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Dividends on common stock: (Details) - USD ($) $ / shares in Units, $ in Millions | 1 Months Ended | 3 Months Ended
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May 07, 2025 | Mar. 31, 2025 | Mar. 31, 2024
Dividends on common stock |  |  |
Dividends declared per common share |  | $ 1.005 | $ 0.965
Quarterly dividends- Q2 - 2025 | Subsequent Events |  |  |
Dividends on common stock |  |  |
Dividends, date of approval | May 07, 2025 |  |
Dividends declared per common share | $ 1.01 |  |
Dividends payable | $ 48.2 |  |
Dividends payable date | Jun. 06, 2025 |  |

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