Litigation and Related Matters (Narrative) (Details) $ in Millions	1 Months Ended	3 Months Ended	12 Months Ended
	Sep. 30, 2010 site	Dec. 31, 2017 USD ($) Litigation	Dec. 31, 2017 USD ($) Litigation site	Dec. 31, 2016 USD ($)	Dec. 31, 2007
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			$ 30.5
Potential environmental liabilities		$ 13.5	13.5	$ 4.7
Reserves for potential environmental liabilities			$ 10.1	$ 2.9
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%
St. Helens [Member]
Loss Contingencies [Line Items]
Reserves for potential environmental liabilities		$ 8.6
Cost Of Goods Sold [Member]
Loss Contingencies [Line Items]
Settlement agreement amount of litigation agreement			$ 11.2
SG&A Expenses [Member]
Loss Contingencies [Line Items]
Settlement agreement amount of litigation agreement			$ 19.3