Leases - Lease expense (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 28, 2020	Mar. 30, 2019
Leases [Abstract]
Operating lease cost	$ 12.5	$ 11.6
Short-term lease cost	2.3	0.9
Amortization of right-of-use assets	1.7	0.7
Interest on lease liabilities	1.0	0.2
Total finance lease cost	2.7	0.9
Sublease income	0.2	0.3
Cash paid for amounts included in the measurement of lease liabilities:
Operating cash flows from operating leases	12.6	12.9
Operating cash flows from finance leases	0.9	0.1
Financing cash flows from finance leases	1.4	0.7
Right-of-use assets obtained in exchange for lease obligations:
Operating leases	7.3	1.3
Finance leases	$ 21.7	$ 9.2