Litigation and Related Matters (Narrative) (Details)		1 Months Ended	3 Months Ended			12 Months Ended	24 Months Ended
	Mar. 01, 2019 USD ($)	Sep. 30, 2010 site	Mar. 31, 2019 USD ($) Litigation site	Mar. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)	Dec. 31, 2007	Dec. 31, 2018 USD ($)	Feb. 01, 2018 USD ($)
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			$ 1,700,000				$ 37,500,000
Cash received from litigation settlements			6,500,000
Additional cash received from litigation settlements			200,000
Environmental liabilities			12,400,000				12,400,000
Reserves for potential environmental liabilities			1,000,000	$ 0
Settlement agreement amount paid for litigation agreement			19,700,000
Accounts Payable and Accrued Expenses [Member]
Loss Contingencies [Line Items]
Environmental liabilities			9,600,000				700,000
Accounts and Notes Receivable, Net [Member]
Loss Contingencies [Line Items]
Insurance recoveries related to environmental matters			$ 1,700,000
St. Helens [Member]
Loss Contingencies [Line Items]
Environmental liabilities								$ 8,600,000
Reserves for potential environmental liabilities					$ 8,600,000
Settlement agreement amount paid for litigation agreement	$ 1,000,000
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