Nature of Operations (Schedule of Net Sales to External Customers) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
Segment Reporting Information [Line Items]
Net sales to external customers	$ 1,445.7	$ 1,295.2	$ 1,233.1
Cost of goods sold	864.1	798.2	784.0
Gross profit (loss)	581.6	497.0	449.1
Selling, general and administrative expenses	308.5	262.5	237.0
Loss related to change in fair value of contingent consideration	1.6	0.1	11.0
Loss on sales of fixed assets, net	0.6	0.0	0.0
Equity (earnings) from unconsolidated affiliates, net	(103.4)	(89.3)	(77.6)
Segment operating income (loss)	374.3	323.7	278.7
Segment assets	1,842.7	1,672.4	1,687.2
Investment in unconsolidated affiliates	27.2	17.4	23.9
Depreciation and amortization	103.2	89.2	83.7
Purchases of property, plant and equipment	82.8	83.8	74.8
Mineral Fiber [Member]
Segment Reporting Information [Line Items]
Net sales to external customers	986.0	932.4	887.4
Cost of goods sold	586.2	574.1	559.4
Gross profit (loss)	399.8	358.3	328.0
Selling, general and administrative expenses	180.8	161.9	144.7
Loss related to change in fair value of contingent consideration	0.2
Loss on sales of fixed assets, net	0.6
Equity (earnings) from unconsolidated affiliates, net	(104.3)	(89.3)	(77.6)
Segment operating income (loss)	322.5	285.7	260.9
Segment assets	1,063.8	1,091.9	1,096.9
Investment in unconsolidated affiliates	22.6	17.4	23.9
Depreciation and amortization	80.2	75.3	69.5
Purchases of property, plant and equipment	64.3	67.2	63.8
Architectural Specialties [Member]
Segment Reporting Information [Line Items]
Net sales to external customers	459.7	362.8	345.7
Cost of goods sold	276.3	222.4	222.3
Gross profit (loss)	183.4	140.4	123.4
Selling, general and administrative expenses	126.7	99.4	90.7
Loss related to change in fair value of contingent consideration	1.4	0.1	11.0
Segment operating income (loss)	55.3	40.9	21.7
Segment assets	602.2	421.1	387.5
Depreciation and amortization	23.0	13.9	14.2
Purchases of property, plant and equipment	18.5	16.6	11.0
Unallocated Corporate [Member]
Segment Reporting Information [Line Items]
Cost of goods sold	1.6	1.7	2.3
Gross profit (loss)	(1.6)	(1.7)	(2.3)
Selling, general and administrative expenses	1.0	1.2	1.6
Equity (earnings) from unconsolidated affiliates, net	0.9
Segment operating income (loss)	(3.5)	(2.9)	(3.9)
Segment assets	176.7	$ 159.4	$ 202.8
Investment in unconsolidated affiliates	$ 4.6