Revenue (Schedule of Net Sales by Major Customer Group within Each Segment) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2024	Jun. 30, 2023	Jun. 30, 2024	Jun. 30, 2023
Entity Wide Revenue Major Customer [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax	$ 365.1	$ 325.4	$ 691.4	$ 635.6
Mineral Fiber [Member]
Entity Wide Revenue Major Customer [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax	250.2	234.0	489.8	462.4
Mineral Fiber [Member] | Distributors [Member]
Entity Wide Revenue Major Customer [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax	184.9	174.6	354.2	334.4
Mineral Fiber [Member] | Home Centers [Member]
Entity Wide Revenue Major Customer [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax	24.5	23.4	55.5	54.5
Mineral Fiber [Member] | Direct Customers [Member]
Entity Wide Revenue Major Customer [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax	16.6	15.2	29.7	29.9
Mineral Fiber [Member] | Other [Member]
Entity Wide Revenue Major Customer [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax	24.2	20.8	50.4	43.6
Architectural Specialties [Member]
Entity Wide Revenue Major Customer [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax	114.9	91.4	201.6	173.2
Architectural Specialties [Member] | Distributors [Member]
Entity Wide Revenue Major Customer [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax	55.5	45.9	109.3	85.1
Architectural Specialties [Member] | Direct Customers [Member]
Entity Wide Revenue Major Customer [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax	53.7	44.4	83.7	86.4
Architectural Specialties [Member] | Other [Member]
Entity Wide Revenue Major Customer [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax	$ 5.7	$ 1.1	$ 8.6	$ 1.7