| Summary of Marketable Debt Securities |
The following tables summarize our marketable debt securities: | | | | | | | | | | | | | | | | | | | | | | | | | As of June 30, 2024 | | (In thousands) | Amortized
Cost | | Gross Unrealized Gains | | Gross Unrealized Losses | | Fair Value | | U.S. treasury securities | $ | 920,578 | | | $ | 79 | | | $ | (1,671) | | | $ | 918,986 | | | U.S. government-sponsored enterprise securities | 384,165 | | | 63 | | | (727) | | | 383,501 | | | Corporate notes | 305,491 | | | 39 | | | (527) | | | 305,003 | | | Commercial paper | 76,379 | | | — | | | — | | | 76,379 | | | | | | | | | | | Municipal securities | 5,017 | | | — | | | (3) | | | 5,014 | | | Total | $ | 1,691,630 | | | $ | 181 | | | $ | (2,928) | | | $ | 1,688,883 | |
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | As of December 31, 2023 | | | | | | (In thousands) | Amortized
Cost | | Gross Unrealized Gains | | Gross Unrealized Losses | | Fair Value | | | | | | U.S. treasury securities | $ | 892,237 | | | $ | 1,085 | | | $ | (588) | | | $ | 892,734 | | | | | | | U.S. government-sponsored enterprise securities | 440,915 | | | 1,000 | | | (574) | | | 441,341 | | | | | | | Corporate notes | 252,487 | | | 945 | | | (320) | | | 253,112 | | | | | | | Commercial paper | 58,901 | | | — | | | — | | | 58,901 | | | | | | | Certificates of deposit | 3,587 | | | — | | | — | | | 3,587 | | | | | | | | | | | | | | | | | | | Total | $ | 1,648,127 | | | $ | 3,030 | | | $ | (1,482) | | | $ | 1,649,675 | | | | | |
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| Summary of Fair Value of Marketable Debt Securities |
The fair values of our marketable debt securities by classification in the condensed consolidated balance sheets were as follows: | | | | | | | | | | | | | (In thousands) | As of June 30, 2024 | | As of December 31, 2023 | | Marketable debt securities | $ | 1,646,268 | | | $ | 1,615,516 | | | Cash and cash equivalents | 42,615 | | | 34,159 | | | Total | $ | 1,688,883 | | | $ | 1,649,675 | |
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