Segment Results (Schedule of Net Sales) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2022	Sep. 30, 2021	Sep. 30, 2022	Sep. 30, 2021
Segment Reporting Information [Line Items]
Total net sales	$ 325.0	$ 292.2	$ 928.6	$ 824.1
Mineral Fiber [Member]
Segment Reporting Information [Line Items]
Total net sales	233.7	214.5	671.4	611.3
Architectural Specialties [Member]
Segment Reporting Information [Line Items]
Total net sales	$ 91.3	$ 77.7	$ 257.2	$ 212.8