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Marketable securities (Tables) | 9 Months Ended
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Sep. 30, 2024
Marketable securities |
Schedule of 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)
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
September 30, 2024: | ​ |  |  | ​ |  |  | ​ |  |
Current assets | ​ | $ | 2.1 | ​ | $ | 2.1 | ​ | $ | —
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
Noncurrent assets | ​ | $ | 5.3 | ​ | $ | 5.1 | ​ | $ | .2

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- Definition Tabular disclosure of marketable securities. This may consist of investments in certain debt and equity securities, short-term investments and other assets. + References No definition available. + Details
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