Fair Value of Financial Assets - Marketable Securities (Details) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
Fair Value of Financial Assets and Liabilities
Amortized Cost	$ 317,538	$ 71,895
Gross Unrealized Gains	1	43
Gross Unrealized Losses	(60)
Fair Value	317,479	71,938
Corporate Debt Securities and Commercial Paper
Fair Value of Financial Assets and Liabilities
Amortized Cost	317,538	71,895
Gross Unrealized Gains	1	43
Gross Unrealized Losses	(60)
Fair Value	317,479	71,938
Recurring \| Estimated fair value \| Corporate Debt Securities and Commercial Paper
Fair Value of Financial Assets and Liabilities
Fair Value	317,479	71,938
Recurring \| Level 2 \| Estimated fair value \| Corporate Debt Securities and Commercial Paper
Fair Value of Financial Assets and Liabilities
Fair Value	$ 317,479	$ 71,938

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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