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Financing: Summary of ATM Activity (Details) - Common Stock - USD ($) $ / shares in Units, $ in Millions | 12 Months Ended
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Dec. 31, 2023 | Dec. 31, 2022 | Dec. 31, 2021
Proceeds, (net of issuance costs) | $ 118.7 | $ 90.3 | $ 118.8
Number of shares issued | 2 | 1.3 | 1.8
Average price per share | $ 59.04 | $ 69.74 | $ 66.18
Payments of Stock Issuance Costs | $ (1.2) | $ (0.9) | $ (1.1)
August 4, 2020 ATM Program |  |  |
Proceeds, (net of issuance costs) | $ 48.5 | $ 90.3 | $ 118.8
Number of shares issued | 0.8 | 1.3 | 1.8
Payments of Stock Issuance Costs | $ (0.5) | $ (0.9) | $ (1.1)
June 16, 2023 ATM Program |  |  |
Proceeds, (net of issuance costs) | $ 70.2 | $ 0.0 | $ 0.0
Number of shares issued | 1.2 | 0 | 0
Payments of Stock Issuance Costs | $ (0.7) | $ 0.0 | $ 0.0

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