Nature of Operations and Significant Accounting Policies (Amounts Reclassified out of Accumulated Other Comprehensive Loss) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Amortization of pension and postretirement items	$ 3.8	$ 2.5	$ 3.1
Income before income taxes	226.4	239.8	248.3
Tax impact	42.3	51.5	43.4
Net income attributable to common shareholders	184.1	188.3	204.9
Amount Reclassified from Accumulated Other Comprehensive Loss | Pension and Postretirement
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Income before income taxes	(3.7)	(2.5)	(1.2)
Tax impact	(0.6)	(0.5)	(0.3)
Net income attributable to common shareholders	(3.1)	(2.0)	(0.9)
Pension | Amount Reclassified from Accumulated Other Comprehensive Loss | Prior service costs
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Amortization of pension and postretirement items	(0.8)	(0.7)	(0.7)
Pension | Amount Reclassified from Accumulated Other Comprehensive Loss | Net gain (loss)
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Amortization of pension and postretirement items	0.3	0.0	0.6
Postretirement | Amount Reclassified from Accumulated Other Comprehensive Loss | Prior service costs
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Amortization of pension and postretirement items	(0.9)	(1.1)	(1.1)
Postretirement | Amount Reclassified from Accumulated Other Comprehensive Loss | Net gain (loss)
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Amortization of pension and postretirement items	$ (0.9)	$ (0.7)	$ 0.0