Available-for-Sale Securities (Tables)

3 Months Ended

Mar. 31, 2017

Available-for-Sale Securities

Summary of Available-for-Sale Securities

As of March 31, 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	$	256,290	$	—	$	(12)	$	256,278

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

Summary of Fair Value and Gross Unrealized Losses of Available-for-Sale Securities in a Continuous Unrealized Loss Position

As of March 31, 2017, the fair value and gross unrealized losses of available-for-sale securities that have been in a continuous unrealized loss position for less than 12 months were as follows (in thousands):

	Aggregate		Gross
	Fair		Unrealized
	Value		Losses
U.S. treasury securities	$	256,278	$	(12)

Summary of Amortized Cost and Fair Value of Available-for-Sale Securities by Contractual Maturity

As of March 31, 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	$	256,290	$	256,278
Due in one year to two years		—		—
Total	$	256,290	$	256,278