4.CASH, CASH EQUIVALENTS, AND MARKETABLE SECURITIES

The amortized cost, gross unrealized gains and losses, and fair value of cash, cash equivalents, and marketable securities as of December 31, 2020 and 2019, are as follows (in thousands):


	December 31, 2020
	Cost		Unrealized		Unrealized				Cash and Cash		Marketable
	Basis		Gains		Losses		Fair Value		Equivalents		Securities
Cash	$	709,924	$	—	$	—	$	709,924	$	709,924	$	—
Money market funds		618,197		—		—		618,197		618,197		—
Commercial paper		81,037		1		—		81,038		81,038		—
Corporate debt securities		29,891		26		(2)		29,915		3,506		26,409
Asset-backed securities		12,518		19		(4)		12,533		—		12,533
U.S. agency securities		6,993		2		—		6,995		—		6,995
U.S. Treasury securities		1,700		—		—		1,700		—		1,700
Total	$	1,460,260	$	48	$	(6)	$	1,460,302	$	1,412,665	$	47,637


	December 31, 2019
	Cost		Unrealized		Unrealized				Cash and Cash		Marketable
	Basis		Gains		Losses		Fair Value		Equivalents		Securities
Cash	$	366,358	$	—	$	—	$	366,358	$	366,358	$	—
Money market funds		30,935		—		—		30,935		30,935		—
Commercial paper		19,997		1		(4)		19,994		7,038		12,956
Corporate debt securities		16,417		12		(1)		16,428		—		16,428
Asset-backed securities		12,482		12		(2)		12,492		—		12,492
U.S. agency securities		749		—		—		749		749		—
U.S. Treasury securities		1,000		—		—		1,000		—		1,000
Non-U.S. securities		700		—		—		700		—		700
Total	$	448,638	$	25	$	(7)	$	448,656	$	405,080	$	43,576

A summary of debt securities with unrealized losses aggregated by period of continuous unrealized loss is as follows (in thousands):


	Less than 12 Months				12 Months or Greater				Total
	Fair		Unrealized		Fair		Unrealized		Fair		Unrealized
December 31, 2020	Value		Losses		Value		Losses		Value		Losses
Commercial paper	$	19,296	$	—	$	—	$	—	$	19,296	$	—
Corporate-debt securities		7,538		(2)		—		—		7,538		(2)
Asset-backed securities		4,611		(4)		—		—		4,611		(4)
Total	$	31,445	$	(6)	$	—	$	—	$	31,445	$	(6)


	Less than 12 Months				12 Months or Greater				Total
	Fair		Unrealized		Fair		Unrealized		Fair		Unrealized
December 31, 2019	Value		Losses		Value		Losses		Value		Losses
Commercial paper	$	15,059	$	(4)	$	—	$	—	$	15,059	$	(4)
Corporate-debt securities		3,166		(1)		—		—		3,166		(1)
Asset-backed securities		4,258		(2)		—		—		4,258		(2)
Non-U.S. securities		700		—		—		—		700		—
Total	$	23,183	$	(7)	$	—	$	—	$	23,183	$	(7)

The scheduled contractual maturities of debt securities as of December 31, 2019 are as follows (in thousands):


					After
					1 Year
			Within		through
December 31, 2020	Fair Value		1 Year		5 Years
Commercial paper	$	81,038	$	81,038	$	—
Corporate-debt securities		29,915		29,915		—
Asset-backed securities		12,533		12,533		—
U.S. agency securities		6,995		6,995		—
U.S. Treasury securities		1,700		1,700		—
Total	$	132,181	$	132,181	$	—