Preferred stock (Details) (USD $) In Millions, except Share data, unless otherwise specified	3 Months Ended	0 Months Ended	12 Months Ended
	Mar. 28, 2014 Director	Feb. 21, 2014 Convertible Preferred Stock [Member]	Dec. 27, 2013 Convertible Preferred Stock [Member]
Class of Stock [Line Items]
Preferred stock issued (in shares)			1,000
Preferred stock conversion ratio (in hundredths)			67.90%
Percentage of acquire and cancel outstanding senior convertible notes (in hundredths)	90.00%
Convertible senior notes	$ 22.3
Preferred stock conversion to common stock (in shares)		8,200,000
Number of directors appointed	3
Number of directors of the board before expansion	7
Number of directors of the board after expansion	9