Commitments and Contingencies (Narrative) (Details) - USD ($) $ in Millions		1 Months Ended	3 Months Ended	9 Months Ended	12 Months Ended
	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2018	Dec. 31, 2017	Dec. 31, 2016
Loss Contingencies [Line Items]
Environmental Compliance Plan, Outside Audit Period				5 years
Antidumping Duties [Member]
Loss Contingencies [Line Items]
Loss Contingency Multilayered Hardwood Products Purchase Percentage					8.00%	7.00%
Litigation Relating to Formaldehyde Abrasion MDL's [Member]
Loss Contingencies [Line Items]
Settlement Agreement Date				March 15, 2018
Litigation Settlement, Amount		$ 36.0			$ 36.0
Settlement Liability, Noncurrent				$ 2.2
Settlement payment	$ 0.5
Litigation Settlement, Expense			$ 1.0	$ 3.0
Cash and or Common Stock [Member] | Litigation Relating to Formaldehyde Abrasion MDL's [Member]
Loss Contingencies [Line Items]
Litigation Settlement, Amount		22.0
In Store Credit [Member] | Litigation Relating to Formaldehyde Abrasion MDL's [Member]
Loss Contingencies [Line Items]
Litigation Settlement, Amount		$ 14.0