Restructuring - Actual and Estimated Pre-Tax Expenses (Details) - Technical Nonwovens - USD ($) $ in Thousands	3 Months Ended			9 Months Ended	12 Months Ended
	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Sep. 30, 2018	Dec. 31, 2017	Dec. 31, 2016
Restructuring Cost and Reserve [Line Items]
Total estimated expenses						$ 5,000
Total pre-tax expense incurred	$ 519	$ 885	$ 534	$ 2,600	$ 662
Estimated remaining expense	2,400			2,400	4,338
Severance and Related Expenses
Restructuring Cost and Reserve [Line Items]
Total estimated expenses						1,200
Total pre-tax expense incurred	105	185	315	786	181
Estimated remaining expense	414			414	1,019
Contract Termination Expenses
Restructuring Cost and Reserve [Line Items]
Total estimated expenses						300
Total pre-tax expense incurred	0	0	0	154	154
Estimated remaining expense	146			146	146
Facility Exit, Move and Set-up Expenses
Restructuring Cost and Reserve [Line Items]
Total estimated expenses						$ 3,500
Total pre-tax expense incurred	414	$ 700	$ 219	1,660	327
Estimated remaining expense	$ 1,840			$ 1,840	$ 3,173