Marketable Securities

6 Months Ended

Jun. 30, 2019

Investments Debt And Equity Securities [Abstract]

Marketable Securities

4. Marketable Securities

As of June 30, 2019 and December 31, 2018, the fair value of available-for-sale marketable securities by type of security was as follows:

	June 30, 2019
(In thousands)	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses				Fair Value
U.S. Treasury Securities	$	3,995	$	—	$	—			$	3,995
	$	3,995	$	—	$	—			$	3,995
	December 31, 2018
(In thousands)	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses				Fair Value
U.S. Treasury Securities	$	18,424	$	—	$		(11	)	$	18,413
	$	18,424	$	—	$		(11	)	$	18,413

At June 30, 2019, marketable securities consisted of approximately $3,995,000 of investments that mature within twelve months.  At December 31, 2018, marketable securities consisted of approximately $18,413,000 of investments that mature within twelve months.