Shareholders' Equity (Reclassification out of Accumulated Other Comprehensive Income) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income [Line Items]
Cost of goods sold	$ (643.0)	$ (641.8)	$ (578.2)
Net sales	1,038.1	975.3	893.6
Interest expense	(38.4)	(39.2)	(35.4)
Tax impact	(57.1)	(53.1)	(1.5)
Total loss, net of tax	(214.5)	(185.9)	(119.6)
Other non-operating (income), net	(0.3)	4.8	(0.6)
Total expense from continuing operations, net of tax	(242.3)	(189.6)	(220.6)
Total expense from discontinued operations, net of tax expense of $- and $-	1.8	(9.6)	(4.2)
Adjustments related to Sale to Knauf	26.0	13.3	$ 105.2
Reclassification From Accumulated Other Comprehensive Loss [Member]
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income [Line Items]
Total reclassifications for the period	93.1	12.9
Reclassification From Accumulated Other Comprehensive Loss [Member] | Derivative Gain (Loss) [Member]
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income [Line Items]
Total loss, before tax	1.4	1.5
Tax impact	(0.3)	(0.4)
Total loss, net of tax	1.1	1.1
Reclassification From Accumulated Other Comprehensive Loss [Member] | Derivative Gain (Loss) [Member] | Natural Gas Commodity Contracts [Member]
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income [Line Items]
Cost of goods sold		(0.1)
Reclassification From Accumulated Other Comprehensive Loss [Member] | Derivative Gain (Loss) [Member] | Interest Rate Swap Contracts [Member]
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income [Line Items]
Interest expense	1.4	1.6
Reclassification From Accumulated Other Comprehensive Loss [Member] | Prior Service Cost Amortization [Member]
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income [Line Items]
Other non-operating (income), net	(0.2)	(0.1)
Reclassification From Accumulated Other Comprehensive Loss [Member] | Amortization of Net Actuarial Loss [Member]
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income [Line Items]
Other non-operating (income), net	10.7	14.4
Reclassification From Accumulated Other Comprehensive Loss [Member] | Pension And Postretirement Adjustments [Member]
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income [Line Items]
Total expense, before tax	10.5	14.3
Income tax expense	(2.2)	(3.0)
Total expense from continuing operations, net of tax	8.3	11.3
Total expense from discontinued operations, net of tax expense of $- and $-		0.5
Adjustments related to Sale to Knauf	3.5
Total expense, net of tax	11.8	$ 11.8
Reclassification From Accumulated Other Comprehensive Loss [Member] | Foreign Currency Translation Adjustments [Member]
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income [Line Items]
Adjustments related to Sale to Knauf	$ 80.2