Investments (Tables)

9 Months Ended

Sep. 30, 2017

Investments, Debt and Equity Securities [Abstract]

Summary of investments

The following is a summary of our investments as of September 30, 2017 and December 31, 2016 (in thousands):

	September 30, 2017
			Gross		Gross			Estimated
	Amortized		Unrealized		Unrealized			Fair
	Cost		Gains		Losses			Value
Short-term investments:*
Corporate debt securities	$	47,494	$	21	$	(12	)	$	47,503
Commercial paper	3,990		—		—			3,990
Certificates of deposit	11,449		—		—			11,449
Total short-term investments	62,933		21		(12		)	62,942
Long-term investments:**
Corporate debt securities	63,918		45		(52		)	63,911
U.S. treasury and government agency securities	9,378		—		(45		)	9,333
Total long-term investments	73,296		45		(97		)	73,244
Total investments	$	136,229	$	66	$	(109	)	$	136,186

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

** Represents securities with a remaining maturity of one to three years.

	December 31, 2016
			Gross		Gross			Estimated
	Amortized		Unrealized		Unrealized			Fair
	Cost		Gains		Losses			Value
Short-term investments:*
Corporate debt securities	$	106,430	$	3	$	(69	)	$	106,364
U.S. treasury and government agency securities	1,021		—		—			1,021
Commercial paper	40,560		—		—			40,560
Certificates of deposit	6,000		—		—			6,000
Total short-term investments	154,011		3		(69		)	153,945
Long-term investments:**
Corporate debt securities	139,742		32		(281		)	139,493
U.S. treasury and government agency securities	11,395		—		(52		)	11,343
Total long-term investments	151,137		32		(333		)	150,836
Total investments	$	305,148	$	35	$	(402	)	$	304,781

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

** Represents securities with a remaining maturity of one to three years.