Restructuring and other strategic initiatives - Income Statement Location (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 28, 2020	Mar. 30, 2019
Restructuring Cost and Reserve
Restructuring expenses	$ 1.9	$ 3.3
Total expenses related to other strategic initiatives	0.6	(0.2)
Restructuring expenses: | —Severance
Restructuring Cost and Reserve
Restructuring expenses	0.2	2.6
Restructuring expenses: | —Professional fees
Restructuring Cost and Reserve
Restructuring expenses	0.2	0.6
Restructuring expenses: | —Other restructuring expenses
Restructuring Cost and Reserve
Restructuring expenses	1.5	0.1
Cost of sales
Restructuring Cost and Reserve
Severance-related expenses (included in cost of sales)	0.1	0.0
SG&A
Restructuring Cost and Reserve
Severance-related expenses (included in cost of sales)	$ 0.5	$ (0.2)