Revenue (Schedule of Net Sales by Major Customer Channel within Each Segment) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2025	Sep. 30, 2024	Sep. 30, 2025	Sep. 30, 2024
Entity Wide Revenue Major Customer [Line Items]
Net sales	$ 425.2	$ 386.6	$ 1,232.5	$ 1,078.0
Mineral Fiber [Member]
Entity Wide Revenue Major Customer [Line Items]
Net sales	274.0	258.0	786.1	747.8
Mineral Fiber [Member] | Distributors [Member]
Entity Wide Revenue Major Customer [Line Items]
Net sales	205.0	188.7	585.2	542.9
Mineral Fiber [Member] | Home Centers [Member]
Entity Wide Revenue Major Customer [Line Items]
Net sales	26.6	26.7	78.6	82.2
Mineral Fiber [Member] | Direct Customers [Member]
Entity Wide Revenue Major Customer [Line Items]
Net sales	15.6	15.7	47.6	45.4
Mineral Fiber [Member] | Other [Member]
Entity Wide Revenue Major Customer [Line Items]
Net sales	26.8	26.9	74.7	77.3
Architectural Specialties [Member]
Entity Wide Revenue Major Customer [Line Items]
Net sales	151.2	128.6	446.4	330.2
Architectural Specialties [Member] | Distributors [Member]
Entity Wide Revenue Major Customer [Line Items]
Net sales	67.3	59.5	191.6	168.8
Architectural Specialties [Member] | Direct Customers [Member]
Entity Wide Revenue Major Customer [Line Items]
Net sales	76.7	63.1	235.0	146.8
Architectural Specialties [Member] | Other [Member]
Entity Wide Revenue Major Customer [Line Items]
Net sales	$ 7.2	$ 6.0	$ 19.8	$ 14.6