Subsequent events (Details) (USD $) In Millions, except Share data, unless otherwise specified	0 Months Ended	3 Months Ended			0 Months Ended	3 Months Ended
	Nov. 20, 2012	Mar. 11, 2013	Dec. 28, 2012	Dec. 30, 2011	Jan. 22, 2013 Subsequent Event [Member]	Mar. 11, 2013 Subsequent Event [Member]	Jan. 21, 2013 Subsequent Event [Member]
Subsequent Event [Line Items]
Common stock, shares authorized (in shares)			175,000,000	175,000,000			275,000,000
Series A preferred stock, shares authorized (in shares)							1,000
Series A preferred stock shares issued to Oaktree (in shares)					1,000
Percentage of common stock (in hundredths)					19.90%
Incremental term loan commitment		$ 23.0				$ 23.0
Conversion ratio related to term loan commitment (in hundredths)	64.38%	67.95%				67.90%