Revenue (Schedule of Net Sales by Major Customer Channel within Each Segment) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2025	Dec. 31, 2024	Dec. 31, 2023
Entity Wide Revenue Major Customer [Line Items]
Net sales	$ 1,620.8	$ 1,445.7	$ 1,295.2
Mineral Fiber [Member]
Entity Wide Revenue Major Customer [Line Items]
Net sales	1,030.7	986.0	932.4
Mineral Fiber [Member] | Distributors [Member]
Entity Wide Revenue Major Customer [Line Items]
Net sales	768.2	716.9	682.3
Mineral Fiber [Member] | Home Centers [Member]
Entity Wide Revenue Major Customer [Line Items]
Net sales	105.8	107.0	103.5
Mineral Fiber [Member] | Direct Customers [Member]
Entity Wide Revenue Major Customer [Line Items]
Net sales	60.3	60.5	57.1
Mineral Fiber [Member] | Other [Member]
Entity Wide Revenue Major Customer [Line Items]
Net sales	96.4	101.6	89.5
Architectural Specialties [Member]
Entity Wide Revenue Major Customer [Line Items]
Net sales	590.1	459.7	362.8
Architectural Specialties [Member] | Distributors [Member]
Entity Wide Revenue Major Customer [Line Items]
Net sales	254.2	224.9	192.7
Architectural Specialties [Member] | Direct Customers [Member]
Entity Wide Revenue Major Customer [Line Items]
Net sales	309.9	214.6	159.7
Architectural Specialties [Member] | Other [Member]
Entity Wide Revenue Major Customer [Line Items]
Net sales	$ 26.0	$ 20.2	$ 10.4