Fair Value Measurements (Tables)

12 Months Ended

Dec. 31, 2020

The following is a summary of available-for-sale marketable securities held as of December 31, 2020 and 2019 (in thousands):


			Gross Unrealized				Aggregate Fair Value		Classification on Balance Sheet
	Amortized Cost								Short-Term Marketable Securities		Long-Term Marketable Securities
As of December 31, 2020			Gains		Losses

Commercial paper	$	46,931	$	13	$	(8)	$	46,936	$	46,936	$	—
Corporate bonds	1,628,462		9,482		(262)		1,637,682		607,403		1,030,279
Municipal securities	3,495		—		(6)		3,489		—		3,489
U.S. government agency obligations	435,653		329		(63)		435,919		89,951		345,968
	$	2,114,541	$	9,824	$	(339)	$	2,124,026	$	744,290	$	1,379,736

As of December 31, 2019
Certificates of deposit	$	150,000	$	—	$	—	$	150,000	$	150,000	$	—
Commercial paper	73,829		23		(7)		73,845		73,845		—
Corporate bonds	1,368,668		1,840		(378)		1,370,130		753,538		616,592

U.S. government agency obligations	369,475		80		(74)		369,481		165,623		203,858
	$	1,961,972	$	1,943	$	(459)	$	1,963,456	$	1,143,006	$	820,450

Fair Value Measurement Within Fair Value Hierarchy

The following table details the fair value measurements within the fair value hierarchy of the Company’s financial assets and liabilities as of December 31, 2020 and 2019 (in thousands):


	Total Fair Value		Fair Value Measurements at Reporting Date Using
			Level 1		Level 2		Level 3
As of December 31, 2020
Cash Equivalents and Marketable Securities:
Money market funds	$	74,417	$	74,417	$	—	$	—

Commercial paper	75,785		—		75,785		—
Corporate bonds	1,637,682		—		1,637,682		—
Municipal securities	3,489		—		3,489		—
U.S. government agency obligations	435,919		—		435,919		—
Mutual funds	19,932		19,932		—		—
	$	2,247,224	$	94,349	$	2,152,875	$	—

As of December 31, 2019
Cash Equivalents and Marketable Securities:
Money market funds	$	50,779	$	50,779	$	—	$	—
Certificates of deposit	150,000		—		150,000		—
Commercial paper	73,845		—		73,845		—
Corporate bonds	1,370,130		—		1,370,130		—

U.S. government agency obligations	369,481		—		369,481		—
Mutual funds	15,177		15,177		—		—
	$	2,029,412	$	65,956	$	1,963,456	$	—

Schedule of Contractual Maturities of Marketable Securities and Other Investment Related Assets

Contractual maturities of the Company’s available-for-sale marketable securities held as of December 31, 2020 and 2019 were as follows (in thousands):


	December 31, 2020		December 31, 2019
Due in 1 year or less	$	744,290	$	1,143,006
Due after 1 year through 5 years	1,379,736		820,450
	$	2,124,026	$	1,963,456

Schedule of Activity of Major Classes of Assets Measured at Fair Value Using Level 3 Inputs

The following table reflects the activity for the Company’s major classes of liabilities measured at fair value using Level 3 inputs for the years ended December 31, 2020 and 2019 (in thousands):


	2020		2019
Liability:
Beginning balance	$	—	$	(6,300)

Cash paid upon achievement of milestone	—		6,300
Ending balance	$	—	$	—