Basic and diluted loss per share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended
	Mar. 28, 2020	Mar. 30, 2019
Numerator for basic loss per share
Earnings attributable to SunOpta Inc.	$ 3,361	$ 25,649
Less: dividends and accretion on Series A Preferred Stock	(2,025)	(1,995)
Earnings attributable to common shareholders	$ 1,336	$ 23,654
Denominator for basic loss per share
Basic weighted-average number of shares outstanding	88,161	87,475
Basic loss per share	$ 0.02	$ 0.27
Numerator for diluted loss per share
Earnings attributable to SunOpta Inc.	$ 3,361	$ 25,649
Less: dividends and accretion on Series A Preferred Stock	(2,025)	0
Loss attributable to common shareholders	$ 1,336	$ 25,649
Denominator for diluted earnings (loss) per share:
Basic weighted-average number of shares outstanding	88,161	87,475
Dilutive effect of the following:
Diluted weighted-average number of shares outstanding	89,297	98,999
Diluted loss per share	$ 0.01	$ 0.26
Stock Options And Restricted Stock Units [Member]
Dilutive effect of the following:
Dilutive Securities, Effect on Basic Earnings Per Share	1,136	191
Series A Preferred Stock [Member]
Dilutive effect of the following:
Dilutive Securities, Effect on Basic Earnings Per Share	0	11,333