Marketable Securities (Tables)

12 Months Ended

Dec. 31, 2018

Investments, Debt and Equity Securities [Abstract]

Summary of marketable securities

The following is a summary of our marketable securities as of December 31, 2018 and 2017 (in thousands):

	December 31, 2018
			Gross		Gross			Estimated
	Amortized		Unrealized		Unrealized			Fair
Description of Securities:	Cost		Gains		Losses			Value
Short-term investments:*
Corporate debt securities	$	51,184	$	—	$	(236	)	$	50,948
U.S. treasury and government agency securities	7,647		—		(34		)	7,613
Commercial paper	3,995		—		—			3,995
Certificates of deposit	12,000		—		—			12,000
Total short-term investments	74,826		—		(270		)	74,556
Long-term investments:**
Corporate debt securities	62,530		52		(433		)	62,149
U.S. treasury and government agency securities	2,742		—		(32		)	2,710
Certificates of deposit	1,500		—		—			1,500
Total long-term investments	66,772		52		(465		)	66,359
Total investments	$	141,598	$	52	$	(735	)	$	140,915

	December 31, 2017
			Gross		Gross			Estimated
	Amortized		Unrealized		Unrealized			Fair
Description of Securities:	Cost		Gains		Losses			Value
Short-term investments:*
Corporate debt securities	$	57,257	$	—	$	(68	)	$	57,189
U.S. treasury and government agency securities	1,999		—		(13		)	1,986
Commercial paper	1,999		—		—			1,999
Certificates of deposit	9,151		—		—			9,151
Total short-term investments	70,406		—		(81		)	70,325
Long-term investments:**
Corporate debt securities	59,282		1		(320		)	58,963
U.S. treasury and government agency securities	7,381		—		(76		)	7,305
Total long-term investments	66,663		1		(396		)	66,268
Total investments	$	137,069	$	1	$	(477	)	$	136,593

* Represents marketable securities with a remaining maturity of less than one year.

** Represents marketable securities with a remaining maturity of one to three years classified as short-term on our consolidated balance sheets.