Revenue (Schedule of Net Sales by Major Customer Group within Each Segment) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Entity Wide Revenue Major Customer [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax	$ 326.3	$ 310.2
Mineral Fiber [Member]
Entity Wide Revenue Major Customer [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax	239.6	228.4
Mineral Fiber [Member] | Distributors [Member]
Entity Wide Revenue Major Customer [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax	169.3	159.8
Mineral Fiber [Member] | Home Centers [Member]
Entity Wide Revenue Major Customer [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax	31.0	31.1
Mineral Fiber [Member] | Direct Customers [Member]
Entity Wide Revenue Major Customer [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax	13.1	14.7
Mineral Fiber [Member] | Other [Member]
Entity Wide Revenue Major Customer [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax	26.2	22.8
Architectural Specialties [Member]
Entity Wide Revenue Major Customer [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax	86.7	81.8
Architectural Specialties [Member] | Distributors [Member]
Entity Wide Revenue Major Customer [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax	53.8	39.2
Architectural Specialties [Member] | Direct Customers [Member]
Entity Wide Revenue Major Customer [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax	30.0	42.0
Architectural Specialties [Member] | Other [Member]
Entity Wide Revenue Major Customer [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax	$ 2.9	$ 0.6