Cash and Investments in Marketable Securities

12 Months Ended

Dec. 31, 2021

Cash and Cash Equivalents [Abstract]

Cash, Cash Equivalents, and Marketable Securities

Cash and Investments in Marketable Securities

    Cash and investments in marketable securities, including cash equivalents, are as follows (in thousands):

	Estimated Fair Value at
	December 31, 2021		December 31, 2020
Cash and cash equivalents	$	25,218	$	198,955
Short-term investments	708,737		862,941
Long-term investments	64,828		136,662
Total cash and investments in marketable securities	$	798,783	$	1,198,558

    We invest in liquid, high quality debt securities. Our investments in debt securities are subject to interest rate risk. To minimize the exposure due to an adverse shift in interest rates, we invest in securities with maturities of two years or less and maintain a weighted average maturity of one year or less. All of our long-term investments as of December 31, 2021 and 2020 had maturities between one and two years.

    During the year ended December 31, 2021 and 2020, we sold available-for-sale securities totaling $11.5 million and $41.7 millions, respectively. We did not sell any available-for-sale securities in the year ended December 31, 2019. Gross realized gains and losses on those sales were not significant.

We report our accrued interest receivable, which totaled $1.4 million and $5.1 million at December 31, 2021 and December 31, 2020, respectively, in other current assets on our Consolidated Balance Sheets.

    Our portfolio of cash and investments in marketable securities includes (in thousands):

	Fair Value Hierarchy Level	December 31, 2021								December 31, 2020
		Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses		Fair Value		Fair Value
Corporate notes and bonds	2	$	278,475	$	7	$	(361)	$	278,121	$	687,469
Corporate commercial paper	2	478,932		5		(308)		478,629		313,497
Obligations of U.S. government agencies	2	5,880		—		(5)		5,875		2,382
Available-for-sale investments		763,287		12		(674)		762,625		1,003,348
Money market funds	1							23,968		179,302
Certificates of deposit	2							10,940		9,623
Cash	N/A							1,250		6,285
Total cash and investments in marketable securities								$	798,783	$	1,198,558

    At December 31, 2020, our gross unrealized gains and losses totaled $1.1 million and $0.2 million, respectively.

At both December 31, 2021 and 2020, we had letter of credit arrangements in favor of our landlords and certain vendors totaling $8.1 million. These letters of credit are secured by investments of similar amounts.