Preferred stock (Details) (USD $) In Millions, except Share data, unless otherwise specified	3 Months Ended	12 Months Ended
	Mar. 29, 2013	Dec. 28, 2012
Class of Stock [Line Items]
Warrants issued to purchase common stock (in hundredths)		19.90%
Preferred Stock, no par value (in dollars per share)	$ 0	0
Convertible senior notes	$ 22.3
Equity receivable by lender (in hundredths)	67.90%
Maximum percentage of principal amount of debt to be exchanged for loan (in hundredths)	80.00%
Original Lender ownership percentage (in hundredths)	49.00%
Increase in Oaktree's ownership of total common stock (in hundredths)		64.38%
Preferred stock conversion ratio adjustment fair value	5.8
Warrant [Member]
Class of Stock [Line Items]
Warrant liability mark to market adjustment recorded in other income	$ 2.9
Convertible Preferred Stock [Member]
Class of Stock [Line Items]
Preferred stock issued (in shares)	1,000
Preferred Stock, no par value (in dollars per share)	$ 0
Preferred stock redemption price (in dollars per share)	$ 0.10
Preferred stock conversion ratio (in hundredths)	67.90%	64.38%