Marketable Securities (Tables)

9 Months Ended

Sep. 30, 2021

Investments, Debt and Equity Securities [Abstract]

Summary of Available for Sale Securities

The amortized cost, gross unrealized holding gains or losses, and fair value of the Company’s marketable securities by major security type at each balance sheet date are summarized in the tables below (in thousands):


	September 30, 2021
	Amortized Cost		Unrealized Holding Gains		Unrealized Holding Losses		Aggregate Fair Value
Short-term marketable securities:
U.S. government treasuries(1)	$	472,214	$	13	$	(13)	$	472,214
U.S. government agency securities	15,003		—		—		15,003
Corporate debt securities(2)	61,187		5		(10)		61,182
Commercial paper	96,223		—		—		96,223
Total short-term marketable securities	644,627		18		(23)		644,622
Long-term marketable securities:
U.S. government treasuries(3)	299,225		17		(173)		299,069

Corporate debt securities(4)	20,413		2		(12)		20,403
Total long-term marketable securities	319,638		19		(185)		319,472
Total	$	964,265	$	37	$	(208)	$	964,094

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(1)Unrealized holding losses on 7 securities with an aggregate fair value of $271.8 million.

(2)Unrealized holding losses on 8 securities with an aggregate fair value of $27.8 million.

(3)Unrealized holding losses on 11 securities with an aggregate fair value of $251.5 million.

(4)Unrealized holding losses on 5 securities with an aggregate fair value of $16.8 million.


	December 31, 2020
	Amortized Cost		Unrealized Holding Gains		Unrealized Holding Losses		Aggregate Fair Value
Short-term marketable securities:
U.S. government treasuries(1)	$	878,906	$	44	$	(12)	$	878,938
U.S. government agency securities(2)	25,214		5		(2)		25,217
Corporate debt securities	27,101		79		—		27,180
Commercial paper	31,218		—		—		31,218
Total short-term marketable securities	962,439		128		(14)		962,553
Long-term marketable securities:
U.S. government treasuries	2,561		—		—		2,561

Corporate debt securities(3)	30,147		2		(11)		30,138
Total long-term marketable securities	32,708		2		(11)		32,699
Total	$	995,147	$	130	$	(25)	$	995,252

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(1)Unrealized holding losses on 19 securities with an aggregate fair value of $369.9 million.

(2)Unrealized holding losses on 2 securities with an aggregate fair value of $10.1 million.

(3)Unrealized holding losses on 1 security with an aggregate fair value of $20.1 million.