Basic and diluted loss per share (Details) - USD ($) $ / shares in Units, $ in Thousands		3 Months Ended
		Mar. 30, 2019	Mar. 31, 2018
Numerator for basic earnings (loss) per share:
Earnings (loss) attributable to SunOpta Inc.		$ 25,649	$ (4,363)
Less: dividends and accretion on Series A Preferred Stock		(1,995)	(1,967)
Earnings (loss) attributable to common shareholders		$ 23,654	$ (6,330)
Denominator for basic earnings (loss) per share:
Basic weighted-average number of shares outstanding		87,475	86,810
Basic earnings (loss) per share		$ 0.27	$ (0.07)
Numerator for diluted earnings (loss) per share:
Earnings (loss) attributable to SunOpta Inc.		$ 25,649	$ (4,363)
Less: dividends and accretion on Series A Preferred Stock	[1]		(1,967)
Earnings (loss) attributable to common shareholders		$ 25,649	$ (6,330)
Denominator for diluted earnings (loss) per share:
Basic weighted-average number of shares outstanding		87,475	86,810
Dilutive effect of the following:
Diluted weighted-average number of shares outstanding		98,999	86,810
Diluted earnings (loss) per share		$ 0.26	$ (0.07)
Series A Preferred Stock [Member]
Dilutive effect of the following:
Dilutive Securities, Effect on Basic Earnings Per Share	[1]	11,333	0
Stock Options And Restricted Stock Units [Member]
Dilutive effect of the following:
Dilutive Securities, Effect on Basic Earnings Per Share	[2]	191	0

[1] For the quarter ended March 30, 2019, it was more dilutive to assume the Preferred Stock was converted into Common Shares and, therefore, the numerator of the diluted loss per share calculation was adjusted to add back the dividends and accretion on the Preferred Stock and the denominator was adjusted to include 11,333,333 Common Shares issuable on an if-converted basis.

[2] For the quarter ended March 31, 2018, stock options and restricted stock units to purchase or receive 657,946 Common Shares, respectively, were excluded from the calculation of diluted loss per share due to their anti-dilutive effect of reducing the loss per share. In addition, for the quarters ended March 30, 2019 and March 31, 2018, options to purchase 2,566,321 and 1,984,184 Common Shares, respectively, were anti-dilutive because the exercise prices of these options were greater than the average market price.