Goodwill and intangible assets (Future Amortization) (Details) $ in Thousands	Dec. 30, 2017 USD ($)
Finite Lived Intangible Assets Net [Abstract]
Finite-Lived Intangible Assets, Amortization Expense, Next Twelve Months	$ 11,135
Finite-Lived Intangible Assets, Amortization Expense, Year Two	11,021
Finite-Lived Intangible Assets, Amortization Expense, Year Three	10,324
Finite-Lived Intangible Assets, Amortization Expense, Year Four	10,112
Finite-Lived Intangible Assets, Amortization Expense, Year Five	10,112
Finite-Lived Intangible Assets, Amortization Expense, after Year Five	119,355
Finite-Lived Intangible Assets, Amortization Expense, Remainder of Fiscal Year	$ 172,059