Income taxes (Components of provision) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 29, 2018	Dec. 30, 2017	Dec. 31, 2016
Current Income Tax Expense (Benefit)	$ (1,595)	$ (7,930)	$ 5,931
Deferred Income Tax Expense Benefit	(3,783)	(27,899)	(29,728)
Income Tax Expense (Benefit), Continuing Operations, Total	(5,378)	(35,829)	(23,797)
US
Current Income Tax Expense (Benefit)	(3,655)	(10,346)	(1,293)
Deferred Income Tax Expense Benefit	(4,226)	(28,606)	(29,463)
CA
Current Income Tax Expense (Benefit)	(1,334)	(658)	3,560
Deferred Income Tax Expense Benefit	547	642	(12)
Europe And Other [Member]
Current Income Tax Expense (Benefit)	3,394	3,074	3,664
Deferred Income Tax Expense Benefit	$ (104)	$ 65	$ (253)