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MARKETABLE INVESTMENT SECURITIES (Tables) | 12 Months Ended
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Dec. 31, 2023
Investments, Debt and Equity Securities [Abstract] |
Schedule of Fair Value for Available-for-Sale Securities by Major Security Type and Class of Security | The amortized cost, gross unrealized holding gains, gross unrealized holding losses, and fair value for debt securities classified as available-for-sale securities by major security type and class of security at December 31, 2023 and December 31, 2022 were as follows:
(in millions) | Amortized cost |  | Gross unrealized holding gains |  | Gross unrealized holding losses |  | Estimated fair value
December 31, 2023: |  |  |  |  |  |  |
Cash and cash equivalents: |  |  |  |  |  |  |
Cash | $ | 129.9 |  |  | $ | — |  |  | $ | — |  |  | $ | 129.9 |
Cash equivalents | 2.2 |  |  | — |  |  | — |  |  | 2.2 |
Total cash and cash equivalents | 132.1 |  |  | — |  |  | — |  |  | 132.1 |
Available-for-sale: |  |  |  |  |  |  |
Corporate bonds and notes | 8.4 |  |  | — |  |  | (0.1) |  |  | 8.3 |
Municipal bonds | 0.5 |  |  | — |  |  | — |  |  | 0.5 |
Total | $ | 141.0 |  |  | $ | — |  |  | $ | (0.1) |  |  | $ | 140.9 |
(in millions) | Amortized cost |  | Gross unrealized holding gains |  | Gross unrealized holding losses |  | Estimated fair value
December 31, 2022: |  |  |  |  |  |  |
Cash and cash equivalents: |  |  |  |  |  |  |
Cash | $ | 53.6 |  |  | $ | — |  |  | $ | — |  |  | $ | 53.6 |
Cash equivalents | 3.3 |  |  | — |  |  | — |  |  | 3.3 |
Total cash and cash equivalents | 56.9 |  |  | — |  |  | — |  |  | 56.9 |
Available-for-sale: |  |  |  |  |  |  |
Corporate bonds and notes | 66.7 |  |  | — |  |  | (1.6) |  |  | 65.1 |
Municipal bonds | 16.3 |  |  | — |  |  | (0.3) |  |  | 16.0 |
Federal agency issues | 20.7 |  |  | — |  |  | (0.7) |  |  | 20.0 |
U.S. government securities | 11.8 |  |  | — |  |  | (0.1) |  |  | 11.7 |
Total | $ | 172.4 |  |  | $ | — |  |  | $ | (2.7) |  |  | $ | 169.7 |
Schedule of Cash, Cash Equivalents, and Maturities of Debt Securities Classified as Available-For-Sale Securities | Cash, cash equivalents, and maturities of debt securities classified as available-for-sale were as follows at December 31, 2023:
(in millions) | Amortized cost |  | Estimated fair value
Cash | $ | 129.9 |  |  | $ | 129.9 |
Cash equivalents | 2.2 |  |  | 2.2 |
Available-for-sale: |  |  |
Due within one year | 8.9 |  |  | 8.8 |
Total | $ | 141.0 |  |  | $ | 140.9 |

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