Revenue (Schedule of Net Sales by Major Customer Group within Each Segment) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
Entity Wide Revenue Major Customer [Line Items]
Net sales, as reported	$ 1,445.7	$ 1,295.2	$ 1,233.1
Mineral Fiber [Member]
Entity Wide Revenue Major Customer [Line Items]
Net sales, as reported	986.0	932.4	887.4
Mineral Fiber [Member] | Distributors [Member]
Entity Wide Revenue Major Customer [Line Items]
Net sales, as reported	716.9	682.3	654.1
Mineral Fiber [Member] | Home Centers [Member]
Entity Wide Revenue Major Customer [Line Items]
Net sales, as reported	107.0	103.5	99.1
Mineral Fiber [Member] | Direct Customers [Member]
Entity Wide Revenue Major Customer [Line Items]
Net sales, as reported	60.5	57.1	61.0
Mineral Fiber [Member] | Other [Member]
Entity Wide Revenue Major Customer [Line Items]
Net sales, as reported	101.6	89.5	73.2
Architectural Specialties [Member]
Entity Wide Revenue Major Customer [Line Items]
Net sales, as reported	459.7	362.8	345.7
Architectural Specialties [Member] | Distributors [Member]
Entity Wide Revenue Major Customer [Line Items]
Net sales, as reported	224.9	192.7	174.4
Architectural Specialties [Member] | Direct Customers [Member]
Entity Wide Revenue Major Customer [Line Items]
Net sales, as reported	214.6	159.7	168.0
Architectural Specialties [Member] | Other [Member]
Entity Wide Revenue Major Customer [Line Items]
Net sales, as reported	$ 20.2	$ 10.4	$ 3.3