Financing: Summary of ATM Activity (Details) - Common Stock - USD ($) $ / shares in Units, shares in Millions, $ in Millions	12 Months Ended
Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
Proceeds, (net of issuance costs)	$ 181.6	$ 118.7	$ 90.3
Number of shares issued	3.3	2.0	1.3
Average price per share	$ 55.63	$ 59.04	$ 69.74
Payments of Stock Issuance Costs	$ (1.8)	$ (1.2)	$ (0.9)
August 4, 2020 ATM Program
Proceeds, (net of issuance costs)	$ 0.0	$ 48.5	$ 90.3
Number of shares issued	0.0	0.8	1.3
Payments of Stock Issuance Costs	$ 0.0	$ (0.5)	$ (0.9)
June 16, 2023 ATM Program
Proceeds, (net of issuance costs)	$ 181.6	$ 70.2	$ 0.0
Number of shares issued	3.3	1.2	0.0
Payments of Stock Issuance Costs	$ (1.8)	$ (0.7)	$ 0.0