Supplemental Cash Flow Information (Details) - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2024	Sep. 30, 2023
Supplemental Cash Flow [Line Items]
Total interest paid	$ 27.5	$ 25.0
Income taxes paid	0.1	0.2
Income taxes recovered	(31.3)	(0.1)
Income taxes paid (recovered), net	(31.2)	0.1
Noncash activity for a lease commenced	3.3
Senior unsecured fixed rate notes
Supplemental Cash Flow [Line Items]
Total interest paid	7.0	7.0
Junior subordinated debentures
Supplemental Cash Flow [Line Items]
Total interest paid	18.6	17.2
Other indebtedness
Supplemental Cash Flow [Line Items]
Total interest paid	$ 1.9	$ 0.8