Fair Value Measurements and Fair Value of Financial Instruments - Summary of Cash Equivalents and Short-term Investments (Detail) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost Basis	$ 100,117	$ 50,145
Unrealized Gains	28	6
Unrealized Loses	(7)	(21)
Estimated Fair Value	100,138	50,130
Less: Cash Equivalents, Amortized Cost Basis	(51,391)	(152,577)
Less: Cash Equivalents, Unrealized Gains	0	0
Less: Cash Equivalents, Unrealized Loses	3	0
Less: Cash Equivalents, Estimated Fair Value	(51,388)	(152,577)
Money Market Funds [Member] \| Quoted Prices in Active Markets (Level 1) [Member]
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost Basis	15,056	126
Estimated Fair Value	15,056	126
U.S. Government Agency Securities [Member] \| Significant Other Observable Inputs (Level 2) [Member]
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost Basis	37,974	25,792
Unrealized Gains	14	1
Unrealized Loses	(2)	(4)
Estimated Fair Value	37,986	25,789
Commercial Paper [Member] \| Significant Other Observable Inputs (Level 2) [Member]
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost Basis	87,983	147,606
Unrealized Gains	8
Unrealized Loses	(8)
Estimated Fair Value	87,983	147,606
Certificates of Deposit [Member] \| Significant Other Observable Inputs (Level 2) [Member]
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost Basis		1,420
Estimated Fair Value		1,420
Corporate Bonds [Member] \| Significant Other Observable Inputs (Level 2) [Member]
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost Basis	10,495	27,778
Unrealized Gains	6	5
Unrealized Loses		(17)
Estimated Fair Value	10,501	27,766
Total Cash Equivalents and Short-term Investments [Member]
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost Basis	151,508	202,722
Unrealized Gains	28	6
Unrealized Loses	(10)	(21)
Estimated Fair Value	$ 151,526	$ 202,707

Cash and cash equivalent amortized cost.

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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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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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