Marketable Securities

3 Months Ended

Mar. 31, 2019

Investments Debt And Equity Securities [Abstract]

Marketable securities

3. Marketable securities

The following table summarizes the marketable securities held at March 31, 2019 and December 31, 2018 (in thousands):

Description	Amortized cost / Cost		Unrealized gains		Unrealized losses			Fair value
March 31, 2019
U.S. government agency securities and treasuries	$	1,357,641	$	1,604	$	(1,400	)	$	1,357,845
Certificates of deposit		5,960		—		—			5,960
Corporate bonds		83,536		81		(19	)		83,598
Commercial paper		42,542		—		—			42,542
Equity securities		20,017		—		(934	)		19,083
Total	$	1,509,696	$	1,685	$	(2,353	)	$	1,509,028
December 31, 2018
U.S. government agency securities and treasuries	$	1,459,649	$	963	$	(3,011	)	$	1,457,601
Certificates of deposit		9,080		—		—			9,080
Equity securities		20,017		2,150		—			22,167
Total	$	1,488,746	$	3,113	$	(3,011	)	$	1,488,848

No available-for-sale debt securities held as of March 31, 2019 or December 31, 2018 had remaining maturities greater than three years.