Litigation and Related Matters (Narrative) (Details) $ in Millions	1 Months Ended	3 Months Ended	12 Months Ended			24 Months Ended
	Sep. 30, 2010 site	Jun. 30, 2019 USD ($)	Dec. 31, 2019 USD ($) Litigation site	Dec. 31, 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
Settlement agreement amount of litigation agreement			$ 1.9			$ 37.5
Cash received from litigation settlements			6.5
Additional cash received from litigation settlements			0.4
Environmental liabilities			1.6	$ 12.4		12.4
Reserves for potential environmental liabilities			1.0	0.5
Settlement agreement amount paid for litigation agreement			19.7
Accounts Payable and Accrued Expenses [Member]
Loss Contingencies [Line Items]
Environmental liabilities			0.1	0.7		$ 0.7
St. Helens [Member]
Loss Contingencies [Line Items]
Environmental liabilities payment		$ 1.0	$ 8.6
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				9.2
SG&A Expenses [Member]
Loss Contingencies [Line Items]
Settlement agreement amount of litigation agreement			$ 2.3	$ 28.3