Business Segment Information (Details) - USD ($) $ in Millions	3 Months Ended			6 Months Ended
	Jun. 30, 2020	Mar. 31, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Business segment
Net sales	$ 161.4		$ 253.4	$ 395.0	$ 493.1
Operating income (loss)	(58.5)		19.8	(34.9)	37.2
Asset restructuring and impairment costs	55.3		2.0	55.3	2.0
Loss on debt extinguishment (Note 5)	1.9		0.0	1.9	0.0
COVID-19 costs	0.4	$ 1.1	0.0	1.5	0.0
Other restructuring and non-routine costs	1.3		1.5	2.7	1.5
Due diligence and transaction costs	0.1		0.0	1.1	0.0
Unallocated corporate costs
Business segment
Operating income (loss)	(7.1)		(5.6)	(14.5)	(11.4)
Loss on debt extinguishment (Note 5)	1.8			1.8
COVID-19 costs	0.2			0.2
Other restructuring and non-routine costs	0.3			0.6
Due diligence and transaction costs	0.1			1.1
Restructuring charges			0.1		0.1
Technical Products | Operating segments
Business segment
Net sales	106.1		146.4	248.3	286.4
Operating income (loss)	(47.3)		12.5	(31.1)	23.8
Asset restructuring and impairment costs	51.6			51.6
Loss on debt extinguishment (Note 5)	0.1			0.1
COVID-19 costs	0.1			0.7
Other restructuring and non-routine costs	0.2			0.4
Electricity grid charge			0.4		0.4
Fine Paper and Packaging | Operating segments
Business segment
Net sales	55.3		107.0	146.7	206.7
Operating income (loss)	(4.1)		12.9	10.7	24.8
Asset restructuring and impairment costs	3.7			3.7
COVID-19 costs	0.1		3.0	0.6	3.0
Other restructuring and non-routine costs	$ 0.8			$ 1.7
Accelerated depreciation			2.0		2.0
Indirect tax audit expense			0.6		0.6
Inventory reserve related to termination of royalty arrangement			$ 0.4		$ 0.4