Revenue (Schedule of Net Sales by Major Customer Group within Each Segment) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2022	Sep. 30, 2021	Sep. 30, 2022	Sep. 30, 2021
Entity Wide Revenue Major Customer [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax	$ 325.0	$ 292.2	$ 928.6	$ 824.1
Mineral Fiber [Member]
Entity Wide Revenue Major Customer [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax	233.7	214.5	671.4	611.3
Mineral Fiber [Member] | Distributors [Member]
Entity Wide Revenue Major Customer [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax	173.8	161.5	495.0	453.5
Mineral Fiber [Member] | Home Centers [Member]
Entity Wide Revenue Major Customer [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax	24.0	20.2	75.6	68.4
Mineral Fiber [Member] | Direct Customers [Member]
Entity Wide Revenue Major Customer [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax	16.1	16.3	46.6	44.3
Mineral Fiber [Member] | Retailers And Other
Entity Wide Revenue Major Customer [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax	19.8	16.5	54.2	45.1
Architectural Specialties [Member]
Entity Wide Revenue Major Customer [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax	91.3	77.7	257.2	212.8
Architectural Specialties [Member] | Distributors [Member]
Entity Wide Revenue Major Customer [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax	44.7	41.4	129.4	116.0
Architectural Specialties [Member] | Direct Customers [Member]
Entity Wide Revenue Major Customer [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax	45.3	35.7	125.0	94.6
Architectural Specialties [Member] | Retailers And Other
Entity Wide Revenue Major Customer [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax	$ 1.3	$ 0.6	$ 2.8	$ 2.2