Marketable Securities

6 Months Ended

Jun. 30, 2016

Investments Debt And Equity Securities [Abstract]

Marketable securities

3. Marketable securities

The following table summarizes the available-for-sale securities held at June 30, 2016 and December 31, 2015 (in thousands):

Description	Amortized Cost		Unrealized Gains		Unrealized Losses			Fair Value
June 30, 2016
U.S. government agency securities and treasuries	$	549,892	$	306	$	(81	)	$	550,117
Certificates of deposit		6,240		16		—			6,256
Total	$	556,132	$	322	$	(81	)	$	556,373
December 31, 2015
U.S. government agency securities and treasuries	$	689,425	$	22	$	(2,300	)	$	687,147
Certificates of deposit		14,360		—		(13	)		14,347
Total	$	703,785	$	22	$	(2,313	)	$	701,494

No available-for-sale securities held as of June 30, 2016 or December 31, 2015 had remaining maturities greater than three years.