Income taxes (Components of provision) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 30, 2017	Dec. 31, 2016	Jan. 02, 2016
Current Income Tax Expense (Benefit)	$ (7,930)	$ 5,931	$ 318
Deferred Income Tax Expense Benefit	(27,899)	(29,728)	(3,708)
Income Tax Expense (Benefit), Continuing Operations, Total	(35,829)	(23,797)	(3,390)
US
Current Income Tax Expense (Benefit)	(10,346)	(1,293)	(1,982)
Deferred Income Tax Expense Benefit	(28,606)	(29,463)	(5,971)
CA
Current Income Tax Expense (Benefit)	(658)	3,560	0
Deferred Income Tax Expense Benefit	642	(12)	2,484
Europe And Other [Member]
Current Income Tax Expense (Benefit)	3,074	3,664	2,300
Deferred Income Tax Expense Benefit	$ 65	$ (253)	$ (221)