Revenue (Schedule of Net Sales by Major Customer Group within Each Segment) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2023	Jun. 30, 2022	Jun. 30, 2023	Jun. 30, 2022
Entity Wide Revenue Major Customer [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax	$ 325.4	$ 321.0	$ 635.6	$ 603.6
Mineral Fiber [Member]
Entity Wide Revenue Major Customer [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax	234.0	234.5	462.4	437.7
Mineral Fiber [Member] | Distributors [Member]
Entity Wide Revenue Major Customer [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax	174.6	177.7	334.4	321.2
Mineral Fiber [Member] | Home Centers [Member]
Entity Wide Revenue Major Customer [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax	23.4	23.5	54.5	51.6
Mineral Fiber [Member] | Direct Customers [Member]
Entity Wide Revenue Major Customer [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax	15.2	16.3	29.9	30.6
Mineral Fiber [Member] | Other [Member]
Entity Wide Revenue Major Customer [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax	20.8	17.0	43.6	34.3
Architectural Specialties [Member]
Entity Wide Revenue Major Customer [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax	91.4	86.5	173.2	165.9
Architectural Specialties [Member] | Distributors [Member]
Entity Wide Revenue Major Customer [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax	45.9	45.9	85.1	84.7
Architectural Specialties [Member] | Direct Customers [Member]
Entity Wide Revenue Major Customer [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax	44.4	40.3	86.4	79.7
Architectural Specialties [Member] | Other [Member]
Entity Wide Revenue Major Customer [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax	$ 1.1	$ 0.3	$ 1.7	$ 1.5