Goodwill and Intangible Assets (Narrative) (Details) - USD ($) $ in Millions	Sep. 30, 2026	Dec. 31, 2025
Intangible Asset, Indefinite-Lived [Line Items]
Goodwill	$ 256.6	$ 217.8
Architectural Specialties [Member]
Intangible Asset, Indefinite-Lived [Line Items]
Goodwill	256.4	217.6
Mineral Fiber [Member]
Intangible Asset, Indefinite-Lived [Line Items]
Goodwill	$ 0.2	$ 0.2

Amount, after accumulated impairment loss, of asset representing future economic benefit arising from other asset acquired in business combination or from joint venture formation or both, that is not individually identified and separately recognized.

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+ Details

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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+ Details