Income taxes (Tax reconciliation) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 29, 2018	Dec. 30, 2017	Dec. 31, 2016
Income Tax Disclosure [Abstract]
Earnings (loss) from continuing operations before income taxes	$ (114,521)	$ (170,397)	$ (74,361)
Canadian statutory rate	26.50%	26.50%	26.50%
Income Tax Reconciliation, Income Tax Expense (Benefit), at Federal Statutory Income Tax Rate	$ (30,348)	$ (45,155)	$ (19,706)
Income Tax Reconciliation, Foreign Income Tax Rate Differential	2,562	(9,324)	(11,329)
Unrecognized Tax Benefits, Period Increase (Decrease)	0	(452)	(1,268)
Income Tax Reconciliation, Change in Deferred Tax Assets Valuation Allowance	(3,717)	72	(267)
Income Tax Reconciliation, Goodwill Impairment	22,239	30,475	6,841
Income Tax Reconciliation Impairment Loss On Investment	0	0	0
Income Tax Reconciliation, Change in Enacted Tax Rate	1,976	(8,437)	90
Income Tax Reconciliation, Benefits of losses and credits not previously recognized	0	0	0
Income Tax Reconciliation, U.S. domestic manufacturing deduction	2,019	1,590	1,238
Income Tax Reconciliation, Other Reconciling Items	(109)	(4,598)	604
Income Tax Reconciliation Nondeductible Acquisition Costs	0	0	0
Income Tax Expense (Benefit), Continuing Operations, Total	$ (5,378)	$ (35,829)	$ (23,797)