Revenue (Schedule of Net Sales by Major Customer Group within Each Segment) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Entity Wide Revenue Major Customer [Line Items]
Revenue From Contract With Customer Excluding Assessed Tax	$ 1,106.6	$ 936.9	$ 1,038.1
Mineral Fiber [Member]
Entity Wide Revenue Major Customer [Line Items]
Revenue From Contract With Customer Excluding Assessed Tax	818.5	726.0	826.6
Mineral Fiber [Member] | Distributors [Member]
Entity Wide Revenue Major Customer [Line Items]
Revenue From Contract With Customer Excluding Assessed Tax	603.9	525.2	622.9
Mineral Fiber [Member] | Home Centers [Member]
Entity Wide Revenue Major Customer [Line Items]
Revenue From Contract With Customer Excluding Assessed Tax	94.4	96.1	85.2
Mineral Fiber [Member] | Direct Customers [Member]
Entity Wide Revenue Major Customer [Line Items]
Revenue From Contract With Customer Excluding Assessed Tax	59.2	54.3	61.2
Mineral Fiber [Member] | Retailers And Other
Entity Wide Revenue Major Customer [Line Items]
Revenue From Contract With Customer Excluding Assessed Tax	61.0	50.4	57.3
Architectural Specialties [Member]
Entity Wide Revenue Major Customer [Line Items]
Revenue From Contract With Customer Excluding Assessed Tax	288.1	210.9	211.5
Architectural Specialties [Member] | Distributors [Member]
Entity Wide Revenue Major Customer [Line Items]
Revenue From Contract With Customer Excluding Assessed Tax	150.5	135.5	138.3
Architectural Specialties [Member] | Direct Customers [Member]
Entity Wide Revenue Major Customer [Line Items]
Revenue From Contract With Customer Excluding Assessed Tax	134.6	73.3	68.0
Architectural Specialties [Member] | Retailers And Other
Entity Wide Revenue Major Customer [Line Items]
Revenue From Contract With Customer Excluding Assessed Tax	$ 3.0	$ 2.1	$ 5.2