4. Short-Term Investments

The following table summarizes the short-term investments held at December 31, 2019 and 2018 (in thousands):


			Gross Unrealized		Gross Unrealized
	Amortized Cost		Gains		Losses		Fair Value
December 31, 2019
Commercial paper	$	1,993	$	—	$	—	$	1,993
Corporate debt securities		3,352		—		—		3,352
Reverse repurchase agreements		21,000		—		—		21,000
Total	$	26,345	$	—	$	—	$	26,345


			Gross Unrealized		Gross Unrealized
	Amortized Cost		Gains		Losses		Fair Value
December 31, 2018
Corporate debt securities	$	7,280	$	—	$	(4)	$	7,276
Reverse repurchase agreements		15,000		—		—		15,000
Total	$	22,280	$	—	$	(4)	$	22,276

The contractual maturities of all short-term investments held at December 31, 2019 and 2018 were one year or less. There were four short-term investments in an unrealized loss position at December 31, 2019, none of which had been in an unrealized loss position for more than 12 months. The aggregate fair value of these securities at December 31, 2019 was approximately $3.4 million. There were seven short-term investments in an unrealized loss position at December 31, 2018, none of which had been in an unrealized loss position for more than 12 months. The aggregate fair value of these securities at December 31, 2018 was approximately $7.3 million. The Company did not hold any securities with other-than-temporary impairments at December 31, 2019 and 2018.

Gross realized gains and losses on the sales of short-term investments are included in other income, net. Unrealized holding gains or losses for the period that have been included in accumulated other comprehensive income, as well as gains and losses reclassified out of accumulated other comprehensive income into other income, net were not material to the Company’s consolidated results of operations. During the years ended December 31, 2019 and 2018 all proceeds related to maturities of underlying securities. The gains on proceeds of maturities of short-term investments were not material to the Company’s consolidated results of operations for the years ended December 31, 2019 and 2018.