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Assets and Liabilities Measured at Fair Value (Detail) - USD ($) $ in Thousands | Dec. 31, 2020 | Dec. 31, 2019
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Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |
Assets, fair value |  | $ 81,897 |  | $ 76,865 |
Money Market Funds |  |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |
Assets, fair value | [1] | 30,360 |  | 15,369 |
U.S. Government Agency Securities |  |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |
Assets, fair value |  | 37,837 | [2] | 51,490 | [3]
Federal Agency Securities | Short-Term Investments |  |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |
Assets, fair value |  | 13,700 | [2] | 10,006 | [3]
Fair Value, Inputs, Level 1 |  |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |
Assets, fair value |  | 68,197 |  | 66,859 |
Fair Value, Inputs, Level 1 | Money Market Funds |  |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |
Assets, fair value | [1] | 30,360 |  | 15,369 |
Fair Value, Inputs, Level 1 | U.S. Government Agency Securities |  |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |
Assets, fair value |  | 37,837 | [2] | 51,490 | [3]
Fair Value, Inputs, Level 2 |  |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |
Assets, fair value |  | 13,700 |  | 10,006 |
Fair Value, Inputs, Level 2 | Federal Agency Securities | Short-Term Investments |  |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |
Assets, fair value |  | $ 13,700 | [2] | $ 10,006 | [3]
[1] | Included in cash and cash equivalents on accompanying consolidated balance sheet.
[2] | Included in short-term investments on accompanying consolidated balance sheet and are classified as available-for-sale debt securities. $2.5 million of U.S. government agency securities are included in long-term investments on the accompanying consolidated balance sheets due to the maturity being more than 12 months.
[3] | Included in short-term investments on accompanying consolidated balance sheet and are classified as available-for-sale debt securities.

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- Definition Fair value portion of probable future economic benefits obtained or controlled by an entity as a result of past transactions or events. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 820 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=117815213&loc=d3e19207-110258 + Details
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