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Significant Accounting Policies - Estimated Fair Value of Assets and Liability (Detail) - Fair Value, Measurements, Recurring - USD ($) $ in Thousands | Mar. 31, 2022 | Dec. 31, 2021
--- | --- | ---
Asset: |  |
Asset, fair value | $ 314,574 | $ 374,911
Level 1 |  |
Asset: |  |
Asset, fair value | 136,250 | 118,282
Level 2 |  |
Asset: |  |
Asset, fair value | 178,324 | 256,629
Money Market Fund |  |
Asset: |  |
Asset, fair value | 129,031 | 95,063
Money Market Fund | Level 1 |  |
Asset: |  |
Asset, fair value | 129,031 | 95,063
U.S. Treasury Shares |  |
Asset: |  |
Asset, fair value | 7,219 | 23,219
U.S. Treasury Shares | Level 1 |  |
Asset: |  |
Asset, fair value | 7,219 | 23,219
Corporate Bonds |  |
Asset: |  |
Asset, fair value | 59,944 | 83,587
Corporate Bonds | Level 2 |  |
Asset: |  |
Asset, fair value | 59,944 | 83,587
Commercial Paper |  |
Asset: |  |
Asset, fair value | 73,652 | 121,773
Commercial Paper | Level 2 |  |
Asset: |  |
Asset, fair value | 73,652 | 121,773
Repo Securities |  |
Asset: |  |
Asset, fair value | 4,750 | 8,000
Repo Securities | Level 2 |  |
Asset: |  |
Asset, fair value | 4,750 | 8,000
Asset Backed Securities |  |
Asset: |  |
Asset, fair value | 6,707 | 8,816
Asset Backed Securities | Level 2 |  |
Asset: |  |
Asset, fair value | 6,707 | 8,816
Certificate of Deposit |  |
Asset: |  |
Asset, fair value | 24,603 | 21,553
Certificate of Deposit | Level 2 |  |
Asset: |  |
Asset, fair value | 24,603 | 21,553
Non-US Government |  |
Asset: |  |
Asset, fair value | 8,668 | 12,900
Non-US Government | Level 2 |  |
Asset: |  |
Asset, fair value | $ 8,668 | $ 12,900

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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=123874694&loc=d3e19207-110258 + Details
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