Litigation and Related Matters (Narrative) (Details)		1 Months Ended	3 Months Ended			9 Months Ended		12 Months Ended	24 Months Ended
	Mar. 01, 2019 USD ($)	Sep. 30, 2010 site	Sep. 30, 2019 USD ($) Litigation	Sep. 30, 2018 USD ($)	Dec. 31, 2017 USD ($)	Sep. 30, 2019 USD ($) Litigation site	Sep. 30, 2018 USD ($)	Dec. 31, 2007	Dec. 31, 2018 USD ($)
Loss Contingencies [Line Items]
Number of active and independent litigation matters for which pursuing coverage and recoveries | Litigation			2			2
Settlement agreement amount of litigation agreement						$ 1,700,000			$ 37,500,000
Cash received from litigation settlements						6,500,000
Additional cash received from litigation settlements						200,000
Environmental liabilities			$ 2,100,000			2,100,000			12,400,000
Reserves for potential environmental liabilities			0	$ 0.5		1,000,000.0	$ 0.5
Settlement agreement amount paid for litigation agreement						19,700,000
Accounts Payable and Accrued Expenses [Member]
Loss Contingencies [Line Items]
Environmental liabilities			600,000			600,000			700,000
St. Helens [Member]
Loss Contingencies [Line Items]
Environmental liabilities			8,600,000			$ 8,600,000
Reserves for potential environmental liabilities					$ 8,600,000
Settlement agreement amount paid for litigation agreement	$ 1,000,000.0
Payments made related to environmental liabilities			$ 8,600,000
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 Goods Sold [Member]
Loss Contingencies [Line Items]
Settlement agreement amount of litigation agreement									9,200,000
SG&A Expenses [Member]
Loss Contingencies [Line Items]
Settlement agreement amount of litigation agreement						$ 1,900,000			$ 28,300,000