Investments (Tables)

3 Months Ended

Mar. 31, 2015

Investments

Summary of investments

	March 31, 2015
			Gross		Gross			Estimated
	Amortized		Unrealized		Unrealized			Fair
	Cost		Gains		Losses			Value
Corporate debt securities
Due in one year or less	$	15,167	$	13	$	—		$	15,180
Due in one to three years	47,352		45		(10		)	47,387
Commercial paper
Due in one year or less	30,460		2		(1		)	30,461
Due in one to three years	—		—		—			—
Certificates of deposit
Due in one year or less	15,000		—		(1		)	14,999
Due in one to three years	—		—		—			—
Municipal securities
Due in one year or less	—		—		—			—
Due in one to three years	9,315		—		(4		)	9,311
Total investments	$	117,294	$	60	$	(16	)	$	117,338

	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