Carrying amount (including both current and noncurrent portions of the accrual) as of the balance sheet date pertaining to a specified type of cost associated with exit from or disposal of business activities or restructuring pursuant to a duly authorized plan.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 420
-SubTopic 10
-Section S99
-Paragraph 2
-Subparagraph (SAB TOPIC 5.P.4(b))
-URI http://asc.fasb.org/extlink&oid=27011515&loc=d3e140904-122747

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 420
-SubTopic 10
-Section 50
-Paragraph 1
-Subparagraph (b)(2)
-URI http://asc.fasb.org/extlink&oid=6394359&loc=d3e17939-110869

Name:	us-gaap_RestructuringReserve
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

Restructuring initiatives - Restructuring Reserve Balance Sheet Impact (Details) - USD ($) $ in Millions	Jun. 30, 2018	Dec. 30, 2017	Jul. 01, 2017	Dec. 31, 2016
Restructuring Cost and Reserve [Line Items]
Restructuring reserve	$ 4.2	$ 8.6	$ 4.3	$ 5.0
Accrued expenses and other current liabilities
Restructuring Cost and Reserve [Line Items]
Restructuring reserve	4.0		3.8
Other non-current liabilities
Restructuring Cost and Reserve [Line Items]
Restructuring reserve	$ 0.2		$ 0.5