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Investments and Fair Value Measurements - Available-For-Sale Investments (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	$ 790,872	$ 151,626
Gross Unrealized Gain	50	110
Gross Unrealized Loss	(143)	(5)
Fair Value	790,779	151,731
Corporate notes and bonds
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	134,282	14,297
Gross Unrealized Gain	42	17
Gross Unrealized Loss	(18)	0
Fair Value	134,306	14,314
Commercial paper
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	134,038	41,445
Gross Unrealized Gain	0	0
Gross Unrealized Loss	(23)	0
Fair Value	134,015	41,445
U.S. Treasury securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	410,542	95,884
Gross Unrealized Gain	6	93
Gross Unrealized Loss	(74)	(5)
Fair Value	410,474	$ 95,972
Municipal securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	4,578
Gross Unrealized Gain	2
Gross Unrealized Loss	0
Fair Value	4,580
Asset-backed securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	77,038
Gross Unrealized Gain	0
Gross Unrealized Loss	(18)
Fair Value	77,020
Foreign government and supranational securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	30,394
Gross Unrealized Gain	0
Gross Unrealized Loss	(10)
Fair Value	$ 30,384

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Amount, before tax, of unrealized gain in accumulated other comprehensive income (AOCI) on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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