Discontinued Operations - Results of Discontinued Operations (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 26, 2021	Sep. 27, 2020	Sep. 26, 2021	Sep. 27, 2020
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Net (loss) / income	$ (0.7)	$ 0.2	$ (2.8)	$ (1.3)
Net loss on disposition	(0.5)	0.0	6.6	0.0
Discontinued Operations, Held-for-sale | Superform Aluminum Superplastic
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Net sales	4.9	12.7	19.5	41.0
Cost of goods sold	(4.7)	(13.3)	(20.4)	(40.4)
Gross profit / (loss)	0.2	(0.6)	(0.9)	0.6
Selling, general and administrative expenses	(1.4)	(1.4)	(3.1)	(4.1)
Restructuring charges	0.0	(0.1)	0.0	(0.1)
Other income	0.0	2.3	0.0	2.3
Operating (loss) / profit	(1.2)	0.2	(4.0)	(1.3)
Tax credit	0.5	0.0	1.2	0.0
Net (loss) / income	(0.7)	$ 0.2	(2.8)	$ (1.3)
Discontinued Operations, Held-for-sale | Superform Aluminum Superplastic | United Kingdom
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Cash consideration received	3.5		3.5
Deferred consideration payable	0.6		0.6
Net assets sold	(4.2)		$ (4.2)
Gross loss on disposition	(0.1)
Provision for income taxes	0.0
Net loss on disposition	$ (0.1)