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Marketable securities | 12 Months Ended
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Dec. 31, 2023
Marketable securities |
Marketable securities | Note 6 – Marketable securities: ​
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
​ | ​ | ​ | ​ | ​ | Cost or | ​ | ​ | ​
​ | ​ | ​ | ​ | ​ | amortized | ​ | Unrealized
​ | ​ | Market value | ​ | cost | ​ | loss, net
​ | ​ | (In millions)
December 31, 2022: |  | ​ |  |  | ​ |  |  | ​ |
Current assets | ​ | $ | 75.1 | ​ | $ | 75.7 | ​ | $ | (.6)
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
Noncurrent assets | ​ | $ | 1.2 | ​ | $ | 1.2 | ​ | $ | —
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
December 31, 2023: | ​ |  |  | ​ |  |  | ​ |  |
Current assets | ​ | $ | 56.1 | ​ | $ | 56.1 | ​ | $ | —
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
Noncurrent assets | ​ | $ | 4.8 | ​ | $ | 5.0 | ​ | $ | (.2)
​ ​
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
​ | ​ | Fair Value Measurements
​ | ​ | ​ | ​ | ​ | Quoted | ​ | Significant
​ | ​ | ​ | ​ | ​ | Prices in | ​ | Other
​ | ​ | ​ | ​ | ​ | Active | ​ | Observable
​ | ​ | ​ | ​ | ​ | Markets | ​ | Inputs
​ |  | Total |  | (Level 1) |  | (Level 2)
​ | ​ | (In millions)
December 31, 2022: |  | ​ |  |  | ​ |  |  | ​ |
Current assets: | ​ |  |  | ​ |  |  | ​ |  |
Fixed income securities | ​ | $ | 73.3 | ​ | $ | — | ​ | $ | 73.3
Mutual funds | ​ |  | 1.8 | ​ |  | 1.8 | ​ |  | —
Total | ​ | $ | 75.1 | ​ | $ | 1.8 | ​ | $ | 73.3
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
Noncurrent assets - fixed income securities | ​ | $ | 1.2 | ​ | $ | — | ​ | $ | 1.2
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
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
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
​ Our marketable securities are primarily invested in U.S. government treasuries. The fair value of our marketable securities are either determined using Level 1 inputs (because the 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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