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Cash and Investments in Marketable Securities - Portfolio of Cash and Investments in Marketable Securities (Detail) - USD ($) $ in Thousands | Mar. 31, 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 | $ 7,559 | 6,285
Total cash and investments in marketable securities | 1,133,409 | 1,198,558
Level 2 |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Amortized Cost | 993,849 |
Gross Unrealized Gains | 352 |
Gross Unrealized Losses | (212) |
Available-for-sale investments | 993,989 | 1,003,348
Corporate notes and bonds | Level 2 |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Amortized Cost | 510,521 |
Gross Unrealized Gains | 313 |
Gross Unrealized Losses | (171) |
Available-for-sale investments | 510,663 | 687,469
Corporate commercial paper | Level 2 |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Amortized Cost | 478,448 |
Gross Unrealized Gains | 35 |
Gross Unrealized Losses | (41) |
Available-for-sale investments | 478,442 | 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 | 4,880 |
Gross Unrealized Gains | 4 |
Gross Unrealized Losses | 0 |
Available-for-sale investments | 4,884 | 2,382
Money market funds | Level 1 |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Investments in marketable securities | 123,607 | 179,302
Certificates of Deposit |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Investments in marketable securities | $ 8,254 | $ 9,623

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