Investments (Tables)

3 Months Ended

Mar. 31, 2016

Investments

Summary of investments

The following is a summary of our investments as of March 31, 2016 and December 31, 2015 (in thousands):

	March 31, 2016
			Gross		Gross		Estimated
	Amortized		Unrealized		Unrealized		Fair
	Cost		Gains		Losses		Value
Corporate debt securities
Due in one year or less	$	56,886	$	7	$	(43)	$	56,850
Due in one to three years		193,452		596		(89)		193,959
U.S. treasury and government agency securities
Due in one year or less		4,496		32		—		4,528
Commercial paper
Due in one year or less		18,973		4		—		18,977
Municipal securities
Due in one year or less		2,500		2		—		2,502
Total investments	$	276,307	$	641	$	(132)	$	276,816

	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