Commitments and contingencies (Narrative) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 30, 2017	Dec. 31, 2016	Jan. 02, 2016
Loss Contingencies [Line Items]
Letters of Credit Outstanding, Amount	$ 9,400	$ 4,300
Operating Leases, Rent Expense, Minimum Rentals	28,000	27,900	$ 21,600
Litigation Settlement Expense	$ (1,024)	9,000	$ 0
Loss Contingency Damages Sought	On November 20, 2017, Treehouse Foods, Inc., several of its related entities, and its insurer filed a lawsuit against the Company in the Circuit Court of Cook County, Illinois titled Treehouse Foods, Inc. et al. v. SunOpta Grains and Food, Inc. The Company was served with the Summons and Complaint on January 24, 2018. The plaintiffs allege economic damages resulting from the Company’s 2016 voluntary recall of certain roasted sunflower kernel products due to the potential for Listeria monocytogenes contamination. The case includes claims for breach of express and implied warranty, negligence, strict liability, and indemnity seeking $16.2 million in damages. There are no allegations of personal injury. The Company intends to vigorously defend itself against these claims. The Company cannot reasonably predict the outcome of this claim, nor can it estimate the amount of loss, or range of loss, if any, that may result from this claim.
SunOpta Foods [Member]
Loss Contingencies [Line Items]
Grain Held For Benefit Of Others	$ 400	$ 500