Income taxes (Deferred income taxes) (Details) - USD ($) $ in Thousands	Dec. 30, 2017	Dec. 31, 2016	Jan. 02, 2016
Income Tax Disclosure [Abstract]
Deferred Tax Assets Property Plant And Equipment Intangibles	$ (51,093)	$ (87,833)
Deferred Tax Assets Capital And Non Capital Loss Carryforwards	22,144	31,494
Deferred Tax Liabilities Tax Credit Carryforwards Research	1,871	1,199
Deferred Tax Assets Share Issuance Costs	0	944
Deferred Tax Assets, Inventory	5,193	5,761
Deferred Tax Assets, Accrued Interest	10,311	3,356
Deferred Tax Assets, Other	5,249	10,653
Deferred Tax Liabilities, Gross	(6,325)	(34,426)
Valuation Allowance, Amount	(9,162)	(9,090)	$ (9,347)
Deferred Income Tax Liabilities, Net, Total	$ (15,487)	$ (43,516)