Income taxes (Tax reconciliation) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 30, 2017	Dec. 31, 2016	Jan. 02, 2016
Income Tax Disclosure [Abstract]
Earnings (loss) from continuing operations before income taxes	$ (170,397)	$ (74,361)	$ (6,522)
Canadian statutory rate	26.50%	26.50%	26.50%
Income Tax Reconciliation, Income Tax Expense (Benefit), at Federal Statutory Income Tax Rate	$ (45,155)	$ (19,706)	$ (1,728)
Income Tax Reconciliation, Foreign Income Tax Rate Differential	(9,324)	(11,329)	(3,097)
Unrecognized Tax Benefits, Period Increase (Decrease)	(452)	(1,268)	(855)
Income Tax Reconciliation, Change in Deferred Tax Assets Valuation Allowance	72	(267)	4,015
Income Tax Reconciliation, Goodwill Impairment	30,475	6,841	0
Income Tax Reconciliation Impairment Loss On Investment	0	0	(4,029)
Income Tax Reconciliation, Change in Enacted Tax Rate	(8,437)	90	(208)
Income Tax Reconciliation, Benefits of losses and credits not previously recognized	0	0	0
Income Tax Reconciliation, U.S. domestic manufacturing deduction	1,590	1,238	1,470
Income Tax Reconciliation, Other Reconciling Items	(4,598)	604	132
Income Tax Reconciliation Nondeductible Acquisition Costs	0	0	910
Income Tax Expense (Benefit), Continuing Operations, Total	$ (35,829)	$ (23,797)	$ (3,390)