Segment Results (Reconciliation of Total Segment Assets to Total Consolidated Assets) (Details) - USD ($) $ in Millions	Jun. 30, 2024	Dec. 31, 2023
Segment Reporting Information [Line Items]
Total consolidated assets	$ 1,820.2	$ 1,672.4
Mineral Fiber [Member]
Segment Reporting Information [Line Items]
Total consolidated assets	1,098.1	1,091.9
Architectural Specialties [Member]
Segment Reporting Information [Line Items]
Total consolidated assets	549.6	421.1
Unallocated Corporate [Member]
Segment Reporting Information [Line Items]
Total consolidated assets	$ 172.5	$ 159.4