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Investments and Fair Value Measurements - Cash, Cash Equivalent and Marketable Securities (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020	Sep. 30, 2020
Debt Securities, Available-for-sale [Line Items]
Cash and cash equivalents:	$ 282,131	$ 62,900	$ 309,968
Marketable securities, current	361,290	131,283
Marketable securities, noncurrent	429,489	20,448
Total marketable securities	790,779	151,731
Total cash, cash equivalents and marketable securities	1,072,910	214,631
Corporate notes and bonds
Debt Securities, Available-for-sale [Line Items]
Marketable securities, current	3,129	14,314
Marketable securities, noncurrent	131,177	0
Total marketable securities	134,306	14,314
Commercial paper
Debt Securities, Available-for-sale [Line Items]
Marketable securities, current	134,015	41,445
Total marketable securities	134,015	41,445
U.S. Treasury securities
Debt Securities, Available-for-sale [Line Items]
Marketable securities, current	190,183	75,524
Marketable securities, noncurrent	220,291	20,448
Total marketable securities	410,474	95,972
Foreign government and supranational securities
Debt Securities, Available-for-sale [Line Items]
Marketable securities, current	10,025	0
Marketable securities, noncurrent	20,359	0
Total marketable securities	30,384
Municipal securities
Debt Securities, Available-for-sale [Line Items]
Marketable securities, current	2,250	0
Total marketable securities	4,580
Municipal securities
Debt Securities, Available-for-sale [Line Items]
Marketable securities, noncurrent	2,330	0
Asset-backed securities
Debt Securities, Available-for-sale [Line Items]
Marketable securities, current	21,688	0
Marketable securities, noncurrent	55,332	0
Total marketable securities	77,020
Cash
Debt Securities, Available-for-sale [Line Items]
Cash and cash equivalents:	21,832	21,273
Money market funds
Debt Securities, Available-for-sale [Line Items]
Cash and cash equivalents:	259,699	36,629
Commercial paper
Debt Securities, Available-for-sale [Line Items]
Cash and cash equivalents:	0	4,998
Municipal securities
Debt Securities, Available-for-sale [Line Items]
Cash and cash equivalents:	400	0
Certificate of deposit
Debt Securities, Available-for-sale [Line Items]
Cash and cash equivalents:	$ 200	$ 0

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