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Cash and Investments in Marketable Securities - Portfolio of Cash and Investments in Marketable Securities (Detail) - USD ($) $ in Thousands | Sep. 30, 2021 | Dec. 31, 2020
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Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Gross Unrealized Gains |  | $ 1,100
Gross Unrealized Losses |  | (200)
Cash | $ 5,681 | 6,285
Total cash and investments in marketable securities | 955,299 | 1,198,558
Level 2 |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Amortized Cost | 891,245 |
Gross Unrealized Gains | 90 |
Gross Unrealized Losses | (190) |
Fair Value | 891,145 | 1,003,348
Corporate notes and bonds | Level 2 |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Amortized Cost | 329,376 |
Gross Unrealized Gains | 53 |
Gross Unrealized Losses | (90) |
Fair Value | 329,339 | 687,469
Corporate commercial paper | Level 2 |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Amortized Cost | 555,989 |
Gross Unrealized Gains | 35 |
Gross Unrealized Losses | (100) |
Fair Value | 555,924 | 313,497
Obligations of U.S. government agencies | Level 2 |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Amortized Cost | 5,880 |
Gross Unrealized Gains | 2 |
Gross Unrealized Losses | 0 |
Fair Value | 5,882 | 2,382
Money market funds | Level 1 |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Money market funds | 48,336 | 179,302
Certificates of deposit |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Money market funds | $ 10,137 | $ 9,623

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