Fair Value Measurements - Schedule of Cash and Available-for-sale Debt Securities' Amortized Cost, Unrealized Gains (Losses) and Fair Value by Significant Investment Category (Details) - USD ($)	Mar. 31, 2022	Dec. 31, 2021
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Amortized Cost	$ 151,976,000	$ 313,777,000
Amortized Cost	1,746,364,000	1,831,593,000
Unrealized Gain	2,000	18,000
Unrealized (Loss)	(12,670,000)	(2,587,000)
Fair Value	1,733,696,000	1,829,024,000
Cash
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Amortized Cost	102,372,000	64,542,000
Unrealized Gain	0	0
Unrealized (Loss)	0	0
Fair Value	102,372,000	64,542,000
Money market funds
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Unrealized Gain	0	0
Unrealized (Loss)	0	0
Level I \| Money market funds
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Amortized Cost	36,767,000	253,075,000
Unrealized Gain	0	0
Unrealized (Loss)	0	0
Fair Value	36,767,000	253,075,000
Level II
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Amortized Cost	1,607,225,000	1,513,976,000
Unrealized Gain	2,000	18,000
Unrealized (Loss)	(12,670,000)	(2,587,000)
Fair Value	1,594,557,000	1,511,407,000
Level II \| Corporate bonds
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Amortized Cost	214,056,000	202,774,000
Unrealized Gain	2,000	16,000
Unrealized (Loss)	(1,661,000)	(289,000)
Fair Value	212,397,000	202,501,000
Level II \| U.S. treasury securities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Amortized Cost	1,041,647,000	960,278,000
Unrealized Gain	0	2,000
Unrealized (Loss)	(11,009,000)	(2,298,000)
Fair Value	1,030,638,000	957,982,000
Level II \| Commercial paper
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Amortized Cost	351,522,000	350,924,000
Unrealized Gain	0	0
Unrealized (Loss)	0	0
Fair Value	351,522,000	350,924,000
Cash & Cash Equivalents \| Fair Value, Recurring
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total assets measured at fair value on a recurring basis	151,976,000	313,777,000
Cash & Cash Equivalents \| Fair Value, Recurring \| Cash
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value	99,885,000	64,021,000
Cash & Cash Equivalents \| Fair Value, Recurring \| Level I \| Money market funds
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value	30,798,000	246,415,000
Cash & Cash Equivalents \| Fair Value, Recurring \| Level II
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value	21,293,000	3,341,000
Cash & Cash Equivalents \| Fair Value, Recurring \| Level II \| Corporate bonds
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value	0	3,341,000
Cash & Cash Equivalents \| Fair Value, Recurring \| Level II \| U.S. treasury securities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value	0	0
Cash & Cash Equivalents \| Fair Value, Recurring \| Level II \| Commercial paper
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value	21,293,000	0
Available-for-sale securities \| Fair Value, Recurring
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value	1,573,264,000	1,508,066,000
Available-for-sale securities \| Fair Value, Recurring \| Cash
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value	0	0
Available-for-sale securities \| Fair Value, Recurring \| Level I \| Money market funds
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value	0	0
Available-for-sale securities \| Fair Value, Recurring \| Level II
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value	1,573,264,000	1,508,066,000
Available-for-sale securities \| Fair Value, Recurring \| Level II \| Corporate bonds
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value	212,397,000	199,160,000
Available-for-sale securities \| Fair Value, Recurring \| Level II \| U.S. treasury securities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value	1,030,638,000	957,982,000
Available-for-sale securities \| Fair Value, Recurring \| Level II \| Commercial paper
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value	330,229,000	350,924,000
Restricted Cash (Current and Non-Current) \| Fair Value, Recurring
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total assets measured at fair value on a recurring basis	8,456,000	7,181,000
Restricted Cash (Current and Non-Current) \| Fair Value, Recurring \| Cash
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value	2,487,000	521,000
Restricted Cash (Current and Non-Current) \| Fair Value, Recurring \| Level I \| Money market funds
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value	5,969,000	6,660,000
Restricted Cash (Current and Non-Current) \| Fair Value, Recurring \| Level II
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value	0	0
Restricted Cash (Current and Non-Current) \| Fair Value, Recurring \| Level II \| Corporate bonds
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value	0	0
Restricted Cash (Current and Non-Current) \| Fair Value, Recurring \| Level II \| U.S. treasury securities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value	0	0
Restricted Cash (Current and Non-Current) \| Fair Value, Recurring \| Level II \| Commercial paper
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value	$ 0	$ 0

Cash And Cash Equivalents, Accumulated Gross Unrealized Gain, Before Tax

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Cash And Cash Equivalents, Accumulated Gross Unrealized Loss, Before Tax

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Cash And Cash Equivalents And Debt Securities, Available-For-Sale

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Cash And Cash Equivalents And Debt Securities, Available-For-Sale, Amortized Cost

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Fair value portion of probable future economic benefits obtained or controlled by an entity as a result of past transactions or events.

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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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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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Amount 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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Amount of currency on hand as well as demand deposits with banks or financial institutions. Includes other kinds of accounts that have the general characteristics of demand deposits. Also includes short-term, highly liquid investments that are both readily convertible to known amounts of cash and so near their maturity that they present insignificant risk of changes in value because of changes in interest rates. Excludes cash and cash equivalents within disposal group and discontinued operation.

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