Financial Instruments (Tables)

12 Months Ended

Dec. 31, 2019

Investments, Debt and Equity Securities [Abstract]

Summary of Cash and Available-for-Sale Securities by Significant Investment Category

The following tables summarize our cash and available-for-sale securities by significant investment category at December 31, 2019 and 2018 (in thousands):

	December 31, 2019
	Amortized Cost		Unrealized Gains		Unrealized Losses			Fair Value		Cash and Cash Equivalents		Current Marketable Securities		Non- Current Marketable Securities
Cash and cash equivalents	$	225,874	$	—	$	—		$	225,874	$	225,874	$	—	$	—
Available-for-sale:
Level 2:
Certificates of deposit	82,028		79		(6		)	82,101		10,002		69,197		2,902
U.S. treasury securities	117,891		260		(2		)	118,149		—		110,186		7,963
Debt securities of U.S. government agencies and corporate entities	834,187		2,708		(32		)	836,863		—		687,741		149,122
	$	1,259,980	$	3,047	$	(40	)	$	1,262,987	$	235,876	$	867,124	$	159,987
	December 31, 2018
	Amortized Cost		Unrealized Gains		Unrealized Losses			Fair Value		Cash and Cash Equivalents		Current Marketable Securities		Non- Current Marketable Securities
Cash and cash equivalents	$	658,365	$	20	$	(21	)	$	658,364	$	658,364	$	—	$	—
Available-for-sale:
Level 2:
Certificates of deposit	173,102		42		(36		)	173,108		—		157,920		15,188
U.S. treasury securities	152,205		18		(48		)	152,175		—		152,175		—
Debt securities of U.S. government agencies and corporate entities	712,065		40		(1,335		)	710,770		—		552,968		157,802
	$	1,695,737	$	120	$	(1,440	)	$	1,694,417	$	658,364	$	863,063	$	172,990

Amortized Cost and Estimated Fair Value of Marketable Securities, by Contractual Maturity

The amortized cost and estimated fair value of marketable securities, by contractual maturity at December 31, 2019 and 2018 are as follows (in thousands):

	December 31, 2019
	Amortized Cost		Estimated Fair Value
Due in one year or less	$	864,958	$	867,124
Due after one year through five years	159,148		159,987
Total	$	1,024,106	$	1,027,111
	December 31, 2018
	Amortized Cost		Estimated Fair Value
Due in one year or less	$	864,003	$	863,063
Due after one year through five years	173,369		172,990
Total	$	1,037,372	$	1,036,053