Investments (Tables)

6 Months Ended

Jun. 30, 2017

Investments, Debt and Equity Securities [Abstract]

Summary of investments

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

	June 30, 2017
			Gross		Gross			Estimated
	Amortized		Unrealized		Unrealized			Fair
	Cost		Gains		Losses			Value
Corporate debt securities
Due in one year or less	47,117		$	14	$	(25	)	$	47,106
Due in one to three years	45,992		52		(48		)	45,996
U.S. treasury and government agency securities
Due in one year or less	1,501		—		—			1,501
Due in one to three years	9,375		3		(46		)	9,332
Commercial paper
Due in one year or less	16,708		—		—			16,708
Certificates of deposit
Due in one year or less	17,000		—		—			17,000
Due in one to three years	1,452		—		—			1,452
Total investments	$	139,145	$	69	$	(119	)	$	139,095

	December 31, 2016
			Gross		Gross			Estimated
	Amortized		Unrealized		Unrealized			Fair
	Cost		Gains		Losses			Value
Corporate debt securities
Due in one year or less	$	106,430	$	3	$	(69	)	$	106,364
Due in one to three years	139,742		32		(281		)	139,493
U.S. treasury and government agency securities
Due in one year or less	1,021		—		—			1,021
Due in one to three years	11,395		—		(52		)	11,343
Commercial paper
Due in one year or less	40,560		—		—			40,560
Certificates of deposit
Due in one year or less	6,000		—		—			6,000
Total investments	$	305,148	$	35	$	(402	)	$	304,781