Revenue (Schedule of Net Sales by Major Customer Channel within Each Segment) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2025	Mar. 31, 2024
Entity Wide Revenue Major Customer [Line Items]
Net sales	$ 382.7	$ 326.3
Mineral Fiber [Member]
Entity Wide Revenue Major Customer [Line Items]
Net sales	245.1	239.6
Mineral Fiber [Member] | Distributors [Member]
Entity Wide Revenue Major Customer [Line Items]
Net sales	180.0	169.3
Mineral Fiber [Member] | Home Centers [Member]
Entity Wide Revenue Major Customer [Line Items]
Net sales	27.0	31.0
Mineral Fiber [Member] | Direct Customers [Member]
Entity Wide Revenue Major Customer [Line Items]
Net sales	14.1	13.1
Mineral Fiber [Member] | Other [Member]
Entity Wide Revenue Major Customer [Line Items]
Net sales	24.0	26.2
Architectural Specialties [Member]
Entity Wide Revenue Major Customer [Line Items]
Net sales	137.6	86.7
Architectural Specialties [Member] | Distributors [Member]
Entity Wide Revenue Major Customer [Line Items]
Net sales	54.3	53.8
Architectural Specialties [Member] | Direct Customers [Member]
Entity Wide Revenue Major Customer [Line Items]
Net sales	77.4	30.0
Architectural Specialties [Member] | Other [Member]
Entity Wide Revenue Major Customer [Line Items]
Net sales	$ 5.9	$ 2.9