Fair value measurements (Details) - Money Market Funds - USD ($) $ in Thousands	Mar. 28, 2020	Sep. 28, 2019
Assets:
Money market funds (cash equivalents)	$ 161,159	$ 267,806
Level 1
Assets:
Money market funds (cash equivalents)	161,159	267,806
Level 2
Assets:
Money market funds (cash equivalents)	0	0
Level 3
Assets:
Money market funds (cash equivalents)	$ 0	$ 0

Fair value portion of currency on hand as well as demand deposits with banks or financial institutions. Includes other kinds of accounts that have the general characteristics of demand deposits. Also includes short-term, highly liquid investments that are both readily convertible to known amounts of cash and so near their maturity that they present insignificant risk of changes in value because of changes in interest rates.

No definition available.

Name:	us-gaap_CashAndCashEquivalentsFairValueDisclosure
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant