Leases - Schedule of supplemental balance sheet information (Details) $ in Thousands	6 Months Ended
	Jun. 27, 2020 USD ($) operating_lease	Dec. 28, 2019 USD ($)
Leases [Abstract]
Number of equipment operating leases | operating_lease	5
Assets
Operating lease assets	$ 45,175	$ 46,313
Finance lease assets	2,581	2,371
Total leased assets	47,756	48,685
Liabilities
Operating	(13,176)	(13,108)
Finance	(1,075)	(1,022)
Noncurrent
Operating	(33,562)	(34,573)
Finance	(1,553)	(1,685)
Total lease liabilities	$ (49,366)	(50,388)
Finance Lease, Right-of-Use Asset, Statement of Financial Position [Extensible List]	us-gaap:PropertyPlantAndEquipmentNet
Operating Lease, Liability, Current, Statement of Financial Position [Extensible List]	us-gaap:AccruedLiabilitiesCurrent
Finance Lease, Liability, Current, Statement of Financial Position [Extensible List]	us-gaap:LongTermDebtAndCapitalLeaseObligationsCurrent
Operating Lease, Liability, Noncurrent, Statement of Financial Position [Extensible List]	us-gaap:OtherLiabilitiesNoncurrent
Finance Lease, Liability, Noncurrent, Statement of Financial Position [Extensible List]	us-gaap:LongTermDebtAndCapitalLeaseObligations
Operating right of-use lease assets	$ 13,965	9,657
Financing right of-use lease assets	$ 2,069	$ 1,592