1,500		—		—			1,500
Total long-term marketable securities	62,753		2		(658		)	62,097
Total marketable securities	$	141,226	$	3	$	(861	)	$	140,368

* Represents marketable securities with a remaining maturity of less than one year.

** Represents marketable securities with a remaining maturity of one to three years.



	December 31, 2017
			Gross		Gross			Estimated
	Amortized		Unrealized		Unrealized			Fair
	Cost		Gains		Losses			Value
Short-term marketable securities:*
Corporate debt securities	$	57,257	$	—	$	(68	)	$	57,189
Certificates of deposit	9,151		—		—			9,151
U.S. treasury and government agency securities	1,999		—		(13		)	1,986
Commercial paper	1,999		—		—			1,999
Total short-term marketable securities	$	70,406	$	—	$	(81	)	$	70,325
Long-term marketable securities:**
Corporate debt securities	$	59,282	$	1	$	(320	)	$	58,963
U.S. treasury and government agency securities	7,381		—		(76		)	7,305
Total long-term marketable securities	66,663		1		(396		)	66,268
Total marketable securities	$	137,069	$	1	$	(477	)	$	136,593

* Represents marketable securities with a remaining maturity of less than one year.

** Represents marketable securities with a remaining maturity of one to three years.

Impairments and Unrealized Gains and Losses on Marketable Securities

We did not recognize any other-than-temporary impairment losses in our condensed consolidated statements of operations related to our marketable securities during the three and nine months ended September 30, 2018 and 2017. We considered various factors, including the length of time that each security was in an unrealized loss position and our ability and intent to hold these securities until the recovery of their amortized cost basis occurs. As of September 30, 2018, we had no material losses in an unrealized loss position for more than one year. Future events may occur, or additional information may become available, which may cause us to identify credit losses where we do not expect to receive cash flows sufficient to recover the entire amortized cost basis of a security and may necessitate the recording of future realized losses on securities in our portfolio. Significant losses in the estimated fair values of our marketable securities could have a material adverse effect on our earnings in future periods.