Income taxes - Narratives (Details) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 26, 2020	Sep. 28, 2019	Sep. 26, 2020	Sep. 28, 2019
Operating Loss Carryforwards
Income tax (benefit) expense	$ (16,000,000.0)	$ 4,400,000	$ (31,500,000)	$ (497,800,000)
Income from continuing operations before income taxes	$ 29,700,000	$ 41,900,000	$ 26,300,000	$ 171,500,000
Reported effective income tax rate (percent)	(53.90%)	10.50%	(119.80%)	(290.30%)
Change in valuation allowance	$ (8,900,000)		$ (8,900,000)
Discrete tax expense (benefit)	5,300,000		65,600,000
Non-operating cost			19,600,000	$ 0
Effect of change in tax laws			6,300,000
Luxembourg
Operating Loss Carryforwards
Change in valuation allowance			(605,100,000)
Discrete tax expense (benefit)			25,100,000
Deferred tax asset, net	26,000,000.0		26,000,000.0
Luxembourg | Discretely Recognized
Operating Loss Carryforwards
Deferred tax asset, net	13,200,000		13,200,000
Luxembourg | Recognized Through Effective Tax Rate
Operating Loss Carryforwards
Deferred tax asset, net	12,800,000		12,800,000
India
Operating Loss Carryforwards
Discrete tax expense (benefit)			(3,200,000)
U.S.
Operating Loss Carryforwards
Discrete tax expense (benefit)			(5,800,000)
Effect of change in tax laws	$ (5,800,000)
Germany and Canada
Operating Loss Carryforwards
Discrete tax expense (benefit)			$ (24,700,000)