Segment Results (Reconciliation of Total Segment Assets to Total Consolidated Assets) (Details) - USD ($) $ in Millions	Mar. 31, 2023	Dec. 31, 2022
Segment Reporting Information [Line Items]
Total consolidated assets	$ 1,687.9	$ 1,687.2
Mineral Fiber [Member]
Segment Reporting Information [Line Items]
Total consolidated assets	1,118.9	1,096.9
Architectural Specialties [Member]
Segment Reporting Information [Line Items]
Total consolidated assets	385.3	387.5
Unallocated Corporate [Member]
Segment Reporting Information [Line Items]
Total consolidated assets	$ 183.7	$ 202.8