Segment Information (Details) $ in Millions	3 Months Ended
	Mar. 31, 2018 USD ($) segment	Mar. 31, 2017 USD ($)	Dec. 31, 2017 USD ($)
Segment Reporting Information [Line Items]
Assets	$ 1,547.2		$ 1,542.5
Number of operating segments | segment	2
Number of reportable segments | segment	2
Net Sales [Abstract]
Percentage of Net Sales (in hundredths)	100.00%	100.00%
Revenue, Net	$ 261.9	$ 233.3
Operating Profit [Abstract]
Operating Profit	$ 35.0	$ 27.6
Operating Profit (in hundredths)	100.00%	100.00%
Operating Segments [Member] | Engineered Papers [Member]
Segment Reporting Information [Line Items]
Assets	$ 816.1		811.7
Net Sales [Abstract]
Percentage of Net Sales (in hundredths)	56.00%	57.10%
Revenue, Net	$ 146.6	$ 133.3
Operating Profit [Abstract]
Operating Profit	$ 33.9	$ 27.9
Operating Profit (in hundredths)	96.90%	101.10%
Operating Segments [Member] | Advanced Materials & Structures Segment [Member]
Segment Reporting Information [Line Items]
Assets	$ 543.6		537.6
Net Sales [Abstract]
Percentage of Net Sales (in hundredths)	44.00%	42.90%
Revenue, Net	$ 115.3	$ 100.0
Operating Profit [Abstract]
Operating Profit	$ 10.6	$ 8.9
Operating Profit (in hundredths)	30.30%	32.20%
Unallocated [Member]
Segment Reporting Information [Line Items]
Assets	$ 187.5		$ 193.2
Operating Profit [Abstract]
Operating Profit	$ (9.5)	$ (9.2)
Operating Profit (in hundredths)	(27.20%)	(33.30%)