Marketable Securities

9 Months Ended

Sep. 30, 2020

4. Marketable Securities

The following table summarizes the available-for-sale debt securities held at September 30, 2020 and December 31, 2019 and (in thousands):

Description	Amortized Cost		Unrealized Gains		Unrealized Losses			Fair Value
September 30, 2020
U.S. treasury securities	$	346,066	$	—	$	(84	)	$	345,982
Corporate securities		80,814		—		(86	)		80,728
Total	$	426,880	$	—	$	(170	)	$	426,710

Description	Amortized Cost		Unrealized Gains		Unrealized Losses		Fair Value
December 31, 2019
U.S. treasury securities	$	15,936	$	6	$	—	$	15,942
Total	$	15,936	$	6	$	—	$	15,942

As of September 30, 2020, the Company held 60 securities that had been in an unrealized loss position for less than 12 months with an aggregate fair value of $377.4 million. As of December 31, 2019, the Company did not hold any securities that were in an unrealized loss position.

As of September 30, 2020, the Company had 42 securities with a fair value of $253.0 million with a contractual maturity of less than 12 months and 26 securities with a fair value of $187.5 million with a contractual maturity of greater than 12 months. As of December 31, 2019, all of the Company’s marketable securities had remaining contractual maturity dates of less than one year from the condensed consolidated balance sheet date. There were no sales of marketable securities during the nine months ended September 30, 2020 and year ending December 31, 2019.

The Company evaluates securities for other-than-temporary impairments based on quantitative and qualitative factors, and considered the decline in market value for the 60 securities in an unrealized loss position as of September 30, 2020, to be primarily attributable to the then current economic and market conditions. The Company neither intends to sell these investments nor concludes that it is more-likely-than-not that the Company will have to sell them before recovery of their carrying values. The Company also believe that it will be able to collect both principal and interest amounts due to it at maturity.