Fair Value Measurements and Fair Value of Financial Instruments - Summary of Cash Equivalents and Short-term Investments (Detail) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Debt Securities, Available-for-sale [Line Items]
Amortized Cost Basis	$ 299,762	$ 367,191
Unrealized Gains	18	121
Unrealized Losses	(46)	(7)
Estimated Fair Value	299,734	367,305
Less: Cash Equivalents, Amortized Cost Basis	(27,019)	(58,894)
Less: cash equivalents	0	0
Less: Cash equivalents, unrealized losses	0	3
Less: Cash equivalents, estimated fair value	(27,019)	(58,891)
Corporate bonds \| Level 2
Debt Securities, Available-for-sale [Line Items]
Amortized Cost Basis	51,986
Unrealized Gains	0
Unrealized Losses	(16)
Estimated Fair Value	51,970
Total cash equivalents and short-term investments
Debt Securities, Available-for-sale [Line Items]
Amortized Cost Basis	326,781	426,085
Unrealized Gains	18	121
Unrealized Losses	(46)	(10)
Estimated Fair Value	326,753	426,196
Money market funds \| Level 1
Debt Securities, Available-for-sale [Line Items]
Amortized Cost Basis	27,019	178
Unrealized Gains	0	0
Unrealized Losses	0	0
Estimated Fair Value	27,019	178
U.S. government and agency securities \| Level 2
Debt Securities, Available-for-sale [Line Items]
Amortized Cost Basis	90,665	328,583
Unrealized Gains	8	121
Unrealized Losses	(25)	(5)
Estimated Fair Value	90,648	328,699
Commercial paper \| Level 2
Debt Securities, Available-for-sale [Line Items]
Amortized Cost Basis	157,111	97,324
Unrealized Gains	10	0
Unrealized Losses	(5)	(5)
Estimated Fair Value	$ 157,116	$ 97,319

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Cash and cash equivalent gross unrealized gain.

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Cash and cash equivalent gross unrealized loss.

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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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Fair value portion 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.

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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