Fair Value Measurements - Summary of Financial Assets Measured at Fair Value on Recurring Basis (Detail) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Financial assets
Available-for-sale marketable securities	$ 56,094	$ 199,860
Recurring [Member]
Financial assets
Total financial assets	131,783	218,573
U.S. Government Agency Obligations [Member]
Financial assets
Available-for-sale marketable securities	3,507	25,816
U.S. Government Agency Obligations [Member] \| Recurring [Member]
Financial assets
Available-for-sale marketable securities	3,507	25,816
Corporate Bonds [Member]
Financial assets
Available-for-sale marketable securities	42,083	115,890
Corporate Bonds [Member] \| Recurring [Member]
Financial assets
Available-for-sale marketable securities	42,083	115,890
Municipal Bonds [Member]
Financial assets
Available-for-sale marketable securities		3,500
Municipal Bonds [Member] \| Recurring [Member]
Financial assets
Available-for-sale marketable securities		3,500
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] \| Recurring [Member]
Financial assets
Total financial assets	75,689	18,713
Significant Other Observable Inputs (Level 2) [Member] \| Recurring [Member]
Financial assets
Total financial assets	56,094	199,860
Significant Other Observable Inputs (Level 2) [Member] \| U.S. Government Agency Obligations [Member] \| Recurring [Member]
Financial assets
Available-for-sale marketable securities	3,507	25,816
Significant Other Observable Inputs (Level 2) [Member] \| Corporate Bonds [Member] \| Recurring [Member]
Financial assets
Available-for-sale marketable securities	42,083	115,890
Significant Other Observable Inputs (Level 2) [Member] \| Municipal Bonds [Member] \| Recurring [Member]
Financial assets
Available-for-sale marketable securities		3,500
Money Market Funds [Member] \| Recurring [Member]
Financial assets
Cash and cash equivalents	75,281	18,305
Restricted cash	408	408
Money Market Funds [Member] \| Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] \| Recurring [Member]
Financial assets
Cash and cash equivalents	75,281	18,305
Restricted cash	408	408
U.S. Treasury Securities [Member] \| Recurring [Member]
Financial assets
Available-for-sale marketable securities	9,179	16,081
U.S. Treasury Securities [Member] \| Significant Other Observable Inputs (Level 2) [Member] \| Recurring [Member]
Financial assets
Available-for-sale marketable securities	9,179	16,081
Commercial Paper [Member] \| Recurring [Member]
Financial assets
Available-for-sale marketable securities	1,325	38,573
Commercial Paper [Member] \| Significant Other Observable Inputs (Level 2) [Member] \| Recurring [Member]
Financial assets
Available-for-sale marketable securities	$ 1,325	$ 38,573

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 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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Amount of cash and cash equivalents restricted as to withdrawal or usage, classified as noncurrent. Cash includes, but is not limited to, currency on hand, demand deposits with banks or financial institutions, and other accounts with general characteristics of demand deposits. Cash equivalents include, but are not limited to, 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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