MARKETABLE SECURITIES (Tables)

3 Months Ended

Mar. 31, 2018

Investments Debt And Equity Securities [Abstract]

Summary of Company's Marketable Securities

The following tables summarize our marketable securities at March 31, 2018 and December 31, 2017, in thousands:

	At March 31, 2018
	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Fair Value
Certificates of deposit	$	33,541	$	—	$	—		$	33,541
Commercial paper		96,539		—		—			96,539
Corporate notes		401,930		5		(900	)		401,035
U.S. government-sponsored enterprise securities		379,692		—		(831	)		378,861
U.S. treasury securities		262,722		—		(335	)		262,387
Total	$	1,174,424	$	5	$	(2,066	)	$	1,172,363

	At December 31, 2017
	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Fair Value
Certificates of deposit	$	30,200	$	—	$	—		$	30,200
Commercial paper		56,951		—		—			56,951
Corporate notes		373,736		11		(495	)		373,252
U.S. government-sponsored enterprise securities		399,281		—		(983	)		398,298
U.S. treasury securities		200,649		1		(175	)		200,475
Total	$	1,060,817	$	12	$	(1,653	)	$	1,059,176

Summary of Available-For-Sale Debt Securities by Contractual Maturity

The following table summarizes our available-for-sale debt securities by contractual maturity, at March 31, 2018, in thousands:

	At March 31, 2018
	AmortizedCost		Fair Value
Less than one year	$	1,173,776	$	1,171,715
Greater than one year but less than two years		648		648
Total	$	1,174,424	$	1,172,363