Segment Results (Schedule of Net Sales) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
Segment Reporting Information [Line Items]
Total net sales	$ 347.3	$ 325.0	$ 982.9	$ 928.6
Mineral Fiber [Member]
Segment Reporting Information [Line Items]
Total net sales	249.7	233.7	712.1	671.4
Architectural Specialties [Member]
Segment Reporting Information [Line Items]
Total net sales	$ 97.6	$ 91.3	$ 270.8	$ 257.2