Available-for-Sale Securities

9 Months Ended

Sep. 30, 2017

4. Available-for-Sale Securities

As of September 30, 2017, available-for-sale securities consisted of the following (in thousands):


			Gross		Gross		Aggregate
	Amortized		Unrealized		Unrealized		Fair
	Cost		Gains		Losses		Value
U.S. treasury securities	$	16,498	$	1	$	—	$	16,499

As of December 31, 2016, available-for-sale securities consisted of the following (in thousands):


			Gross		Gross		Aggregate
	Amortized		Unrealized		Unrealized		Fair
	Cost		Gains		Losses		Value
U.S. treasury securities	$	50,004	$	—	$	(7)	$	49,997

As of September 30, 2017, there were no available-for-sale securities that have been in a continuous unrealized loss position for less than 12 months.

As of September 30, 2017, the amortized cost and fair value of available-for-sale securities by contractual maturity were (in thousands):


	Amortized		Fair
	Cost		Value
Due in one year or less	$	16,498	$	16,499
Due in one year to two years		—		—
Total	$	16,498	$	16,499