MARKETABLE DEBT SECURITIES (Tables)

12 Months Ended

Dec. 31, 2020

Investments, Debt and Equity Securities [Abstract]

Summary of Company's Marketable Debt Securities

The following tables summarize our marketable debt securities:

	As of December 31, 2020
(In thousands)	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses		Fair Value
U.S. government-sponsored enterprise securities	$	245,113	$	135	$	(34)	$	245,214
U.S. treasury securities	1,107,721		328		(81)		1,107,968
Total	$	1,352,834	$	463	$	(115)	$	1,353,182

	As of December 31, 2019
(In thousands)	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses		Fair Value
Certificates of deposit	$	4,303	$	—	$	(2)	$	4,301
Commercial paper	39,913		—		—		39,913
Corporate notes	146,016		58		(34)		146,040
U.S. government-sponsored enterprise securities	32,487		3		(2)		32,488
U.S. treasury securities	1,092,293		185		(71)		1,092,407
Total	$	1,315,012	$	246	$	(109)	$	1,315,149

Summary of Fair Value of Marketable Debt Securities

The fair values of our marketable debt securities by classification in the consolidated balance sheets were as follows:

(In thousands)	December 31, 2020		December 31, 2019
Cash and cash equivalents	$	20,000	$	340,132
Marketable debt securities	1,333,182		975,017
Total	$	1,353,182	$	1,315,149