Derivative financial instruments (Details) - USD ($) $ in Thousands	3 Months Ended	6 Months Ended
Dec. 29, 2018	Dec. 30, 2017	Dec. 29, 2018	Dec. 30, 2017
Derivative financial instruments
Net derivative financial instrument gain (loss)	$ (2,417)	$ (1,361)	$ 376	$ 1,715

Amount of increase (decrease) in the fair value of derivatives recognized in the income statement.

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 4A
-Subparagraph (b)(1)
-URI http://asc.fasb.org/extlink&oid=109980867&loc=SL5618551-113959

Name:	us-gaap_DerivativeGainLossOnDerivativeNet
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration