Marketable Securities (Tables)

12 Months Ended

Dec. 31, 2017

Cash and Cash Equivalents [Abstract]

Summary of cash, cash equivalents and marketable securities

A summary of the Company’s cash, cash equivalents and marketable securities is shown below:

	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Fair Value
	(in thousands)
December 31, 2017
Cash and cash equivalents:
Cash and money market funds	$	1,595,377	$	—	$	—		$	1,595,377
Government-sponsored enterprise securities	12,679		—		(1		)	12,678
Commercial paper	57,371		—		(14		)	57,357
Total cash and cash equivalents	$	1,665,427	$	—	$	(15	)	$	1,665,412
Marketable securities:
Corporate equity securities	$	43,213	$	31,608	$	—		$	74,821
Government-sponsored enterprise securities	2,304		—		(1		)	2,303
Corporate debt securities (matures within 1 year)	215,639		—		(363		)	215,276
Corporate debt securities (matures after 1 year through 5 years)	50,697		—		(106		)	50,591
Commercial paper (matures within 1 year)	80,372		—		(109		)	80,263
Total marketable securities	392,225		31,608		(579		)	423,254
Total cash, cash equivalents and marketable securities	$	2,057,652	$	31,608	$	(594	)	$	2,088,666
December 31, 2016
Cash and cash equivalents:
Cash and money market funds	$	1,183,945	$	—	$	—		$	1,183,945
Total cash and cash equivalents	$	1,183,945	$	—	$	—		$	1,183,945
Marketable securities:
Corporate equity securities	$	43,213	$	21,347	$	—		$	64,560
Government-sponsored enterprise securities (matures within 1 year)	15,506		2		—			15,508
Corporate debt securities (matures within 1 year)	111,225		—		(85		)	111,140
Commercial paper (matures within 1 year)	59,331		73		—			59,404
Total marketable securities	229,275		21,422		(85		)	250,612
Total cash, cash equivalents and marketable securities	$	1,413,220	$	21,422	$	(85	)	$	1,434,557