Commitments and contingencies (Narrative) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 29, 2018	Dec. 30, 2017	Dec. 31, 2016
Loss Contingencies [Line Items]
Letters of Credit Outstanding, Amount	$ 10,900	$ 9,400
Operating Leases, Rent Expense, Minimum Rentals	$ 22,700	28,000	$ 27,900
Loss Contingency Allegations	On April 19, 2013, a class-action complaint, in the case titled De Jesus, et al. v. Frozsun, Inc. d/b/a Frozsun Foods, was filed against Sunrise Growers, Inc. (“Sunrise”) (then named Frozsun, Inc.) in California Superior Court, Santa Barbara County seeking damages, equitable relief and reasonable attorneys’ fees for alleged wage and hour violations. This case included claims for failure to pay all hours worked, failure to pay overtime wages, meal and rest period violations, waiting-time penalties, improper wage statements and unfair business practices. The putative class included 10,611 non-exempt hourly employees from Sunrise’s production facilities in Santa Maria and Oxnard, California. The parties attended mediation on October 12, 2017 and reached a general agreement to resolve the matter on a class-wide basis for $5.0 million. After negotiating the remaining details of the settlement, the parties obtained preliminary approval of the class action settlement on May 14, 2018. Settlement class members had until August 20, 2018, to opt out or object to the settlement terms. A final fairness hearing with the Court was held on September 17, 2018 and the settlement was granted final approval. Full payment of the settlement amount was made to the third-party settlement administrator in October 2018. The Company recovered the full amount paid under the settlement through insurance coverage and an escrow account established in connection with the Company’s acquisition of Sunrise.
Litigation Settlement Expense	$ 0	(1,024)	$ 9,000
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. After the Company removed the case to the United States District Court for the Northern District of Illinois, the plaintiffs filed an Amended Complaint on April 23, 2018 and a second Amended Complaint on October 12, 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 contract, express and implied warranties and product guarantees, negligence, strict liability, and indemnity seeking $16.2 million in damages. There are no allegations of personal injury. The Company is vigorously defending 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	$ 200	$ 400