Investments (Tables)

12 Months Ended

Dec. 31, 2015

Investments

Summary of investments

The following is a summary of our investments as of December 31, 2015 and 2014 (in thousands):

	December 31, 2015
			Gross		Gross		Estimated
	Amortized		Unrealized		Unrealized		Fair
	Cost		Gains		Losses		Value
Corporate debt securities
Due in one year or less	$	27,964	$	—	$	(38)	$	27,926
Due in one to three years		173,652		3		(904)		172,751
Commercial paper
Due in one year or less		34,452		2		(5)		34,449
Municipal securities
Due in one year or less		2,500		—		—		2,500
Total investments	$	238,568	$	5	$	(947)	$	237,626

	December 31, 2014
			Gross		Gross		Estimated
	Amortized		Unrealized		Unrealized		Fair
	Cost		Gains		Losses		Value
Corporate debt securities
Due in one year or less	$	11,656	$	3	$	(4)	$	11,655
Due in one to three years		13,258		10		(33)		13,235
Total investments	$	24,914	$	13	$	(37)	$	24,890