Available-for-Sale Securities and Fair Value Measurements | Available-for-Sale Securities and Fair Value Measurements The available-for-sale securities in our Condensed Consolidated Balance Sheets are as follows: March 31, December 31, (in thousands) Cash equivalents $ 30,540 $ 50,524 Short-term marketable securities 320,578 364,506 Long-term marketable securities 81,834 36,196 Total marketable securities $ 432,952 $ 451,226 The following table presents our available-for-sale securities grouped by asset type: Fair Value March 31, 2021 December 31, 2020 Amortized Cost Gross Unrealized Gains Gross Unrealized Losses Estimated Fair Value Amortized Cost Gross Unrealized Gains Gross Unrealized Losses Estimated Fair Value (in thousands) Corporate bonds Level 2 $ 100,413 $ 19 $ (37) $ 100,395 $ 96,999 $ 74 $ (9) $ 97,064 Commercial paper Level 2 124,870 — — 124,870 139,791 — — 139,791 Asset-backed securities Level 2 49,624 3 (15) 49,612 39,243 15 (1) 39,257 U.S. treasury securities Level 1 127,490 46 (1) 127,535 124,461 131 (2) 124,590 Money market funds Level 1 30,540 — — 30,540 50,524 — — 50,524 Total marketable securities $ 432,937 $ 68 $ (53) $ 432,952 $ 451,018 $ 220 $ (12) $ 451,226 We estimate the fair value of marketable securities classified as Level 1 using quoted market prices for these or identical investments obtained from a commercial pricing service. We estimate the fair value of marketable securities classified as Level 2 using inputs that may include benchmark yields, reported trades, broker/dealer quotes and issuer spreads. We periodically review our debt securities to determine if any of our investments is impaired due to credit-related or other issues. If the fair value of our investment in any debt security is less than our amortized cost basis, we determine whether an allowance for credit losses is appropriate by assessing quantitative and subjective factors including, but not limited to, the nature of security, changes in credit ratings, analyst reports concerning the security’s issuer and industry, interest rate fluctuations and general market conditions. Unrealized losses on our available-for-sale debt securities as of March 31, 2021 were not significant and were due to changes in interest rates. Accordingly, we have not recorded an allowance for credit losses associated with these investments. We do not intend to sell the investments that currently have unrealized losses. It is highly unlikely that we will sell any of our investments before recovery of their amortized cost basis, which may be at maturity. We classified accrued interest on our marketable securities of $1.7 million and $1.3 million as of March 31, 2021 and December 31, 2020, respectively, as prepaid and other current assets on our condensed consolidated balance sheets. |