| MARKETABLE DEBT SECURITIES |
6. MARKETABLE DEBT SECURITIES We invest our excess cash balances in marketable debt securities and, at each balance sheet date presented, we classify all of our investments in debt securities as available-for-sale and as current assets as they represent the investment of funds available for current operations. We did not record any impairment charges related to our marketable debt securities during the three months ended March 31, 2025 or 2024. The following tables summarize our marketable debt securities: | | | | | | | | | | | | | | | | | | | | | | | | | As of March 31, 2025 | | (In thousands) | Amortized
Cost | | Gross Unrealized Gains | | Gross Unrealized Losses | | Fair Value | | U.S. treasury securities | $ | 802,024 | | | $ | 1,646 | | | $ | (144) | | | $ | 803,526 | | | U.S. government-sponsored enterprise securities | 416,708 | | | 567 | | | (201) | | | 417,074 | | | Corporate notes | 372,040 | | | 813 | | | (117) | | | 372,736 | | | Commercial paper | 47,926 | | | — | | | — | | | 47,926 | | | | | | | | | | | Municipal securities | 5,000 | | | 10 | | | — | | | 5,010 | | | Total | $ | 1,643,698 | | | $ | 3,036 | | | $ | (462) | | | $ | 1,646,272 | |
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | As of December 31, 2024 | | | | | | (In thousands) | Amortized
Cost | | Gross Unrealized Gains | | Gross Unrealized Losses | | Fair Value | | | | | | U.S. treasury securities | $ | 957,145 | | | $ | 1,377 | | | $ | (467) | | | $ | 958,055 | | | | | | | U.S. government-sponsored enterprise securities | 405,890 | | | 575 | | | (370) | | | 406,095 | | | | | | | Corporate notes | 361,311 | | | 769 | | | (341) | | | 361,739 | | | | | | | Commercial paper | 58,117 | | | — | | | — | | | 58,117 | | | | | | | | | | | | | | | | | | | Municipal securities | 5,002 | | | 1 | | | — | | | 5,003 | | | | | | | Total | $ | 1,787,465 | | | $ | 2,722 | | | $ | (1,178) | | | $ | 1,789,009 | | | | | |
The fair values of our marketable debt securities by classification in the condensed consolidated balance sheets were as follows: | | | | | | | | | | | | | (In thousands) | As of March 31, 2025 | | As of December 31, 2024 | | Marketable debt securities | $ | 1,605,368 | | | $ | 1,719,920 | | | Cash and cash equivalents | 40,904 | | | 69,089 | | | Total | $ | 1,646,272 | | | $ | 1,789,009 | |
|