Investments - Summary (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Debt Securities, Available-for-sale [Line Items]
Amortized cost	$ 911,719	$ 504,305
Gross unrealized gains	130	265
Gross unrealized losses	(55)	(26)
Estimated fair value	911,794	504,544
Corporate debt securities
Debt Securities, Available-for-sale [Line Items]
Amortized cost	215,349	130,814
Gross unrealized gains	18	160
Gross unrealized losses	(41)	(4)
Estimated fair value	$ 215,326	$ 130,970
Corporate debt securities \| Maximum
Debt Securities, Available-for-sale [Line Items]
Maturity	2 years	2 years
Commercial paper
Debt Securities, Available-for-sale [Line Items]
Amortized cost	$ 528,373	$ 240,725
Gross unrealized gains	81	58
Gross unrealized losses	(1)	(18)
Estimated fair value	$ 528,453	$ 240,765
Commercial paper \| Maximum
Debt Securities, Available-for-sale [Line Items]
Maturity	1 year	1 year
U.S. Agency bonds
Debt Securities, Available-for-sale [Line Items]
Amortized cost	$ 75,244	$ 83,227
Gross unrealized gains	9	37
Gross unrealized losses	(1)	(1)
Estimated fair value	$ 75,252	$ 83,263
U.S. Agency bonds \| Maximum
Debt Securities, Available-for-sale [Line Items]
Maturity	1 year	2 years
U.S. Treasury bills
Debt Securities, Available-for-sale [Line Items]
Amortized cost	$ 83,723	$ 49,539
Gross unrealized gains	22	10
Gross unrealized losses	(10)	(3)
Estimated fair value	$ 83,735	$ 49,546
U.S. Treasury bills \| Maximum
Debt Securities, Available-for-sale [Line Items]
Maturity	2 years	2 years
Sovereign debt securities
Debt Securities, Available-for-sale [Line Items]
Amortized cost	$ 9,030
Gross unrealized gains	0
Gross unrealized losses	(2)
Estimated fair value	$ 9,028
Sovereign debt securities \| Maximum
Debt Securities, Available-for-sale [Line Items]
Maturity	1 year

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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Amount, before tax, of unrealized loss 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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Amortized cost of 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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Period between issuance and maturity of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents reported fact of one year, five months, and thirteen days.

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