Goodwill - Schedule of changes in the carrying amount of goodwill and accumulated impairment losses by reporting segment (Details) - USD ($) $ in Millions	3 Months Ended		12 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Goodwill [Abstract]
Goodwill			$ 72.6	$ 72.7	$ 65.5
Accumulated impairment losses			(34.0)	(34.0)	(32.4)
Net			38.6	38.7	33.1
Acquisitions			0.0	0.8
Acquisitions			(0.1)	(6.4)
Impairment			0.0	(1.6)	0.0
Total activity			(0.1)	5.6
Infrastructure Solutions
Goodwill [Abstract]
Goodwill			39.4	39.4	32.7
Accumulated impairment losses			(21.8)	(21.8)	(20.2)
Net			17.6	17.6	12.5
Acquisitions			0.1	0.3
Acquisitions	$ (0.1)			(6.4)
Impairment		$ 1.6
Total activity			0.0	5.1
Materials Solutions
Goodwill [Abstract]
Goodwill			33.2	33.3	32.8
Accumulated impairment losses			(12.2)	(12.2)	(12.2)
Net			21.0	21.1	$ 20.6
Acquisitions			(0.1)	0.5
Acquisitions			0.0	0.0
Impairment				0.0
Total activity			$ (0.1)	$ 0.5