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Marketable securities | 12 Months Ended
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Dec. 31, 2024
Marketable securities |
Marketable securities | Note 6 – Marketable securities: ​
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
​ | ​ | ​ | ​ | ​ | Cost or | ​ | ​ | ​
​ | ​ | ​ | ​ | ​ | amortized | ​ | Unrealized
​ | ​ | Market value | ​ | cost | ​ | loss, net
​ | ​ | (In millions)
December 31, 2023: |  | ​ |  |  | ​ |  |  | ​ |
Current assets | ​ | $ | 56.1 | ​ | $ | 56.1 | ​ | $ | —
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
Noncurrent assets | ​ | $ | 4.8 | ​ | $ | 5.0 | ​ | $ | (.2)
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
December 31, 2024: | ​ |  |  | ​ |  |  | ​ |  |
Current assets | ​ | $ | 1.9 | ​ | $ | 1.9 | ​ | $ | —
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
Noncurrent assets | ​ | $ | 5.7 | ​ | $ | 5.7 | ​ | $ | —
​
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
​ | ​ | Fair Value Measurements
​ | ​ | ​ | ​ | ​ | Quoted | ​ | Significant
​ | ​ | ​ | ​ | ​ | Prices in | ​ | Other
​ | ​ | ​ | ​ | ​ | Active | ​ | Observable
​ | ​ | ​ | ​ | ​ | Markets | ​ | Inputs
​ |  | Total |  | (Level 1) |  | (Level 2)
​ | ​ | (In millions)
December 31, 2023: |  | ​ |  |  | ​ |  |  | ​ |
Current assets - fixed income securities | ​ | $ | 56.1 | ​ | $ | — | ​ | $ | 56.1
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
Noncurrent assets: | ​ |  | ​ | ​ |  | ​ | ​ |  | ​
Fixed income securities | ​ | $ | 2.6 | ​ | $ | — | ​ | $ | 2.6
Mutual funds | ​ | ​ | 2.2 | ​ | ​ | 2.2 | ​ | ​ | —
Total | ​ | $ | 4.8 | ​ | $ | 2.2 | ​ | $ | 2.6
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
December 31, 2024: | ​ |  |  | ​ |  |  | ​ |  |
Current assets - fixed income securities | ​ | $ | 1.9 | ​ | $ | — | ​ | $ | 1.9
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
Noncurrent assets: | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
Fixed income securities | ​ | $ | 3.1 | ​ | $ | — | ​ | $ | 3.1
Mutual funds | ​ | ​ | 2.6 | ​ | ​ | 2.6 | ​ |  | —
Total | ​ | $ | 5.7 | ​ | $ | 2.6 | ​ | $ | 3.1
​ Our marketable securities consist of investments in marketable equity and debt securities. At December 31, 2023 and 2024 our current marketable securities were primarily debt securities invested in U.S. government treasuries. The fair values of our marketable debt securities are either determined using Level 1 inputs (because securities are actively traded) or determined using Level 2 inputs (because although these securities are traded, in many cases, the market is not active and the year-end valuation is generally based on the last trade of the year, which may be several days prior to December 31).

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