4. Short-Term Investments

The following table summarizes the short-term investments held at September 30, 2019 and December 31, 2018 (in thousands):


			Gross Unrealized		Gross Unrealized
	Amortized Cost		Gains		Losses		Fair Value
September 30, 2019
Corporate debt securities	$	1,850	$	—	$	—	$	1,850
Reverse repurchase agreements		21,000		—		—		21,000
Total	$	22,850	$	—	$	—	$	22,850


			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 September 30, 2019 and December 31, 2018 were one year or less. 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 investments was approximately $7.3 million. There were no short-term investments in an unrealized loss position at September 30, 2019. The Company did not hold any investments with other-than-temporary impairments at September 30, 2019 and December 31, 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 condensed consolidated results of operations. The cost of investments sold or the amount reclassified out of the accumulated other comprehensive income into other income, net is based on the specific identification method for purposes of recording realized gains and losses. All proceeds in the three and nine-month periods ended September 30, 2019 and 2018 related to maturities of underlying investments. The gains on proceeds from maturities of short-term investments were not material to the Company’s condensed consolidated results of operations for the three or nine months ended September 30, 2019 and 2018.