Litigation and Related Matters (Narrative) (Details) $ in Millions	1 Months Ended	3 Months Ended	9 Months Ended		12 Months Ended	36 Months Ended
	Sep. 30, 2010 Site	Sep. 30, 2020 USD ($)	Sep. 30, 2021 USD ($) Site Litigation	Sep. 30, 2020 USD ($)	Dec. 31, 2007	Dec. 31, 2020 USD ($)
Loss Contingencies [Line Items]
Number of active and independent litigation matters for which pursuing coverage and recoveries | Litigation			2
Settlement agreement amount of litigation agreement						$ 52.5
Environmental insurance recoveries received in excess of cumulative expenses incurred			$ 4.5			5.0
Environmental liabilities			1.0			1.2
Reserves for potential environmental liabilities		$ 0.0	0.2	$ 0.0
Accounts Payable and Accrued Expenses [Member]
Loss Contingencies [Line Items]
Environmental liabilities			$ 0.5			0.3
Macon Site [Member]
Loss Contingencies [Line Items]
Number of landfills listed as Superfund site | Site			2
Number of landfills AWI entered into an Administrative Order on Consent for a Removal Action | Site	1
Submission date of final report to EPA	Oct. 11, 2016
Elizabeth City [Member]
Loss Contingencies [Line Items]
Percentage of site costs Navy agreed to pay					33.33%
Cost of Sales [Member]
Loss Contingencies [Line Items]
Settlement agreement amount of litigation agreement						9.2
SG&A Expenses [Member]
Loss Contingencies [Line Items]
Settlement agreement amount of litigation agreement						$ 38.3