Leases - ROU assets and lease liabilities (Detail) - USD ($) $ in Thousands	Sep. 26, 2020	Dec. 28, 2019
Right-of-use assets
Operating lease assets	$ 59,991	$ 53,758
Finance lease assets	4,389	2,531
Current
Operating lease liabilities	7,735	5,168
Non-current
Operating lease liabilities	61,184	53,940
Operating Right Of Use Assets [Member]
Right-of-use assets
Operating lease assets	59,991	53,758
Property, Plant and Equipment [Member]
Right-of-use assets
Finance lease assets	4,389	2,531
Current Operating Lease Liabilities [Member]
Current
Operating lease liabilities	7,735	5,168
Accrued Expenses And Other Current Liabilities [Member]
Current
Finance lease liabilities	1,441	546
Non Current Operating Lease Liabilities [Member]
Non-current
Operating lease liabilities	61,184	53,940
Other Liabilities [Member]
Non-current
Finance lease liabilities	$ 2,997	$ 2,042