Income taxes (Deferred income taxes) (Details) - USD ($) $ in Thousands	Dec. 29, 2018	Dec. 30, 2017	Dec. 31, 2016
Income Tax Disclosure [Abstract]
Deferred Tax Assets Property Plant And Equipment Intangibles	$ (54,841)	$ (51,093)
Deferred Tax Assets Capital And Non Capital Loss Carryforwards	25,169	22,144
Deferred Tax Liabilities Tax Credit Carryforwards Research	2,004	1,871
Deferred Tax Assets, Inventory	3,755	5,193
Deferred Tax Assets, Accrued Interest	20,025	10,311
Deferred Tax Assets, Other	1,366	5,249
Deferred Tax Liabilities, Gross	(2,522)	(6,325)
Valuation Allowance, Amount	(5,445)	(9,162)	$ (9,090)
Deferred Income Tax Liabilities, Net, Total	$ (7,967)	$ (15,487)