Restructuring - Actual and Estimated Pre-Tax Expenses (Details) - Technical Nonwovens - USD ($) $ in Thousands	6 Months Ended	12 Months Ended
	Mar. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Restructuring Cost and Reserve [Line Items]
Total estimated expenses		$ 534	$ 5,000
Total pre-tax expense incurred	$ 1,196	662
Estimated remaining expense at March 31, 2018	3,804	4,338
Severance and Related Expenses
Restructuring Cost and Reserve [Line Items]
Total estimated expenses		315	1,200
Total pre-tax expense incurred	496	181
Estimated remaining expense at March 31, 2018	704	1,019
Contract Termination Expenses
Restructuring Cost and Reserve [Line Items]
Total estimated expenses		0	300
Total pre-tax expense incurred	154	154
Estimated remaining expense at March 31, 2018	146	146
Facility Exit, Move and Set-up Expenses
Restructuring Cost and Reserve [Line Items]
Total estimated expenses		219	$ 3,500
Total pre-tax expense incurred	546	327
Estimated remaining expense at March 31, 2018	$ 2,954	$ 3,173