Document and Entity Information - shares
9 Months Ended
Sep. 29, 2018
Nov. 02, 2018
Document And Entity Information [Abstract]    
Document Type 10-Q  
Document Period End Date Sep. 29, 2018  
Amendment Flag false  
Document Fiscal Year Focus 2018  
Document Fiscal Period Focus Q3  
Entity Registrant Name SunOpta Inc.  
Entity Central Index Key 0000351834  
Entity Current Reporting Status Yes  
Entity Voluntary Filers No  
Current Fiscal Year End Date --12-29  
Entity Filer Category Large Accelerated Filer  
Entity Well Known Seasoned Issuer Yes  
Trading Symbol STKL  
Entity Common Stock Shares Outstanding   87,375,667