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Cash and Investments in Marketable Securities - Portfolio of Cash and Investments in Marketable Securities (Detail) - USD ($) $ in Thousands | Dec. 31, 2020 | Dec. 31, 2019
--- | --- | ---
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Gross Unrealized Gains |  | $ 2,100
Gross Unrealized Losses |  | (300)
Cash | $ 6,285 | 5,829
Total cash and investments in marketable securities | 1,198,558 | 1,603,981
Fair Value Hierarchy Level 2 |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Amortized Cost | 1,002,443 |
Gross Unrealized Gains | 1,081 |
Gross Unrealized Losses | (176) |
Fair Value | 1,003,348 | 1,507,655
Corporate Notes and Bonds | Fair Value Hierarchy Level 2 |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Amortized Cost | 686,543 |
Gross Unrealized Gains | 1,035 |
Gross Unrealized Losses | (109) |
Fair Value | 687,469 | 1,132,182
Commercial Paper | Fair Value Hierarchy Level 2 |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Amortized Cost | 313,520 |
Gross Unrealized Gains | 44 |
Gross Unrealized Losses | (67) |
Fair Value | 313,497 | 375,473
Obligations of U.S. government agencies | Fair Value Hierarchy Level 2 |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Amortized Cost | 2,380 |
Gross Unrealized Gains | 2 |
Gross Unrealized Losses | 0 |
Fair Value | 2,382 | 0
Money Market Funds | Fair Value Hierarchy Level 1 |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Investments in marketable securities | 179,302 | 83,546
Certificates of Deposit |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Investments in marketable securities | $ 9,623 | $ 6,951

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