Investments (Tables)

9 Months Ended

Sep. 30, 2015

Investments

Summary of investments

	September 30, 2015
			Gross		Gross		Estimated
	Amortized		Unrealized		Unrealized		Fair
	Cost		Gains		Losses		Value
Corporate debt securities
Due in one year or less	$	26,244	$	8	$	(10)	$	26,242
Due in one to three years		147,615		25		(276)		147,364
Commercial paper
Due in one year or less		7,488		2		—		7,490
Certificates of deposit
Due in one year or less		10,000		1		—		10,001
Municipal securities
Due in one year or less		13,874		11		—		13,885
Due in one to three years		70,249		117		(5)		70,361
Total investments	$	275,470	$	164	$	(291)	$	275,343

	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